UNIVERSITYgrCALIFORNIA 
COLLEGE  of  MINING 

DEPARTMENTAL 
LIBRARY 


BEQUEST  OF 
SAMUELBENEDICrCHRlSTY 


PROFESSOR  OF 

MINING  AND  METALLURGY 
1885-1914 


PRACTICAL    ASSAYING. 


LONDON  :     PRINTED     BY 

SPOTTISWOODE    AND    CO.,    NEW-STREET    SQUARE 
AND    PAPXIAMENT    STREET 


A   MANUAL 


OF 


PRACTICAL    ASSAYING. 


BY 


JOHN  MITCHELL,  F.C.S. 


EDITED    BY 


WILLIAM    CEOOKES,    F.E.S. 


FIFTH    EDITION. 


S.  B.  CMRISTY, 


NEW  YOKK: 
JOHN  WILEY  &  SONS,  15  ASTOE  PLACE. 

1881. 


PREFACE 

TO 

THE    FIFTH    EDITION. 


THE  experience  of  the  last  eight  years  has  shown  that 
Mr.  Mitchell's  '  Manual  of  Practical  Assaying '  still  meets 
the  demands  of  practical  men  better  than  any  other 
work  in  the  language. 

A  number  of  improvements  and  additions  have,  how- 
ever, been  rendered  necessary  in  consequence  of  the  rapid 
progress  of  chemical  science.  Some  of  the  methods  laid 
down  in  the  earlier  editions  have  been  superseded  by  more 
accurate,  rapid,  and  convenient  processes,  and  have  con- 
sequently been  omitted. 

The  Editor's  object  has  been,  not  to  enumerate  every 
known  method,  but  simply  to  present  the  reader  with 
such  as  are  found  most  useful  under  different  circum- 
stances. 

The  hopes  entertained  at  one  time  that  spectroscopic 
processes  would  become  available  in  the  assay  of  the  pre- 
cious metals  and  their  alloys  have  so  far  been  doomed  to 


303740 


VI  PREFACE   TO   THE    FIFTH    EDITION. 

disappointment,  for  reasons  which  will  be  found   in  the 
body  of  the  work. 

The  gradual  introduction  of  the  new  chemical  nomen- 
clature and  notation  into  all  works  of  reference  has  induced 
the  Editor  to  take  the  same  step  in  the  present  volume. 
The  change  has  been  made,  however,  in  a  manner  which, 
it  is  hoped,  will  not  occasion  perplexity.  The  atomic 
weights  of  the  elementary  bodies  have  been  corrected 
according  to  the  most  recent  determinations. 

LONDON:  July  1881. 


EXTRACTS    FROM    THE 

PEEFACE  TO  THE  TRIED  EDITION. 


IN  THIS  EDITION  are  incorporated  all  the  late  impoitant 
discoveries  in  Assaying  made  in  this  country  and  abroad, 
and  special  care  is  devoted  to  the  very  important  Volumetric 
and  Colorimetric  Assays,  as  well  as  to  the  Blowpipe  assays. 
Most  of  the  chapters  are  entirely  rewritten,  whilst  the 
chapter  on  Crystallography — being  a  subject  only  remotely 
bearing  on  Assaying — is  left  out  altogether.  On  the 
other  hand,  in  some  cases,  it  may  seem  that  by  treating 
of  purely  analytical  details  the  limits  of  Assaying  have 
been  exceeded.  But  these  departments  are  so  closely 
related  as  to  make  it  impossible  to  fix  the  line  of  demar- 
cation between  them.  Moreover,  chemistry  is  cultivated 
by  almost  all  to  whom  this  work  is  of  interest  or  service 
so  that  it  is  hoped  these  amplifications  will  add  to  its  value 
The  old  equivalents  are  retained,  as  they  are  more  generally 
understood  by  students  of  science  who  do  not  make 
chemistry  their  chief  study. 

The  Editor  is  under  many  obligations  to  his  friend  Dr. 
Eohrig,  M.E.,  for  assistance  in  revising  the  manuscript  and 
incorporating  into  the  work  the  latest  continental  improve- 
ments, as  set  forth  in  Professor  Kerl's  Probirkumt.  The 
author  of  the  best  work  on  volumetric  analysis  which  has 


viii       EXTRACTS   FROM    PREFACE   TO   THE   THIRD    EDITION. 

yet  appeared  in  English,  Mr.  Sutton,  F.C.S.,  has  kindly 
placed  several  cuts,  &c.,  at  the  Editor's  disposal,  and  some 
descriptions  of  German  processes  hav£  been  taken  from  the 
last  English  Edition  of  Fresenius's  Quantitative  Analysi  — a 
work  which  should  be  a  standard  of  reference  for  all 
students  who  desire  to  carry  their  chemical  researches 
further  than  is  possible  to  be  treated  of  in  a  work  pro- 
fessing to  deal  only  with  Assaying. 

LONDON  :  September  1868. 


PREFACE 

TO 

THE    FIKST    EDITION. 


WHEN  the  rank  our  country  holds  among  nations,  as  regards 
her  Mining  interest,  is  taken  into  consideration,  it  must  be 
with  all  a  matter  of  surprise  that  no  work  especially  devoted 
to  the  elucidation  of  the  processes  to  be  employed  in  ascer- 
taining the  richness  in  metal  of  any  sample  of  ore  (that  is, 
in  other  terms,  its  Assay)  has  of  late  years  appeared  before 
the  British  public.  Indeed,  the  only  work  at  present  known 
in  England  is  Berthier's  '  Traite  des  Essais  par  la  Yoie 
Seche,'  which,  for  the  mere  purpose  .  of  inculcating  the 
principles  of  Assaying,  has  many  disadvantages — not  the 
least  of  which  is  its  being  written  in  a  foreign  tongue ; 
and  although  a  knowledge  of  French  is  now  so  very  general, 
yet  many  are  prevented  buying  scientific  works  in  that 
language  on  account  of  the  difficulties  of  finding  equivalents 
for  the  technicalities  which  must  necessarily  be  employed. 
It  is  also  a  very  large  work,  and  one  containing  much 
matter  which  the  assayer  does  not  need — matter  relat- 
ing to  the  composition  of  wood  and  coal  ashes,  furnace 
products,  &c.,  which  are  more  especially  adapted  for  the 
metallurgist. 


X  PREFACE   TO 

These  considerations,  coupled  with  the  paucity  of  any 
knowledge  of  Assaying,  excepting  that  confined  to  a  very 
limited  number  of  persons,  induced  the  author  of  the  follow- 
ing pages  to  turn  a  considerable  amount  of  his  attention  to 
this  subject,  more  especially  as  much  difficulty  was  ex- 
perienced in  not  having  a  suitable  text-book  for  the  use  of 
his  pupils.  A  portion  of  the  following  pages  was  drawn  up 
as  a  Manual  for  such  a  purpose ;  but,  on  consideration,  it 
was  thought  the  extension  of  such  a  work  was  so  much 
needed  that  it  was  determined  to  alter  the  original  plan  as 
far  as  was  consistent  with  the  complete  carrying  out  of  the 
object  in  view,  viz.  the  production  of  a  Manual  embodying 
information  in  every  branch  of  assaying,  either  by  the  wet 
or  the  dry  processes. 

The  following  is  a  sketch  of  the  manner  in  which  this 
is  accomplished ;  the  author  having  followed  the  excellent 
arrangement  of  Berthier  as  closely  as  possible,  from  whose 
work  also  much  matter  that  suited  these  pages,  and  which 
it  would  have  been  useless  to  rewrite,  has  been  inserted. 
Firstly,  the  Mechanical  and  Chemical  Operations  of  Assaying 
are  treated  in  full,  inclusive  of  a  description  of  the  appa- 
ratus required,  their  mode  of  use,  &c.  Secondly,  Furnaces, 
Fuel,  and  Crucibles,  together  with  a  description  of  the  best 
Pyrometers,  and  their  applications.  Thirdly,  the  Fluxes, 
their  properties,  preparation,  use,  &c.  Fourthly,  an  Essay 
on  the  use  of  the  Blowpipe,  and  all  its  appurtenances  ;  as 
Fluxes,  Supports,  &c.  Fifthly,  the  action  of  the  Fluxes  on 
some  Mineral  Substances.  Sixthly,  a  method  of  discrimi- 
nating many  Minerals  by  means  of  the  Blowpipe,  aided  by 
a  few  tests  by  the  humid  method.  Seventhly,  the  Humid 
Analysis  of  many  Mineral  Substances,  their  composition, 
locality,  &c.  (All  the  minerals  mentioned  in  the  three  last 
heads  comprehend  such  only  as  generally  come  under  the 


THE    FIRST   EDITION.  XI 

notice  of  the  Assayer.)  Eighthly,  the  complete  Assay  of 
all  the  common  Metals,  %in  addition  to  which  the  Assay  of 
Sulphur,  Chromium,  Arsenic,  Heating  power  of  Fuel,  &c., 
is  fully  discussed  ;  and  ninthly,  and  lastly,  a  copious  Table 
drawn  up  for  the  purpose  of  ascertaining  in  Assays  of  Gold 
and  Silver  the  precise  amount,  in  ounces,  pennyweights,  and 
grains,  of  Noble  metal  contained  in  a  Ton  of  Ore  from  the 
assay  of  a  given  quantity.  This  Table  is  the  most  complete 
and  copious  yet  published. 

Not  only  has  it  been  endeavoured  to  collect  all  that  is 
generally  known  on  the  subject  of  Assaying,  but  many  new 
facts  have  been  added,  and  such  matter  entered  into,  that 
the  success  of  an  assay  is  rendered  much  more  certain  ;  and 
most  assays  are  conducted  more  rapidly  and  with  greater 
exactitude  than  heretofore. 

It  has  also  been  endeavoured  to  introduce  a  new  system, 
in  which  is  pointed  out  the  rationale  of  each  process,  with 
the  chemical  action  taking  place  between  the  fluxes  and  the 
ores  in  course  of  assay,  so  that  by  paying  a  careful  attention 
to  the  matters  discussed,  so  much  of  the  chemical  nature  of 
all  ores  that  can  come  under  the  assayer's  hand  may  be 
known,  that  the  practice  by  '  rule  of  thumb  '  (a  rule  on 
which  very  little  dependence  is  to  be  placed,  excepting 
after  years  of  the  most  laborious  practice,  and  a  rule  which 
cannot  be  imparted,  excepting  the  pupil  pursue  the  same  un- 
profitable course)  must,  it  is  htoped,  be  speedily  abandoned 
when,  by  knowing  the  chemical  properties  of  the  body 
operated  on,  the  necessary  fluxes  and  processes  might  be 
at  once  indicated,  and  with  a  certainty  of  perfect  success. 

Having  premised  thus  much,  the  author  must  beg  to 
express  his  thanks  to  his  friend  Mr.  F.  Field  for  the  kind 


Xli  PREFACE    TO    THE    FIRST    EDITION. 

assistance  lie  afforded  him  whilst  experimenting  on  the 
various  modes  of  assay  described  in  the  body  of  the  work  ; 
and  trusting  that  any  little  imperfections  which  may  be 
detected  will  not  be  harshly  criticised,  but  that  it  may  be 
taken  into  consideration  that  the  author  has  attempted  to 
improve  a  branch  of  mining  knowledge  to  which  unfor- 
tunately too  little  attention  has  been  devoted,  and  to  which, 
if  he  has  added  anything  useful,  he  is  indebted  for  the  first 
principles  of  such  knowledge  to  Berthier's  '  Traite  des 
Essais,'  for  which,  to  the  talented  writer  of  the  above 
work,  he  is  under  the  most  lasting  obligation. 


CONTENTS. 


CHAPTER   I. 

PAGE 

Chemical  nomenclature       ......          1 

Non-metallic  elements  or  metalloids,  2.  Metallic  elements,  3. 

Oxides        ....  ...         4 

Salts           ....  ...         4 

Binary  compounds  containing  no  oxygen    .  .              .             .         5 

Laws  of  combination           .  '          .  "          .  .              .              .5 

Chemical  symbols  .             *             .             .  .              .             .7 

CHAPTER   IT. 

Preparation  of  the  sample  .  .  .  .  .  •-.    ;     9 

Anvil    and    stand,    11.      Hammers,    12.      Cold   chisel,    13. 

Shears,  13. 
Pestle  and  mortar  .  *•  .  .  .  .  .13 

Iron  mortar,  13.     Steel  mortar,  16.     Agate  mortars,  16. 
The  sieve    .  ......  .  .  .16 

Elutriation  *  .  .  .  .  *'        .    .'      19 

Washing,  dressing,  or  vanning       .  .  .  .   '         .       19 

The  balance  .  23 

Operation  of  weighing,  22.    Three  kinds  of  balances,  23.    Con- 
ditions of  accuracy  and  delicacy,  26. 
Weights     .  .  .  .  .  30 

Assay  weights  for  silver,  32.     Assay  weights  for  gold,  32. 
Method  of  weighing  .  .  •  ,       33 

Mene's  method,  36.     Mayer's  application,   36.     Muck's   re- 
marks, 38. 
Dry  filters  .  .38 

CHAPTER  III. 

General  preparatory  chemical  operations    .  .       49 

Calcination              .             .             •             •             «  -             .40 

Use  of  crucibles,  40. 

Roasting     ...                           •  .42 

Roasting  in  tests,  42.     Roasting  in  crucible?,  43.  Roasting 
in  platinum  capsules.  44. 


CONTENTS. 

PAGE 

Reduction  ......             .             •  44 

Reduction  by  carbonaceous  masses,  45.    Reduction  by  cemen- 
tation, 45.     Reduction  by  hydrogen  gas,  46. 

Fusion        .            V           .             *             .            V            .           '  .  46 

Solution     .             .         "'.-.'           .            ".             v                         v  47 

Glass  and  platinum  forceps           ",          '  •;            y             »              •  48 

Distillation  .           .             .             .             .             .             ,             .  49 

Liquid  distillation,  49.     Dry  distillation,  49. 

Sublimation             .             .             .             .             ,             .          '>>;  52 

Scorification,  Cupellation    .             .             f    ,          •             •          '.>  52 


CHAPTER   IV. 

Production  and  application  of  heat  .  ."         ;'•.:>   ^          ,       53 

Furnaces    .  .  ....  .  .       53 

Ash-pit,  53.     Bars,  53. 
Calcining  furnace  .  .  .  .  .  ^  „       53 

Body  of  furnace,  54. 

Chimney     .  .  •  •  .  .  54 

Evaporating  furnaces          .  .  .  .  .  .55 

The  hood,  55. 
Fusion  furnace,  wind  furnace          .  .  .  .  .55 

Body  of  furnace,  55.     Ash-pit,  56.     Bars,  57.     Chimney,  57. 
Blast  furnaces         .  ....       58 

Royal  Institution  furnace,  58.     Sefstroin's  furnace,  59.     St. 

Claire  Deville's  furnace,  60. 
Muffle  or  cupel  furnace       .          -    .  .  .  .  .60 

Aufrye's    and    d'Arcet's    furnace,     61.      Brick    furnace   for 

numbers  of  cupellations,  62.     '  Universal  furnace,'  63. 
Furnace  operations  .  .  .   .  .  .       64 

Auxiliary  apparatus  .  .  ,    -         -.  .          -    .       65 

Pokers  or  stirring  rods,  65.     Tongs,  65.     Spectacles  or  look- 
ing-glass, 66.     Curved  rod,  66.     Wrought-iron  ladle,  67. 
Ingot  moulds,  67. 
Fuel  for  furnaces    .  .  .  »  f  .  ,       68 

Coke,  68.     Charcoal,  68. 

The  effects  produced  by  wind  and  blast  furnaces    .  .    '         .       70 

Oil  and  gas  blast  furnaces  .  .  . '.          .  .         .  v . :      72 

Oil  furnaces  .  .  .  .  .  .  .       72 

Description  of  the  apparatus,  72.  Oil-lamp  furnace,  72.  Oil 
reservoir,  73.  Crucible  furnace,  73.  Management  of  the 
oil-lamp  furnace,  74.  Power  of  the  oil-lamp  furnace,  77. 
Requisite  blowing  power,  77. 

Griffin's  gas  furnace  .  .         .    »          ; -•,  .          ^  -v      78 

Operations  in  crucibles,  78.  Operations  in  muffles,  78. 
Burner,  78.  Skittle  pots,  81.  Flue,  81.  Distillation  of 
pure  zinc,  82. 


CONTEXTS.  XV 

PAGE 

Fletcher's  universal  gas  furnace      .  .  .  .  .82 

Burner,     82.      Single-jacketed    arrangement,   82.      Double- 
jacketed   chemical   furnace,    82.      Fletcher's   new  melting 
arrangement,  86.    Injector  gas  furnace,  87.    Simple  furnace, 
88.    Benzoline,  89. 
Gore's  gas  furnace  .  .  .  .  .  .  .89 

Griffin's  reverberatory  gas  furnace .  .  .  .95 

Bunsen's  gas  burner,  100.     Mounts  for  crucibles,  103.     Sup- 
porting a  crucible,  104.     Gas  furnace  for  boiling  or  evapo- 
rating, 104.     Fletcher's  solid  flame  burner,  106. 
Lutes  and  cements  .  .  .  .  .  .107 

Fire    lute,    107.      Fat   Lute,    108.      Roman    cement,    108. 
Plaster   of  Paris,    108.     Linseed   and  almond  meal,  108. 
Lime  and  egg  lute,  108.     White  lead  mixed  with  oil,  108. 
Yellow  wax,  108.     Soft  cement,  109.    Waterproof  cement, 
109.     Resinous  or  hard  cement,   110.     Caoutchouc,  110. 
Faraday's  directions  for  luting  iron,  glass,  or  earthenware 
retorts,  tubes,  etc.,  111.     Willis's  composition,  112.     Iron 
cement,  112.     Beale's  cement,   113.     Boiler  cement,  113. 
Bruyere's  cement,  113.     Oxy chloride  of  zinc  cement,  113. 
Crucibles        .  .  .  .  .  .  .         .113 

London    crucibles,    113.     Cornish   crucibles,    114.     Hessian 
crucibles,    114.      Plumbago   or    graphite    crucibles,     114. 
Patent  Plumbago  Crucible  Company's  crucibles,  115.  Stour- 
bridge  crucibles,  115.     Porcelain  crucibles,  115.     Qualities 
to  be  possessed  by  crucibles,  115.     Black-lead  crucibles, 
116.    Earthenware  crucibles,  116.    Charcoal  crucibles,  119. 
Lime  crucibles,  121.     Mr.  David  Forbes's  experiments  on 
crucibles,   122.     Alumina  crucibles,    123.     Magnesia  cru- 
cibles and  bricks,  123.     Malleable  iron  crucibles,  126.    Pla- 
tinum crucibles,  126.     Fresenius's  directions  for  preserving 
platinum  crucibles,  127,  131.     Mr.  Dexter's  lamp  for  pla- 
tinum crucibles,  1 28.     Erdmann's  explanation  of  the  grey 
coating  formed  on  platinum  crucibles,  129.     Cleaning  pla- 
tinum crucibles,  131.     Silver  crucibles,  133. 
Cupels        .  ....     133 

Mould  for  making  cupels,  134. 
Scori6ers    .  .  .  .  .  .  .  .136 

Methods  of  measuring  the  heat  of  furnaces  .  .  .136 

Pyrometers,  136.  Daniel's  pyrometer,  137.  Wilson's  pyro- 
meter, 139.  Siemens's  pyrometer,  140.  Plan  for  comparing 
the  temperatures  of  two  furnaces,  141. 


CHAPTER  V. 

Fuel,  its  assay  and  analysis  .  .  .  .  .  .142 

External  appearance  of  the  fuel,  its  porosity,  compactness,  fracture, 
size,  and  shape  of  pieces  .  .  .  .  .  144 


CONTENTS. 

PAGE 

Determination  of  the  adhering  water          .  .  .  .144 

Determination  of  the  specific  gravity  .  .145 

Determination  of  the  absolute  heating  power          .  .  .146 

Pyrometric  heating  power,  146.     Different  methods  of  ascer- 
taining the  absolute  heating  power,  1 46.    Berthier's  method , 
147.    Tire's  method,  149.    lire's  calorimeter,  150.    Wright's 
calorimeter,  151. 

Determination  of  the  specific  heating  power  ,          •<<":-         .     153 

Determination  of  the  pyrometric  heating  power     .          ^.         •*.  «     153 
Determination  of  the  volatile  products  of  carbonisation  *"."''     '    .,     154 
Examination  of  the  coke  or  charcoal  left  behind  on  carbonisation  .     155 
Determination  of  the  amount  of  ash  .  .  .;"'•  .     155 

Determination  of  the  amount  of  sulphur     .  .  .  .156 

Examination  of  other  peculiarities  of  fuel  .  *  .  .158 

Calculation  of  results          .  .  .  .  .  .158 

Assay  of  coal  before  the  blowpipe  .  .  .  .  .158 

Valuation  of  coal  for  the  production  of  illuminating  gas     .  .161 


CHAPTER  VI. 

Reducing  agents     .  .  .  .  -  .  .163 

Hydrogen  gas,  163.  Carbon,  164.  Black-lead  or  graphite, 
164.  Determination  of  the  value  of  graphite,  164.  An- 
thracite, 165.  Coke,  165.  Wood'  charcoal,  165.  The 
fatty  oils,  166.  Tallow,  166.  Resins,  166.  Sugar,  167. 
Starch,  167..  Gum,  168.  Tartar ic acid,  168.  Oxalic  acid, 
168.  Ammonium  oxalate,  168.  Comparative  reducing 
power  of  the  above  agents,  169.  Metallic  iron,  169.  Metal- 
lic lead,  170. 

Oxidising  agents     .  .  .  .  .  .170 

Oxygen,  170.  Litharge,  170.  Ceruse,  or  white  lead,  171. 
Action  of  oxide  of  lead  on  the  metals,  171.  Sulphur,  171. 
Selenium,  171.  Tellurium,  171  Arsenic,  171.  Anti- 
mony, 172.  Tin,  172.  Zinc,  173.  Bismuth,  173.  Iron, 
173.  Copper,  174.  Action  of  copper  oxides  upon  lead,  175. 
Lead  silicates  and  borates,  176.  Potassium  and  sodium 
nitrates,  176.  Assay  of  saltpetres,  177.  Gay- Lussac's  mode, 
177.  Foreign  substances  in  saltpetre,  178.  Lead  nitrate, 

180.  Manganese  peroxide,  180.     Copper  oxide,  180.    Iron 
peroxide,  180.     The  caustic  alkalies,  potash  and  soda,  180. 
Potassium  and  sodium  carbonates,  180.     Lead,  copper,  and 
iron  sulphates,  181.     Sodium  sulphate,  181. 

Desulphurising  reagents     .  f  .  .  .  .181 

The  oxygen  of  the  atmosphere,  181.     Charcoal,  181.     Iron, 

181.  Litharge,  182.     Its   behaviour  with   ordinary   sul- 
phides, 182.    Manganese  sulphide,  182.    Iron,  183.  Copper, 


CONTENTS.  XV11 

Desulphurising  reagents — continued. 

184.  Antimony,  185.  Zinc,  186.  Lead,  186.  Caustic 
alkalies  and  their  carbonates,  187.  Nitre,  saltpetre,  or  potas- 
sium nitrate,  188.  Lead  nitrate,  188.  Lead  sulphate,  188. 

Sulphurising  agents  .  .  .  .  .  .188 

Sulphur,  189.  Cinnabar,  189.  Galena,  189.  Antimony  sul- 
phide, 189.  Iron  pyrites,  189.  Alkaline  persulphides,  189. 

Fluxes        .  .  .  .  .  .      •»       .  .190 

Non-metallic  fluxes  .  .  .  .  .  .191 

Silica,  192.  Lime,  magnesia,  alumina,  and  their  silicates, 
192.  Glass,  192.  Borax,  192.  Analysis  of  glass,  193. 
Fluor-spar,  or  calcium  fluoride,  194.  Potassium  carbonate 
and  sodium  carbonate,  194.  Potassium  nitrate,  195.  Com- 
mon salt,  or  sodium  chloride,  195.  White  flux,  black 
flux,  and  raw  flux,  196.  White  flux,  197.  Black  flux, 
197.  Argol,  cream  of  tartar,  or  potassium  bitartrate,  198. 
Salt  of  sorrel,  or  potassium  binoxalate,  199.  White  or 
mottled  soap,  199.  Keducing  power  of  the  various  fluxes, 
199. 

Metallic  fluxes        .  .  .  .  .  .  .200 

Litharge  and  ceruse,  200.  Glass  of  lead,  or  lead  silicate,  200. 
Lead  borate,  201.  Lead  sulphate,  201.  Copper  oxide,  201. 
The  iron  oxides,  201. 

CHAPTER  VII. 

The  blowpipe  and  its  use    ......     202 

Blowpipe,  203.     Nipples,  204.     Construction  and  material  for 
jets,  20o.     Flame,  205.     Faraday's  directions  for  using  the 
blowpipe,  206.     Oxidation,  209.     Reduction,  209. 
Auxiliary  blowpipe  apparatus         .  .  .  .  .210 

Supports,  210.     Charcoal,  210.     Platinum,  211.     Wire,  211. 
Platinum    spoon,    212.     Ross'    support,    212.     Hartley's 
support,  213. 
Reagents  and  fluxes  .  .  .  .  .213 

Blue  litmus  paper,  213.    Reddened  litmus  paper,  213.   Brazil- 
wood paper,  213.     Turmeric  paper,  213.     Nitric  acid,  213. 
Zinc,    213.      Copper,    213.     Iron   wire,  213.      Potassium 
cyanide,  214.     Sodium  carbonate,  214. 
Fusion  of  substances  with  soda       .  .  .  .  .215 

Reduction  of  metallic  oxides  .  .  .  .216 

Borax,  218.  Sodium  ammonia- phosphate,  219.  Potassium 
nitrate,  220.  Potassium  bisulphate,  220.  Sodium  bisul- 
phate,  221.  Vitrified  boracic  acid,  221.  Cobalt  nitre,  221. 
Nickel  oxalate,  221.  Copper  oxide,  221.  Silica,  222. 
Turner's  flux,  222.  Calcium  fluoride  and  lime  sulphate, 
222.  Bone  ashes,  222.  Proof  lead,  223.  Tin  foil,  223. 
Dry  silver  chloride,  223.  Soda  paper,  227. 
a 


CONTENTS. 

PAGE 

General  routine  of  blowpipe  operations       .  .  .  .228 

Size  of  the  assay,  228.     Order  of  the  operations,  229. 

Discrimination  of  minerals .  .  .  .  •  .231 

Crystalline  form,  232.     Mode  of  fracture,  233.     Lustre,  233. 
Colour  and  streak,  234.     Hardness,  234.     Specific  gravity, 
236.      Fusibility,  238.      Chemical  characters,   239.      Re- 
.  quirements  for  testing  minerals,  243. 

Description  of  minerals       .    .         .  .  •  •  .243 

Quartz  and  the  silicates,  243.    Quartz,  244.    Rock  crystal,  244. 
Amethyst,  244.     Rose  quartz,  244.     Cairngorm,  or  smoky 
quartz,  244.     False  topaz,  244.     Chalcedony,  244.     Carne- 
lian  and  sard,  245.     Agate,  245.     Onyx  or  sardony,  245. 
Flint  or  hornstone,  245.     Jasper,  245.     Bloodstone,  245. 
Opal,   245.     Talc,  245.     Chlorite,   246.     Serpentine,  246. 
Augite  and  hornblende,  246.     Chrysolite  or  olivine,  247. 
Tourmaline,   247.     Garnet,   248.     Topaz,   248.      Beryl  or 
emerald,    249.     Zircon   or  hyacinth,  249.      Felspar,  249. 
Mica,  250.     Zeolites,  250.     Corundum  or  sapphire,  250. 
Spinel,  251.     Chrysoberyl,  252.    Diamond,  252.    Graphite, 
or  bla-ck  lead,  253.     Coal,  253.     Apatite,  253.    Fluor,  254. 
Calc-spar  or  calcite,  254.    Magnesite,  255.    Dolomite,  255. 
Aragonite,  255.     Rock  salt,  256.     Soluble  sulphates,  256. 
Nitre,  256.     Gypsum,  selenite,  or  alabaster,  256.     Heavy 
spar    or    barytes,    257.      Sulphur,    257.      Tin    ore,    257. 
Molybdenite,  258.  Bismuth,  258.  Antimony  sulphide,  258. 
Arsenic,  259.     Arsenic  sulphide,  259.     Native  iron,   259. 
Iron  pyrites,  260.     Arsenical  pyrites  or  mispickel,    260. 
Magnetic  iron,  260.     Specular  iron,  hematite,  or  micaceous 
iron,   261.     Red  ferric  oxide  or  red  ochre,  261.     Brown 
ferric  oxide,  or  yellow  or  brown  ochre,  261.     Titanic  iron, 
262.     Chromic  iron,  262.     Green-earth,  262.     Iron  carbo- 
nate, 263.     Manganese  ores,  263.     Arsenical  nickel,  263. 
Smaltine  or  tin-white  cobalt,   264.      Cobalt  bloom,   264. 
Blende,    264.      Zinc  carbonate  or  calamine,   265.     Zinc 
silicate  or  smithsonite,  265.     Galena,  265.     Lead  carbonate 
or  cerusite,  266.     Lead  sulphate  or  anglesite,  266.     Pyro- 
morphite  or  lead  phosphate,  266.     Cinnabar,  267.     Native 
mercury  or  quicksilver,  267.    Native  cop  per,  268.    Vitreous 
copper,  268.    Copper  pyrites,  268.   Grey  copper,  269.  Black 
cupric  oxide,  269.  Red  cuprous  oxide,  269.  Copper  carbonates, 
blue  and  green,  270.     Platinum,  270,     Gold,  271.     Silver, 

271.  Sulphide  of  silver,  271.     Antimonial  and  arsenical 
silver  ores,  272.     Horn  silver,  272.     Lead  and  antimony 
sulphides,  272.     Mercury,  lead,  silver,  or  copper  selenide, 

272.  Millerite  or  nickel  sulphide,  273.    White  nickel,  273. 
Rutile,  273.     Sphene,  273.     Wolfram,  273.    Pitchblende, 
274.     Magnetic  iron  pyrites,  274. 


CONTEXTS.  XIX 


Determination  of  minerals .  *  t  .  .  t  ;  «  .  274 

Scheme  for  the  determination  of  minerals  .  .  ,  .275 

Group  I.  Minerals  which  have  a  metallic  lustre,  and  which  give 

off  sulphur  .  .  .  .  .  .  .     277 

Group  II.  Minerals  which  have  a  metallic  lustre,  and  which  give 

off  either  an  odour  of  garlic  without  sulphur,  or  white  fumes 

which  have  not  a  garlic  or  sulphurous  odour  .  .279 

Group  III.  Minerals  which  have  a  metallic  lustre,  and  which  give 

off  no  fumes  ......     280 

Group  IV.  Minerals  which  possess  a  non-metallic  lustre,  a  coloured 

streak,  and  which  give  off  fumes  or  odour  when  heated 

before  the  blowpipe  .  .  .  .  .  281 

Group  V.  Minerals  which  possess  a  non-metallic  lustre,  a  coloured 

streak,  but  which  give  off  no  fumes  or  odour  before  the 

blowpipe      .......     282 

Group  VI.  Minerals  which  have  a  non-metallic  lustre,  and  which 

are  scratched  by  quartz,  showing  a  white  streak  .  .  283 

Group  VII.  Minerals  which  have  a  non-metallic  lustre,  and  which 

are  not  scratched  by  quartz  .  .  .  .287 

Coloured  flames       .......     290 

Blue  flames,  290.  Green  flames,  290.  Yellow  flames,  290. 

Red   flames,  290.     Chlorine,  290.     Lead,   291.     Arsenic, 

291.  Selenium  and  antimony,  29-1.    Bromine,  291.    Boracic 
acid,   291.     Tellurium,    291.      Copper,    291.     Iodine   and 
copper,  291.     Phosphoric  acid,  292.     Baryta,  292.     Zinc, 

292.  Soda,    292.     Water,   292.     Strontia,  292.      Lithia, 
292.     Lime,  292,    Potash,  292. 

CHAPTER  VIII. 

Volumetric  analysis  .  .  .  .  .  .293 

Reactions  of  volumetric  analysis,  293.  Principle  of  volumetric 

analysis,  293.     Standard  solutions,  295,  297. 
Instruments  and  apparatus,  297.     The  burette,  297.     Mohr's 
burette,  297.    Gay-Lussac's  burette,  299.    Brit-ton's  burette, 
300. 
Modes  of  operating,   300.     The   pipette,    301.      Measuring 

flasks,  302. 
Colorimetric  analysis          ,  302 

CHAPTER  IX. 

Assay  of  Iron         .......     303 

Ores  of  Iron  .  .....     303 

Metallic  iron  ore,  303.  Red  haematite,  303.  Brown  haema- 
tite, 303.  Spathic  iron  ore,  303.  Titaniferous  ore,  303. 
Franklinite,  303. 

a  2 


XX  CONTENTS. 

PAGE 

Assay  of  iron  in  the  dry  way          ...  .  .  .     304 

Classification  of  iron  ores,  304.     Fluxes,  305.     Air-furnaces, 
306.     Crucibles,  306.     The  charge,  308.     Ores  of  unknown 
composition,   308.     Ores  previously  analysed,    309.      The 
operation,  310. 

Effects  produced  by  the  following  substances  .  .  .312 

Manganese,  312,  313.     Titanium,  312,   313.     Phosphorus, 
313.     Sulphur,  313.     Chromium,  313. 
Calculation  of  results          .  .  .  .  •.  .     314 

Assay  of  iron  and  its  ores  in  the  wet  way  .  .  „  -  ^     317 

Dr.  Penny's  process  .  .  .  .  .  v».    317 

Titration  of  iron  by  tin  protochloride          .  .  ..-          .     322 

Fresenius's  experiments,  323.     Conditions  to  ensure  accurate 

result,  324.     Messrs.  Stock  and  Jack's  process,  325. 
Complete  assay  of  iron  ores  .  .  .  .  .326 

Determination  of  silica,  iron  oxide,  and  manganese  oxide,  326. 
Water-bath,  327.  Determination  of  lime  and  magnesia  and 
part  of  the  phosphoric  acid,  328.  Treatment  of  the  pre- 
cipitate, 329.  Treatment  of  the  alkaline  solution  poured 
off  from  the  first  black  precipitate ;  determination  of  alu- 
mina and  remainder  of  phosphoric  acid,  330.  Determina- 
tion of  potash  and  soda,  331.  Determination  of  sulphur, 
331.  Determination  of  carbonic  acid,  332.  Determination 
of  water,  333.  Reduction  of  ferric  to  ferrous  salts,  334. 
Estimation  of  ferrous  oxide  in  the  presence  of  ferric  oxide, 
334.  Estimation  of  ferric  oxide  in  a  silicate,  336. 
Estimation  of  carbon,  sulphur,  silicon,  phosphorus,  &c.,  in  metallic 

iron  and  steel  .  .  .  .  .     337 

I.  Carbon,  337.     Estimation  of  the  total  carbon,  337.     Esti- 
mation of  the  graphite,  338.     Tosh's  process,  340.     Esti- 
mation of  combined  carbon,  341.     Britton's  modification, 
343.      Dingler's    opinion,    345.      Taylor's    improvement, 
345. 

II.  Estimation  of  sulphur  in  iron  and  steel,  346.     Eggertz's 
method,  346.     Some  experiments  which  deserve  mention, 
349.     Assay  of  lime  used  in  blast-furnaces,  352.     Brown's 
substitution,     353.        Piesse's     method,     353.       Morell's 
method,  &54. 

III.  Estimation  of  sulphur  in  iron  ores,  354. 

IV.  Estimation  of  silicon  in  iron  and  steel,  356. 

V.  Estimation  of  phosphorus  in  iron  and  steel,  364.     Precau- 
tions to  be  taken  for  accurate  results,  365.     Tosh's  method, 
265.     Noad's  precautions,  366. 

VI.  Estimation  of  manganese  in  iron,  366.     Riley's  instruc- 
tions for  the  determination  of  manganese  in  spiegeleisen, 
&c.,  368. 


CONTEXTS.  XXI 

PAGE 

Estimation  of  carbon,  &c.  in  metallic  iron  and  steel — continued. 

VII.  Estimation  of  manganese  in  manganiferous  iron  ores, 
369. 

VIII.  Estimation  of  iron,   370.     Mr.  Peter's  method,  371. 
Standard,  372.     Permanganic  acid,  372.     Mr.  Galbraith's 
process,  373. 

IX.  Estimation  of  titanium  in  iron,  374.     Tosh's  advice,  376. 
BettelFs  modification  of  Mr.  D.  Forbes's  process,  376. 


CHAPTER  X. 

Assay  of  copper      .......     380 

Classification  of  minerals  and  substances  containing  copper  «     380 

Class  I.  Sulphuretted  ores  or  products  with  or  without  sele- 
nium, antimony,  or  arsenic,  380.  Copper  glance,  38^. 
Chalcopyrite,  380.  Erubesoite,  380.  Bournonite,  380. 
Fahlerz,  380.  Covelline,  380.  Wolfsbergite,  380.  Domey- 
kite,  380.  Copper  regulus,  copper  speiss,  <fec.,  380. 

Class  II.  Oxidised  ores  and  products,  380.  Red  copper,  380. 
Malachite,  380.  Azurite,  380.  Cyanosite,  380.  Phos- 
phate of  copper,  380.  Arseniates,  380.  Chromate,  vana- 
date,  and  silicate  of  copper,  slags,  &c.,  380. 

Class  III.  Copper  and  its  alloys,  380. 
Classification  of  different  methods  of  assaying  copper  .  .381 

A.  Assay  in  the  dry  way,  381. 

a.  For  rich  ores  and  products  of  Class  I.,  381. 
English  copper  assay  .  .  .  .  .  .381 

Moissenet's  description,  381.  Ticketing  in  Cornwall,  381. 
De  la  Beche's  sketch  of  the  method,  382.  Division 
adopted,  382. 

Section  I.  Reactions,  383.  Two  kinds  of  assays — roasted  and 
raw  sample,  383. 

1.  Regulus,  384.     Pyrites,  384.     Very  poor  pyrites,  385. 
Variegated  copper  ore,  385.     Sulphide  of  copper,  385. 
Carbonated  minerals,  385.     Native  mixture,  385. 

2.  Calcining,  386. 

3.  Coarse  copper,  386. 

4.  Washings,  387. 

5.  Testing,  refinery,  388. 

6.  Slags  for  prill,  389. 

Section  II.  Manipulations,  390.  Crucibles  used  in  Cornwall, 
390.  Wind  furnace,  390.  Fusion  for  regulus,  392.  Cal- 
cining the  matt,  395.  Coarse  copper,  396.  Washings, 
396.  Testing  and  refining,  397.  Prill,  397. 

Section  III.  Some  minerals  and  substances  of  a  special  nature ; 


XXL1  CONTENTS. 

PAGE 

English  copper  assay — continued. 

influence  of  foreign  metals,  397.  Stanniferous  minerals, 
397.  Antimonial  minerals,  398.  Zinciferous  minerals,  398. 
Plumbiferous  minerals,  399.  Regulus  of  Chili.  399.  Slags 
of  copper,  399.  Old  copper,  399. 

Section  IY.  Summary  considerations — comparison  of  the  re- 
sults with  the  analysis  by  the  wet  way,  399.  Principal 
causes  of  loss  in  the  Cornish  method,  401.  Assay  of 
copper  in  the  dry  way,  401. 

(B.  Assays  of  copper  in  the  wet  way  .  .  .  -.-402 

Colorimetric  copper  assays  .  .  .  .  .402 

Heine's  colorimetric  method,  403.  Examination  of  litharge, 
407.  M  tiller's  observation,  41 1.  Carnel ley's  colorimetric 
method,  41 1.  Solution  and  materials  required,  41 2.  Jacque- 
lain's  and  Von  Hubert's  colorimetric  assays,  413. 

Volumetric  copper  assays   .  .  .  .  •  .     417 

Fleck's  modification  of  Mohr's  method,  417.  E.  0.  Brown's 
method  by  sodium  hyposulphite,  421. 

Other  copper  assays  .  .  .  .  ^  .422 

Wolcott  Gibbs's  electrolytic  precipitation  of  copper  and  nickel, 
422.  J.  M.  Merrick's  method  of -assaying  copper,  423. 

Assay  of  copper  pyrites      .  .  .  .  .  -,424 

Determination  of  copper  and  sulphur  in  copper  pyrites,  426. 
Estimation  of  copper  in  the  Mansfield  ores  by  Dr.  Stein- 
beck's process,  427. 

1.  Extraction  of  copper  from  the  ore,  427. 

2.  Separation  of  the  copper,  428. 

3.  Quantitative  estimation  of  the   precipitated   copper, 
429.     Special  observations  on  this  method,  430. 

iEstimation  of  copper  by  M.  C.  Luckow's  process,  434.  Opera- 
tions, 436. 

1.  Roasting  the  ore,  436. 

2.  Solution  of  the  roasted  .product,  436. 

3.  Precipitation  of  the  copper,  437.     Time  occupied,  439. 

4.  Weighing  the  copper,  440. 

Chapman's  directions  for  the  detection  of  minute  traces  of 
copper ,in  iron  pyrites  and  other  bodies,  441.  J.  M.  Mer- 
rick's gravimetric  method,  442. 

CHAPTER  XI. 

.Assay  of  Lead         ...  .  .  .     444 

Classification  of  minerals  and  substances  containing  lead    .  ,444 

.Assay  of -substances  of  the  first  class  (sulphides,  antimonial)  .     444 

The  action  of  various  substances  on  sulphides  of  lead  : — 
Action  of  oxygen,  444.    Action  of  metallic  iron,  444.    The 
alkalies  and  alkaline  carbonates,  445.    Potassium  nitrate, 
445.     Argol,  445. 


CONTEXTS.  XX111 

Assay  of  substances  of  the  first  class,  <fec. — continued.  PAGE 

Processes  generally  adopted  : — 

1.  Fusion  with  potassium  carbonate,  446. 

2.  Fusion  with  black  flux,  452. 

3.  Fusion  with  metallic  iron,  453. 

4.  Fusion  with  sodium  carbonate,  or  black  flux  and  metallic 

iron,  456. 

5.  Roasting  and  reducing  assay,  457. 

6.  Assay  with  sulphuric  acid,  459. 

7.  Assay  of  galena  in  the  wet  way,  460. 

Assay  of  substances  of  the  second  class       .  .  .  .463 

Humid  assay  of  ores  of  the  second  class      .  .  .  .466 

Assay  of  substances  of  the  third  class         .  .  .  .467 

Humid  assay  of  substances  of  the  third  class          .  .  .468 

Maxwell   Lyte's  process,    469.      Mascazzini's   process,   469. 

Jannesay's  process,  469. 
Alloys  of  lead  (Class  IV.) 470 

Assay  with  sulphuric  acid,  470. 
Additional  remarks  on  the  lead  assay         ....     470 

Comparison  of  the  different  methods  for  the  docimastic  deter- 
mination of  lead  in  their  application  to  various  products  .  470 

Martin's  comparative  experiments  : — 

a.  Assay  with  black  flux  and  iron,  470. 

b.  Roasting  and  reduction  assay  with  iron,  471. 

c.  Roasting  and  fusion  with  black  flux,  471. 
Results  obtained,  471. 

Level's  fusion  assay  with  potassium  ferrocyanide  and  cyanide        .     472 
Determination  of  lead  by  means  of  standard  solutions        .  .472 

1.  Flores  Dumonte's  method,  472. 

2.  Schwartz's  method,  473. 

3.  Buisson's  volumetric  process,  475. 

4.  Diehl's  volumetric  process,  476. 

5.  Mr.  M.  P.  Muir's  method,  477. 

CHAPTER  XII. 

Assay  of  tin  .......     478 

Tin  ores      .  .  .  .  .  .  .  .478 

Tin  oxide,  478.  Crystallised  tin  oxide,  478.  Disseminated 
tin  oxide,  478.  Sandy  tin  oxide,  478.  Concretionary  tin 
oxide,  wood  tin,  478. 

Analysis  of  a  sample  of  tin  oxide  from  Cornwall,  478. 
Remarks  on  tin  ore  and  the  minerals  which  may  be  mistaken 

for  it,  by  Dr.  A.  Leibius,  479. 

Assay  of  pure  tin  oxide      .  •  .  .  *  .  *     480 

Method  used  in  Cornwall,  481.     Method  by  means  of  potas- 
sium cyanide,  481. 
of  tin  oxide  mixed  with  silica  .          •   .  .     483 


Xxiv  CONTENTS. 

PAGE 

Assay  of  tin  ores  containing  silica  and  tin  slags      .  .  .483 

Assay  of  tin  ores  containing  arsenic,  sulphur,  and  tungsten  .     484 

Approximative  assay          ......     485 

J.  H.  Talbott's  method  for  assaying  tin  in  the  presence  of 

tungsten,  487. 

Estimation  of  tin  by  the  humid  method     .  . .  •"         -.    !         .     487 

Klaproth's  process,   487.     J.  B.  Hallet's  process,  489.     M. 

Moissenet's  process,  489. 
Assay  of  tin  in  gun  and  bell  metal  .  .  ,          •  .     490 

E.  Burse's  method,  491. 

Estimation  of  tin  by  means  of  a  standard  solution  .  .491 

M.  Gaultier  de  Clautry's  process,  491.  M.  Leressen's  process, 
492.  M.  Stromeyer's  process,  492.  Method  for  the  analysis 
of  tin  ore,  493.  Another  method,  494.  Decomposition  of 
tin  slags,  494.  MM.  Mohr  and  Terrell's  method,  495. 
Rammelsberg's  method,  495. 


CHAPTER   XIII. 

Assay  of  antimony  .  .  .  .  .  *  .  497 

Classification  of  antimonial  substances        .  .  .  .497 

Class  I.  Native  antimony  and  all  antimonial  substances  con- 
taining oxygen  or  chlorine,  but  little  or  no  sulphur  : — 
Native  antimony,  497.  Antimony  oxide,  497.  Antimo- 
nious  acid,  497.  Antimonic  acid,  497. 

Class  II.  Antimony  sulphide  and  all  antimonial  ores  contain- 
ing sulphur  : — Antimony  sulphide,  497.  Antimony  oxy- 
sulphide,  497.  Haidingerite,  497. 

Assay  of  ores  of  the  first  class         .  .  .  V        ••  .,    497 

Assay  of  ores  of  the  second  class     .  .  .  .  "       .   ..    498 

1.  Determination  of  the  pure  antimony  sulphide  (antimonium 

crudum)  .  .  .  .  '    .  ..     498 

2.  Determination  of  regulus  of  antimony        .  .  ..499 

Two  methods,  499. 

a.  By  roasting  and  fusing  the  oxidised  .matter  with 

black  flux,  499. 
5.  By  fusing  the  crude  ore  with  iron,  or  iron  scales, 

with  or  without  the  addition  of  black  flux,  499. 
F.  Becker's  method,  504.     Mr.  Sutton's  method,  504. 
Detection  of  antimony  in  sublimates          .  .  t  v    504 

To   distinguish  arseniuretted  hydrogen  from  an timoniu  retted  hy- 
drogen .  .  .  .  .  .  .505 

Separation  of  tin  from  antimony  and  arsenic          .  .  \     506 

C.  Winckler's  method,  506. 


CONTENTS.  .XXV 


CHAPTER  XIV.  PAGE 

Assay  of  zinc  „  .  .  .  .  .  .     508 

Classification  of  bodies  containing  zinc        ....     508 

Class  I.  Zinc  ores   in  which  the  metal  exists  as  oxide   not 
combined  with  silica,  508. 

Earthy  zinc   oxide,    508.      Manganiferous    zinc    oxide, 
508.     Zinc    aluminate,    Gahnite,    508.     Franklinite, 
508.      Anhydrous   zinc    carbonate,    508.      Hydrated 
zinc,  508. 

Class  II.  Zinc  ores  in  which  the  metal  exists  as  oxide,  but 
partly  or  wholly  combined  with  silica,  508. 

Anhydrous  zinc  silicate,   508.     Hydrated  zinc  silicate, 

electric  calamine,  508. 

Class  III.  Zinc  ores  in  which  the  metal  is  partly  or  wholly 
combined  with  sulphur,  508. 

Zinc   sulphide   (blende),  508.     Zinc   oxysulphide,  508. 

Zinc  sulphate,  508.     Zinc  selenide,  508. 
Class  IV.  AUoys,  508. 
Assay  of  ores  of  the  first  class         .....     508 

Determination  of  amount  of  zinc  by  the  humid  process  in  ores  of 

the  first  class  .......     512 

Assay  of  ores  of  the  second  class     .  .  .  .  .513 

Humid  determination  of  zinc  in  ores  of  the  second  class     .  .513 

Assay  of  ores  of  the  third  class       .  .  .  .  .514 

Humid  determination  of  zinc  in  ores  of  the  third  class        .  .514 

Alloys  (Class  IV.)  .  .  .  .  .  .515 

Volumetric  determination  of  zinc  .  .  .  .  .515 

Galetti's  process,  515.     Schaffher's  method,  modified  by  C. 
Kunzel,  517 

a.  Solution  of  the  ore,  and  preparation  of  the  ammoniacal 

solution,  517. 

b.  Preparation  and  standardising  of  the  sodium  siilphide 

solution,  518. 

c.  Determination   of    the   zinc   in   the   solution   of  the 

ore,  520. 

d.  Further  modification  of  the  process,  521. 

H.  Schwarz's  method,  522.     Carl  Mohr's  method,  523.     J. 
Drewson's  method,  524. 

CHAPTER  XV. 
Assay  of  mercury  .....  r  .     527 

Assay  of  mercurial  ores      .  .  .  .  .  .527 

Berthier's  method,  530.     Eschka's  method,  531. 

Assay  for  the  amount  of  cinnabar  in  an  ore  .  .  .532 

Volumetric  estimation  of  mercury  ....     533 

M.  J.  Personnel  method,   533.      M.  Rivot's  method,   536. 
G.  Attwood's  method,  536. 


XXvi  CONTENTS. 


CHAPTER  XVI.  PAGE 

Assay  of  silver       .  .  .  .  .  •  .538 

Classification  of  argentiferous  substances    .  .  .  .538 

Class  I.  Minerals  containing  silver,  538. 

Silver  glance,   538.      Brittle  silver   ore,  538.      Light  red 
silver  ore,  538.     Dark  red  silver  ore,  538.     Light  and 
dark  fahlerz,  538.     Argentiferous  copper  sulphide,  538. 
Polybasite,    538.      Slags,   538.      Cupel    bottoms,    538. 
Dross,  538.     Litharge,  &c.,  538. 
Class  II.  Metallic  silver  and  alloys,  538. 
General   observations   on  the  assay   of   ores    and   substances   of 

Class  I.  .  .  .  Y  .  /          .     538 

Fusion  with  oxidising  reagents        .  »  ,          .  .  .     541 

Litharge,  541. 
Special  directions  for  the  crucible  assay  of  ores  and  substances  of 

Class  I. 543 

Preliminary  assay  for  dividing  all  substances  of  this  class  into 
three  sections,  544.    Assay  of  reducing  power  of  argol,  545. 
Assay  of  oxidising  power  of  potassium  nitrate,  545.     Assay 
of  litharge  for  silver,  546. 

Assay  of  ores  of  the  first  section     .  .  -.'.-       ,.';C          •*-   ^^ 

Assay  of  ores  of  the  second  section  ^    •         .  ,  «     547 

Assay  of  ores  of  the  third  section    .  .  ,'        ,'."•"•  '•     547 

Scorification  .  .  .  .  .  "          «  .     548 

The  roasting,  550.     The  fusion,  550.     The  scorification,  550. 
Special  instructions  for  the  scorification  assay  of  ores  of  Class  I.    .     553 

Assay  in  scorifier,  553. 

Assay  of  substances  of  Class  I.  admixed  with  native  or  metallic 
silver      ........     554 

Cupellation  .  .  .  .  .         ;    .  .555 

Pliers  and  microscope,  560. 
Amalgamation        .  .  .  .  k  .  •     564 

Substances  of  the  second  class         .  .  .  .4  *     565 

Separation  of  silver  from  galena     .  .  •'..''       •.  %     565 

General  remarks  on  the  assay  of  the  alloys  of  silver  and  copper     .     565 
Cupellation,  565.     D'Arcet's  results,  566.     Quantity  of  lead 
required,    567.     Loss   of    silver   in   the   assay   of   coined 
alloys,  568. 

Special  instructions  for  the  assay  of  the  alloys  of  silver  and  copper     569 
Assay  for  approximative  quantity  of  alloy,  569.    Assay  proper 
of  silver  bullion,  569.    Assay  of  alloys  of  copper  and  silver, 
570. 

Alloys  of  platinum  and  silver         »  .  A  ,  .570 

Alloy  of  platinum,  silver,  and  copper        v  •  ...  .571 

Assay  of  native  silver,  rough  silver  left  on  sieve  during  pulverisa- 
tion of  silver  ores  of  first  class,  and  native  alloys  of  silver  «     571 


CONTEXTS.  XXV11 

PAGE 

Dr.  W.  Dyce's  process  for  separatiDg  gold   and  silver  from  the 

baser  metals        .  .  .«  .  .  .  •     571 

Assay  of  silver  bullion  by  the  wet  method  .  *  '.572 

Gay-Lussac's  method          .  .  .  .  .  .572 

Measurement  of  the  solution  of  common  salt,  574.     Measure 
of  the  normal  solution  of  salt  by  weight,  574.     Preparation 
of  the  decime  solution  of  common  salt,  576.     Preparation 
of  the  decime  solution  of  silver,  578.    Weighing  the  normal 
solution  of  common  salt,  578.    Preparation  of  the  normal 
solution  of  common  salt  when  measured  by  weight,  579. 
Preservation  of  the  normal  solution  of  common  salt,  584. 
Application  of  the  process  described  in  the  determination 
of  the  standard  of  a  silver  alloy,  585.     Correction  of  the 
standard  of  the  normal  solution  of  salt  when  the  tempera- 
ture varies,  587.     Table  of  corrections  for  variations  in 
temperature  of  the  normal  salt  solution,  589. 

Table  for  the  assay,  by  the  wet  method,  of  an  alloy  containing  any 
proportions  whatever  of  silver,  by  the  employment  of  a  constant 
measure  of  the  normal  solution  of  common  salt  .  .     589 

Tables  for  determining  the  standard  of  any  silver  alloy  by  employ- 
ing an  amount  of  alloy  always  approximatively  containing  the 
same  amount  of  silver     .....         592,  602 

Assay   of  pure,  or  nearly   pure  silver,  the   temperature  of  the 
normal  solution  of  salt  being  that  at  which  it  was  standardised     612 

First  example,  612.  Second  example,  613.  Third  example,  614. 
Graduation  of  the  normal  solution  of  salt,  the  temperature  being 
different  to  that  at  which  it  was  wished  to  be  graduated  .     615 

First  process,  615.     Second  method,  616. 

Approximative  determination  of  the   standard  of  an   unknown 
alloy       ........     616 

Modes  of  abridging  manipulation  .  .  .  .  .617 

Bottles,   617.     Stand,    618.     Water-bath,  618.      Flue,  619. 

Agitator,  619.     Table,  620.     Cleaning  the  bottles,  622. 
Reduction  of  silver  chloride  obtained  in  the  assay  of  alloys  by  the 
wet  method         .  .  .  .  .  .  .622 

Preparation  of  pure  silver  .  .  .  .  .  .623 

Modifications  required  in  the  assay  of  silver   alloys   containing 
mercury  .  .  .  .  .  .  .     624 

Method  of  taking  the  assay  from  the  ingot,  625.     Method  of 
assaying  silver  bars  adopted  in  the  assay  offices  of  H.M. 
Indian  mints,  625.    The  chloride  process,  626.    Apparatus 
and  appliances  required,  635. 
Titration  of  silver  in  presence  of  other  metals         .  .  .639 

Copper,  639.     Mercury,  639.     Palladium,  640. 

Determination  of  silver  in  galena  by  Volhard's  process      ~*  .     640 

David  Forbes  on  blowpipe  assay  of  silver  .  .  •  .641 

Apparatus,  642.     Concentration  of  the  silver  lead,  643.     Cu- 


XXV111  CONTENTS. 

David  Forbes  on  blowpipe  assay  of  silver — continued.  PAGE 

pellation,  645.  Determination  of  the  weight  of  the  silver 
globule  obtained  in  cupellation,  649.  The  scale  for  this 
purpose,  649.  Cupellation  loss,  653.  Table  modified  by 
Plattner,  654. 

Classification  of  argentiferous  substances    .  .  ,  .'  .655 

A.  Metallic  alloys  capable  of  direct  cupellation,  656. 

a.  Consisting  chiefly  of  lead  or  bismuth,  656. 

b.  Consisting  chiefly  of  silver,  and  alloys  of  silver  with 
gold  and  copper,  657. 

c.  Consisting  chiefly  of  copper,  658. 

B.  Metallic  alloys  incapable  of  direct  cupellation,  659. 

a.  Containing  much  copper  or  nickel,  with  more  or  less 

sulphur,  arsenic,  <fec.,  659.        . 
5.  Containing  tin,  660. 

c.  Containing  antimony,  tellurium,  or  zinc,  661. 

d.  Containing  mercury ;  amalgams,  663. 

e.  Containing  much  iron,  663. 

Alloys  of  silver  and  copper,  665. 


CHAPTER  XVII. 

Assay  of  gold         ....  .,/.       "  ..    .         .     666 

Classification  of  substances  containing  gold  •..+•.  .•         .."  -          .     666 

Class  I.  Ores  containing  gold,  666.     Graphite  tellurium,  666. 

Folliated  tellurium,  666. 
Class  II.  Alloys  of  gold,  666.     Native  gold  and  aurides  of 

silver,  667.     Artificial  alloys  of  gold,  667. 
Assay  of  gold  ores .  .  .  .  .  .  667 

Preparation  of  the  sample,  668.  Collection  of  the  gold  and 
silver,  668.  Crucible  assay,  668.  The  charge,  669.  Size 
of  lead  button,  669.  Cupellation,  669.  Preliminary  assay 
of  ore,  670.  Charge,  670.  Crucible,  670.  Ores  to  be 
roasted,  671.  Roasting  the  ore,  671.  Fusion,  673.  Scori- 
fication  assay,  673.  The  lead  button,  675.  Cupella- 
tion, 675. 

General  observations  on  the  assay  of  gold  ores  .  ,,  •  ...  '  .  679 
Gold  and  copper,  proportion  of  lead,  679.  Examination  on 
the  touchstone,  680.  Table  for  the  proportion  of  lead  to 
be  employed  in  the  cupellation  of  gold  and  copper,  681. 
Gold,  silver,  platinum,  and  copper,  682.  Gold  alloyed  with 
silver,  683.  Inquartation,  684.  Operation,  684.  Sur- 
charge, 685.  Makin's  method,  686.  Aqua  regia,  687. 
Von  Juptner's  method,  688.  Another  method,  688. 

Standard  of  the  alloys  of  gold      . •*,  .       ......  689 


CONTEXTS. 


PAGE 

Assay  of  gold  coin  and  bullion      ...          *  .  ,  .     689 

Preliminary  assay,  689.    Assay  proper,  690.     Parting  assays, 

692 

Assay  of  pyrites  for  gold    .  .  .  .  .  V    694 

Detection  of  minute  traces  of  gold  in  minerals        .  .  .     696 


CHAPTER  XVIII. 

Assay  of  platinum .  .  .  .  .  .  .     700 

Platinum  in  its  native  state  .....     700 

Analysis  of  platinum  ores  .  .  .  .  .  .701 

Bunsen's  method,  701.  Platinum  and  palladium,  701.  Ru- 
thenium, rhodium,  and  iridium,  704.  C.  Lea's  process, 
709.  Deville  and  Debray's  process,  714.  Sand,  714.  Os- 
miridium,  715.  Platinum  and  iridium,  716.  Palladium, 
iron,  and  copper,  717.  Gold  and  platinum,  718.  Rhodium, 

718.  Analysis  of  platinum   ores   from   various   sources, 

719.  Guyard's  process  for  extracting  metals  from  platini- 
ferous  residues,  719.    Analysis  of  osmiridium,  722.    Wol- 
cott  Gibbs's  process,  723.     Nelson  Perry's  process,  726. 

CHAPTER  XIX. 
Assay  of  bismuth   .......     728 

Varieties  of  bismuth  ores  .  .  .  .  .  .728 

Native  bismuth      .  .  .  .  .  .  .728 

Assaying  bismuth  ores        .  .  .  .  .  .729 

Assaying  bismuth  in  ores  containing  a  large  amount  of  copper       .     729 
Refining  crude  bismuth      ......     732 

Purification  of  the  reduced  bismuth  ....     733 

Purification  of  bismuth  from  arsenic,   733.     Purification  of 
bismuth  from  antimony,  734.     Purification  of  bismuth  from 
copper,  734.     Purification  of  bismuth  from  sulphur,  735. 
Volumetric  assay  of  bismuth  .  .  .  .  .736 

R.  W.  Pearson's  process,  736.     M.  P.  Muir's  process,  737. 

CHAPTER  XX. 

Assay  of  chromium  .  .  .  .  .  .739 

Principal  ore  of  chromium  .  .  .  .739 

Analysis  of  it,  739. 
Assay  of  chrome  ore  .  .  .  .  .739 

Genth's   process,   739.     O'Neill's  process,   741.     W.  Gibbs's 

process,  742.     Clark's  process,  743. 

Determination  of  chromium  by  means  of  standard  solutions  .     744 

Determination  of  chromium  in  iron  and  steel,  745.  J.  0. 
Arnold's  process,  745.  Precautions,  747.  W.  J.  Sell's 
process,  747.  R.  Kayser's  process,  747. 


XXX  CONTEXTS. 


CHAPTER  XXI.  PAGE 

Assay  of  arsenic     .  .  .  .  .  .  .749 

Minerals  from  which  arsenic  is  produced    ....     749 

Assay  for  arsenic   .  ,          •  ?    •          «  ,         V  .  .     749 

Approximative  method,  749.     Improved  method,  749. 


CHAPTER  XXII. 

Assay  of  manganese  ....  -  ^  '          .     751 

Commercially  valuable  minerals  containing  manganese      .'_..          .     751 

Valuation  of  manganese  ores  .  .  .  %_  .751 

Sherer  and  Rumpfs  method,  752.  Mohr's  method,  753.  Otto's 

method,    754.      Bunsen's   method,    755.      J.    Pattinson's 

process,  755. 

CHAPTER  XXIIL 

Assay  of  nickel  and  cobalt  ores       .  .  ,  .  .757 

Ores  of  nickel         .  .  .  .  f  .          '.,     757 

Ores  of  cobalt          .  .  .  .  .  .  .757 

Hadow's  process  for  separating  nickel  and  cobalt  .  .  .     757 

Assay  of  nickel  ores  .  .  .  .  .  .761 

Assay  of  commercial  metallic  nickel  .  .  .  .     762 

Assay  of  cobalt  ores  .  .  .  .  .  .     762 

Liebig's  method  of  separating  nickel  and  cobalt      .  .  .     763 

Wolcott  Gibbs's  improvement         .  .  .  ".  .763 

Terrell's  method     .....  '.r  .     764 

Fleitmann's  quantitative  assay  of  small  proportions  of  cobalt  in 

nickel  .  .  .  .  .  .  .765 

Plattner's  method  for  detecting  nickel  before  the  blowpipe  .     766 

Assay  of  complex  nickel  and  cobalt  ores     .  .  .  .767 

A.  Olassen's  method,  767.     Alloys  of  zinc,  copper,  and  nickel, 

769. 

Ohl's  method  for  the  assay  of  nickel  speiss  1  .  i     771 

Lead  and  copper  speiss,  772.     Speiss  containing  little  or  no 

lead  or  antimony,  772.     Speiss  containing  much  lead  or 

antimony,  773. 

CHAPTER  XXIV. 

Assay  of  sulphur    .....  ,             .     775 

Commercially  valuable  sulphur  minerals     .             .  r            .     775 

Assay  of  iron  and  copper  pyrites    .              .             .  f             .775 

Assay  cf  sulphur  in  the  dry  way    .              .             .  .,^                  775 

Assay  of  sulphur  in  the  wet  way  .             .           :  .  .  ,r .-.           t     777 

Pearson's  method,  778.     Deutecom's  method,  780.  Holland's 

method,  781. 


CONTEXTS.  XXXI 


CHAPTER  XXV.  PAGE 

Discrimination  of  gems  and  precious  stones  .  .  .783 

Explanation   and   introduction,   783.      Principal  sources   of 

recognition,  783 
Colourless  stones    .......     783 

Diamond,  783.     Quartz,   787.     White  zircons,  788.     White 
sapphire,  789.     White  topaz,  789.     Comparative  table  of 
the  weights  of  colourless  stones,  791.      Use  of  the  table, 
791. 
Yellow  stones         .......     792 

Yellow   zircon,    792.      Yellow   sapphire,    792.      Cymophane 
(chrysoberyl),  792.    Yellow  topaz,  793.    Yellow  tourmaline, 
793.     Yellow  emerald,  794.     Comparative  table  of  weights 
of  yellow  stones,  796.     Yellow  quartz,  797. 
Brown  and  flame-coloured  stones    .  .  .  .  .797 

Zircon  (hyacinth),    797.     Vermeil  garnet,  noble  garnet,  al- 
macdine,  797.     Comparative  table  of  weights  of  brown  or 
flame-coloured  stones,  798.     Essonite,  cinnamon  stone,  799. 
Tourmaline,  799. 
Red  and  rose-coloured  stones  .  .  .  .  .799 

Red  sapphire,  oriental  ruby,  799.     Deep  red  garnet,  noble 
garnet,  799.     Spinel  ruby,  799.     Reddish  topaz,  800.     Red 
tourmaline,  800.     Comparative  table  of  weights  of  red  and 
rose-coloured  stones,  800. 
Blue  stones  .  .  .  .  .  .  .801 

Blue  sapphire,  801.    Disthene,  cyanite,  801.    Blue  topaz,  801. 
Blue  tourmaline,  802.     Blue  beryl,  802.     Dichroite,  water 
sapphire,  802.     Turquoise,  802.     Comparative  table  of  the 
weights  of  blue  stones,  803. 
Violet  stones  .......     803 

Violet   sapphire,    803.      Violet    tourmaline,    803.      Violet 
quartz,  amethyst,  803.     Comparative  table  of  weights  of 
violet  stones,  804. 
Green  stones  .......     804 

Green  sapphire,  804.     Peridot  crysolite,  804.     Green  tourma- 
line, 805.      Emerald,   805.      Aqua-marine,  805.     Chryso- 
prase,  805.     Comparative  table  of  weights  of  green  stones, 
806. 

Stones  possessing  a  play  of  colours  (chatoyant)       .  .  .     806 

Sapphire,  807.     Garnet,   807.      Cymophane,  807.     Antique 
emerald,    807.      Quartz,   807.      Felspar,  nacreous  felspar, 
fish -eye,  &c.,  808.     Comparative  table  of  weights  of  stones 
possessing  a  play  of  colours  (chatoyant),  808. 
Glass  and  artificial  gems     ......     809 

Inferior  brilliancy,  809.  Inferior  hardness,  809.  Fusibility,  809. 


XXX11 


CONTEXTS. 


APPENDIX. 

TABLE  I.  Showing  the  quantity  of  fine  gold  in  1  oz.  of  any 
alloy  to  £  of  a  carat  grain  of  the  mint  value 
of  1  oz.  of  each  alloy  .  .  .  * 

TABLES  A,  B,  and  C.  To  convert  mint  value  into  bank  value 
when  the  standard  is  expressed  in  carats, 
grains,  and  eighths  .... 

TABLE  II.  Table  of  relative  proportions  of  fine  gold  and 
alloy,  with  the  respective  mint  values  of  1  oz. 
of  each  alloy  when  the  standard  is  expressed 
in  thousandths  .  .r  ..  '  V 

TABLE.  To  convert  mint  value  into  bank  value  when  the 
standard  is  expressed  in  thousandths  . 

TABLE  III.  Assay  table,  showing  the  amount  of  gold  and 
silver,  in  ounces,  pennyweights,  and  grains, 
contained  in  a  ton  of  ore,  &c.,  from  the 
weight  of  metal  obtained  in  an  assay  of  200 
grains  of  mineral  .  .  •  . 


PAGE 


11 


XX 


XX1-XXX11 


XXX111 


xxxiv-xlvii 


INDEX 


xlix 


A  MANUAL 


OF 


PRACTICAL   ASSAYING. 


CHAPTER  I. 

CHEMICAL   NOMENCLATURE LAWS   OF   COMBINATION,    ETC. 

IN  a  treatise  intended  to  be  used  principally  by  the  practical 
assayer,  it  is  neither  necessary  nor  practicable  to  give  more 
than  a  brief  outline  of  the  elements  of  chemical  nomencla- 
ture, and  of  chemical  combination.  A  knowledge  of  prac- 
tical chemistry  is  undoubtedly  of  great  value  to  the 
assayer  ;  indeed,  no  one  can  attain  to  any  degree  of  emin- 
ence in  this  branch  of  industry  unless  he  has  had  some 
amount  of  practice  in  the  laboratory ;  but  it  will  be 
beyond  the  scope  of  this  volume  to  teach  the  elements  of 
chemistry.  Such  instruction  in  chemistry  must  be  sought 
for  in  books  which  are  specially  devoted  to  the  science. 
The  student  should,  above  all,  endeavour  to  acquire  a 
practical  knowledge  of  experimental  chemistry  by  going 
through  a  course  of  lessons  in  a  laboratory. 

CHEMICAL  NOMENCLATURE. — Every  material  substance  with 
which  we  are  acquainted  consists  of  one  or  more  bodies, . 
termed  elements ,  from  the  fact  that  with  our  present  means 
of  research  we  are  unable  to  reduce  them  to  a  more  simple 
form.     Thus,  if  a  piece  of  common  iron  pyrites  be  exposed 


2  CHEMICAL   NOMENCLATURE. 

to  certain  chemical  operations,  it  will  be  found  to  consist 
of  two  substances,  both  physically  and  chemically  distinct 
from  each  other  and  from  the  original  substance.  One 
body  is  sulphur,  an  opaque  yellow  substance,  fusing  at  a 
very  low  temperature,  igniting  readily,  and  burning  with 
a  peculiar  suffocating  odour.  The  other  constituent  is  iron, 
a  well-known  metallic  substance,  requiring  an  intense  heat 
for  fusion,  and  not  burning  at  a  red  heat.  If  we  perform 
any  experiment  which,  in  the  present  state  of  knowledge, 
ingenuity  could  suggest,  we  are  totally  unable  to  cause 
either  the  sulphur  or  the  iron  to  assume  a  more  simple  or 
elementary  state  of  existence.  We  can  with  ease  cause 
either  of  them  to  enter  into  new  combinations  with  other 
bodies,  and  these  compounds  we  can  decompose — as  in  the 
case  of  the  pyrites — and  obtain  both  sulphur  and  iron  again 
in  their  separate  forms  with  all  their  characteristic  proper- 
ties ;  but  nothing  more  than  this  can  be  effected  :  hence 
we  are  led  to  the  belief  that  both  sulphur  and  iron  are 
elements,  or  bodies  containing  only  one  kind  of  matter. 

The  following  table  shows  the  elements  discovered  up 
to  the  present  time.  Those  substances  whose  names  are 
printed  in  italics  have  hitherto  found  no  practical  use ; 
and  those  marked  with  an  asterisk  (*)  are  often  found 
native,  or  unassociated  with  mineralising  elements. 


Non-metallic  Elements  or  Metalloids. 


Names  of  the 
Elements 

Symbols 

Atomic 
Weights 

Names  of  the 
Elements 

Symbols 

Atomic 
Weights 

Oxygen     . 
Hydrogen 

o 

H 

16 
1 

Selenium  .       '•    . 
Tellurium. 

Se 
Te 

79-6 
128 

Nitrogen 
Fluorine          :  «• 

N 
Fl 

14 
19 

Phosphorus 
Arsenic    . 

P 

As 

31 

75 

Chlorine 

01 

35-5 

*Carbon     . 

0 

12 

Bromine 

Br 

80 

Boron       .   1   . 

B 

11 

Iodine 

I 

127 

Silicium   . 

Si 

28-5 

*Sulphur 

S 

32      • 

Zirconium 

Zr 

90 

CHEMICAL   NOMENCLATURE. 


Metallic  Elements. 


Names  of  the 
Elements 

Symbols 

Atomic 
Weights 

Names  of  the 
Elements 

Symbol* 

Atomic 
Weights 

Potassium 

K 

39-1 

i  Cobalt 

Co 

58-8 

Sodium     . 

Na 

23 

Nickel 

Ni 

58-8 

Lithium    . 

Li 

7 

Zinc. 

Zn 

65 

Caesium    . 

CB 

133 

Cadmium 

Cd 

112 

Rubidium 

Rb 

85-4 

•Copper 

Cu 

63-5 

Barium     . 

Ba 

137 

Lead 

Pb 

207 

Strontium 

Sr 

87-5 

'   Thallium 

Tl 

204 

Calcium    . 

Ca 

40 

Indium 

In 

74 

Magnesium 
Aluminium 

s 

24 
27-5 

•Bismuth  x 
Tin  . 

Bi 

Sn 

208 
118 

Glucinum. 

Be 

14 

Titanium 

Ti 

50 

Cerium     . 

Ce 

92 

Tungsten 

W 

184 

Lanthanum 

La 

92 

Molybdenum 

Mo 

92 

Didymium 

Di 

96 

Vanadium 

V 

51-2 

Yttrium  . 

Y 

68 

Antimony. 

Sb 

122 

Erbium     . 

Er 

•Mercury    . 

Hg 

200 

Terbium    . 

Tr 

•Silver 

108 

Niobium   . 

Nb 

97-6 

*Rhodium  . 

Rh 

104 

Tantalum 

Ta 

137-6 

•Palladium 

Pd 

106-5 

Thorium  . 

Th 

231-5 

•Platinum  . 

Pt 

197*4 

Manganese 

Mn 

55 

•Iridium     . 

Ir 

198 

Chromium 

Cr 

52-5 

*Ruthenium 

Ru 

104 

Uranium  . 

U 

120 

*  Osmium    . 

Os 

199 

Iron  . 

Fe 

56 

•Gold 

Au 

197 

The  first  column  contains  the  name  of  the  element ; 
the  second,  the  symbol,  in  which  all  chemical  changes  and 
decompositions  are  most  readily  understood  ;  and  the  third, 
the  atomic  weight.  These  atomic  weights  are  not  given 
beyond  the  first  place  of  decimals,  to  avoid  tedious  calcu- 
lation ;  for  all  practical  purposes  they  may  be  considered 
accurate.  Of  the  compounds  of  these  elements,  only  those 
will  be  discussed  which  are  likely  to  fall  under  the  notice 
of  the  assay er. 

The  principal  compound  bodies  with  which  the  assay  er 
will  have  to  deal  are  acids,  oxides,  salts,  and  binary  sub- 
stances containing  no  oxygen. 

When  a  body  combines  in  more  than  one  proportion 
with  oxygen,  that  compound  containing  the  least  oxygen 
takes  the  termination  ous,  that  containing  the  most  ic :  thus, 
sulphurous  acid,  sulphuric  acid  ;  arsenious  acid,  arsenic 
acid;  ferrous  oxide, ferric  oxide ;  mercurous  oxide, mercuric 

B    2 


4  CHEMICAL   NOMENCLATURE, 

oxide  ;  in  only  one  proportion  (or  when  they  form  only 
one  basic  oxide)  they  are  distinguished  by  the  termination 
ic,  as  potassic  oxide,  aluminic  oxide. 

OXIDES  are  binary  oxygen  compounds  :  they  may  be 
divided  into  three  series.  The  first  series  comprises  those 
oxides  which  do  not  possess  the  property  of  combining  with 
acids  to  form  salts — they  are  termed  indifferent  oxides ; 
the  second  contains  those  capable  of  uniting  with  acids- 
to  form  salts,  and  called  salifiable  oxides  or  bases;  the 
third  comprises  those  oxides  which  have  acid  characters,, 
and  form  salts  by  uniting  with  bases. 

When  an  elementary  body  combining  with  oxygen 
forms  but  one  oxide,  it  is  simply  called  the  oxide  of  the 
element.  Thus  we  say  zinc  oxide,  or  zincic  oxide. 

If  the  body  is  capable  of  combining  with  oxygen  in 
many  proportions,  the  words  proto-,  sesqui-,  bin-,  or  per-,, 
&c.,  precede  the  term  oxide,  to  express  the  progressive 
amounts  of  oxygen.  Most  metals  form  one  salifiable 
oxide,  and  many  of  them  have  two  ;  these  are  now  gener- 
ally distinguished  by  the  terminations  ous  and  ic,  in  the 
same  manner  as  are  the  acids.  Thus  we  have  protoxide  of 
lead,  iron,  copper,  tin,  &c. ;  sesquioxide  of  aluminium,  iron,, 
or  chromium,  &c.  ;  binoxide  or  peroxide  of  manganese, 
copper,  mercury,  &c.  ;  and  when  we  speak  of  them  as  sali- 
fiable bases,  ferrous  oxide,  and  ferric  oxide  ;  mercurous 
and  mercuric  oxide  ;  potassic  oxide  ;  aluminic  oxide.  Some 
metals  unite  with  oxygen  in  still  higher  proportions  ;  these 
compounds  are  almost  always  acids,  such  as  chromic  acid? 
stannic  acid,  antimonic  acid,  &c. 

SALTS  are  formed  when  an  acid  unites  with  a  base,  and 
usually  the  properties  of  the  acid  and  the  base  are  recipro- 
cally neutralised  ;  thus  an  acid  which  before  combination 
possesses  the  power  of  reddening  blue  litmus,  loses  it  on 
combining  with  the  base,  and,  in  like  manner,  a  base  which 
would  at  first  change  reddened  litmus  paper  to  blue  loses 
this  property  as  the  acid  saturates  it.  In  this  case  the 
acid  and  base  have  combined  to  form  a  salt. 

The  names  of  salts  are  governed  first  by  the  nature  of 
the  acid  ;  secondly,  by  the  salifiable  nature  of  the  base ; 


LAWS   OF    COMBINATION  6 

and,  thirdly,  by  the  proportions  in  which  the  acid  and  base 
are  combined.  Acids  terminating  in  ic  form  salts  ending 
in  ate.  Acids  terminating  in  OILS  form  salts  terminating  in 
ite ;  and  the  new  names  having  these  terminations  are 
added  to  the  name  of  the  oxide.  Thus  sulphuric  acid 
and  iron  protoxide  form  sulphate  of  iron  protoxide, 
ferrous  sulphate,  or,  more  commonly,  protosulphate  of 
iron;  arsenious  acid  and  iron  protoxide  form  arsenite  of 
iron  protoxide,  ferrous  arsenite,  or  protarsenite  of  iron ; 
nitric  acid  and  iron  sesquioxide  form  nitrate  of  iron  ses- 
quioxide  or  ferric  nitrate. 

When  the  salt  exists  in  the  neutral  state  its  name  is 
formed  as  above,  but  if  the  proportion  of  acid  is  greater 
than  in  neutral  salts,  it  is  termed  an  acid  salt :  thus 
bisulphate  of  potassium  is  sometimes  called  acid  sulphate 
of  potassium.  If,  on  the  other  hand,  the  base  is  in  excess, 
the  name  is  preceded  by  the  words  sub  or  basic :  thus, 
subacetate  of  lead  or  basic-acetate  of  lead. 

Binary  compounds  containing  no  oxygen  exist  very 
largely  in  nature,  and  it  is  from  them  that  the  greater 
part  of  our  copper,  lead,  silver,  &c.,  is  obtained. 

When  a  non-metal  combines  with  a  metal  to  form  a 
•compound  which  is  neither  acid  nor  basic,  its  name  is 
derived  from  the  non-metal  by  the  addition  of  the  termi- 
nation uret  or  ide.  The  latter  term  is,  however,  gradually 
displacing  the  former,  and  is  now  seldom  employed  except 
in  the  case  of  sulphur  compounds,  and  in  these  one  term 
is  as  often  used  as  the  other.  Thus  the  compounds  of 
sulphur  with  iron  and  chlorine  with  silver  are  respec- 
tively called  sulphuret  or  sulphide  of  iron,  and  chloride  of 
silver. 

If  a  non-metal  combines  with  a  metal  in  more  than 
one  proportion,  the  same  rule  is  followed  as  with  the 
oxygen  compounds  :  thus  we  have  iron  j9r0fo-sulphide,  iron 
sesqui- sulphide,  and  iron  fo'-sulphide  (ordinary  iron  pyrites 
or  mundic). 

Laws  of  Combination. — On  examining  the  compounds 
which  the  same  substances  afford  by  their  union  in 
different  proportions,  it  has  been  noticed  that  the  pro- 


6  LAWS  OF   COMBINATION. 

portions  of  the  elements  existing  in  each  compound  are 
definite  ;  a  certain  weight  of  one  substance  will  only  com- 
bine with  a  certain  weight  of  another  substance,  and  the 
lowest  combining  weight  of  any  of  the  elementary  bodies 
is  termed  its  atomic  weight,  and  is  represented  by  the 
numbers  in  the  third  column  of  the  table  of  elementary 
substances. 

As  before  stated,  all  substances  combine  in  fixed  or 
definite  proportions  ;  thus,  if  223  parts  of  oxide  of  lead  are 
analysed,  they  will  be  found  to  consist  of  207  parts  of 
lead  and  16  of  oxygen.  Again,  the  analysis  of  18  parts  of 
water  or  oxide  of  hydrogen  would  give  2  parts  of  hydro- 
gen and  16  of  oxygen  ;  now,  taking  hydrogen  as  unity,  we 
have  207  as  the  equivalent  of  lead,  and  16  as  that  of 
oxygen.  If  we  follow  oxygen  further  in  its  combinations, 
it  will  be  seen  that — 

16  parts  of  oxygen  combine  with  1  part  of  hydrogen. 
„      „  „  „          207       „         lead. 

„      „  „  „  40       „         calcium. 

„      „  „  „  118       „         tin. 

„      „  „  „  63-5    „         copper. 


The  above  numbers,  therefore,  represent  the  equivalents 
of  the  respective  elements. 

Again,  the  equivalent  of  sulphur  is  32,  and  this 
represents  the  weight  of  sulphur  which  will  combine  with 
the  above  weights  of  hydrogen,  lead,  calcium,  tin,  or 
copper  to  form  sulphides  of  the  respective  bases.  35'5 
parts  of  chlorine,  or  79'5  parts  of  selenium,  also  combine 
with  the  same  weights,  viz.  hydrogen  1,  lead  207,  &c., 
to  form  chlorides  and  selenides. 

Compounds  like  these  are  of  the  simplest  class,  and 
consist  of  single  equivalents  only  ;  there  are,  however, 
many  compounds  containing  more  than  two  equivalents, 
in  which  case  the  following  laws  are  followed. 

In  one  class  of  compounds  the  quantity  of  one  of  the 
constituent  elements  remains  constant,  while  each  new 
compound  is  formed  by  the  successive  addition  of  another 


CHEMICAL  SYMBOLS.  7 

atom  of  the  other  constituent  element ;  and  it  must  also 
be  borne  in  mind  that  no  element  will  combine  with  an- 
other in  less  than  its  atomic  weight.  Another  series  will 
commence  with  two  atoms  of  an  element  united  with  an 
uneven  number  of  atoms  of  another  element ;  thus  we 
can  have  binary  compounds  in  the  proportion  of  2  to  3,  2 
to  5,  or  2  to  7. 

The  atomic  weight  of  a  compound  body  is  the  sum  of 
the  atomic  weights  of  the  elements  forming  it :  thus 
sulphuric  anhydride  is  composed  of  one  atom  or  32  parts 
of  sulphur,  and  3  atoms,  or  48  parts,  of  oxygen ;  its  atomic 
weight  is  therefore  80.  The  atomic  weight  of  any 
compound  body  may  be  ascertained  by  adding  together 
the  atomic  weights  of  its  constituent  elements. 

Owing  to  the  invariable  law  of  the  constancy  of  chemi- 
cal compounds,  we  are  enabled  to  calculate  the  reaction 
which  occurs  between  two  or  more  bodies  when  decompo- 
sition takes  place  :  thus  174-2  parts  of  sulphate  of  potas- 
sium contain  80  parts  of  sulphuric  anhydride  and  94'2 
parts  of  potassium  oxide  ;  and  if  it  were  desired  to  obtain 
sulphate  of  lead  by  the  decomposition  of  nitrate  of  lead  by 
adding  to  it  the  above  quantity  of  sulphate  of  potassium, 
the  exact  amount  of  nitrate  of  lead  required  would  be 
readily  found  by  adding  together  the  equivalent  of  the 
elements  forming  nitric  acid  and  oxide  of  lead. 

CHEMICAL  SYMBOLS:  THEIR  EMPLOYMENT  AND  USES. — The 
symbol  of  an  element  standing  alone  signifies  one  atom 
of  that  element.  Thus :  S  implies  not  only  the  element 
sulphur,  but  32  parts  of  sulphur ;  a  small  figure  on  the 
right-hand  side  of  the  symbol  indicates  the  number  of 
atoms  to  be  represented  ;  thus,  S2  is  equal  to  two  atoms, 
or  64  parts  of  sulphur. 

Two  symbols  placed  thus,  FeS,  indicate  a  compound 
of  equal  equivalents  of  iron  and  sulphur.  Separation 
of  elements  by  the  sign  +  or  a  comma  is  employed  to 
show  the  union  of  two  compound  bodies  ;  thus  the  com- 
pound of  silver  sulphide  and  lead  sulphide  may  be  thus 
written:  AgS-fPbS,  or  AgS,PbS.  A  large  figure  on  the 
same  line  as  the  symbol,  and  on  its  left  side,  multiplies  the 


8  CHEMICAL   SYMBOLS. 

whole  of  the  symbols  to  the  first  comma  or  -f  .sign  :  thus, 
2AgS,PbS,  or  2AgS  +  PbS,  represents  a  compound  of 
two  atoms  of  silver  sulphide  with  one  of  lead  sulphide. 
If,  however,  it  be  thus  written,  2(AgS,PbS),  it  means  two 
atoms  of  the  whole  of  the  elements  which  are  inclosed  in 
the  brackets. 


PREPARATION    OF   THE    SAMPLE.  9 


CHAPTEE  H. 

PREPARATION    OF   THE    SAMPLE WEIGHING. 

THE  selection  and  preparation  of  the  sample  is  the  first 
and  most  important  operation  in  assaying.  It  is  of  little 
use  for  the  operator  to  ascertain  with  accuracy  the  per- 
centage of  every  individual  constituent  in  the  mineral 
operated  on,  if  his  sample  does  not  truly  represent  the 
average  of  the  ore.  It  should  be  borne  in  mind  that 
samples  of  mineral  are  generally  selected  for  their  richness, 
and  represent  the  most  favourable  portions  of  the  ore ; 
and  no  pains  should  be  spared  to  secure  a  sample  for 
analysis  which  will  truly  show  the  bulk  of  mineral  whose 
value  is  required  to  be  known. 

The  assayer  must  always  bear  in  mind  the  object  which 
his  experiments  have  in  view.  If  they  are  to  ascertain 
the  actual  percentage  of  one  or  more  constituents  existing 
in  a  certain  stone,  his  labours  are  comparatively  easy,  all 
that  is  required  being  to  reduce  the  whole  of  the  specimen 
to  the  finest  possible  state  of  division,  and,  having  well 
mixed  the  powder,  to  analyse  a  portion  of  it. 

But  if  it  is  desired  to  find  out  the  composition  of  a 
special  mineral  or  crystal,  the  greatest  possible  care  must 
be  taken  to  remove  the  whole  of  the  gangue  or  other  im- 
purities, and  to  obtain  for  analysis  those  portions  only 
which  represent  with  greatest  accuracy  the  pure  mineral. 
To  effect  this  the  surrounding  rock  is  first  removed  as 
carefully  as  possible,  and  then  the  specimen  is  crushed 
into  coarse  pieces  on  a  sheet  of  clean  paper.  By  means 
of  a  pocket  magnifier  and  a  pair  of  pincers,  clean,  typical 
pieces  of  the  mineral  are  then  to  be  selected  for  analysis, 


10  PREPARATION   OF   THE   SAMPLE. 

If,  however,  as  will  most  frequently  be  the  case,  the- 
object  of  the  assay  be  to  ascertain  the  average  value  of  a 
mineral  lode  or  heap  or  ore,  then  the  assayer  must  proceed 
differently.  The  portion  experimented  upon  must  truly 
represent,  in  the  respective  amounts  of  its  valuable  ma- 
terial, -gangue,  quartz,  and  earthy  matters,  the  whole  bulk 
of  that  of  which  it  professes  to  be  a  sample  ;  and  this 
having  been  secured,  the  whole  must  be  carefully  pow- 
dered and  passed  through  fine  sieves,  taking  care  that 
every  portion  of  the  mineral  goes  through.  If  this  be  not 
attended  to,  it  will  frequently  happen  that  the  few  grains 
left  out  are  sufficient  to  vitiate  the  whole  assay ;  this  is 
especially  apt  to  be  the  case  when  examining  ores  the 
valuable  ingredients  of  which  are  of  a  ductile  or  malleable 
nature,  such  as  auriferous  quartz.  In  this  case  it  fre- 
quently happens  that  the  great  bulk  of  gold  exists  in  the 
form  of  one  or  two  small  pieces,  and  these  being  flattened 
and  beaten  out  in  the  operation  of  powdering  will  almost 
certainly  be  left  upon  the  sieve.  In  cases  like  this  it  is 
better  to  collect  and  assay  such  pieces  separately,  and  esti- 
mate their  proportion  to  the  whole  weight  of  the  sample r 
than  to  attempt  to  powder  and  distribute  them  uniformly. 

The  ore  must  always  be  reduced  to  a  powder,  more  or 
less  fine,  according  to  the  nature  of  the  chemical  operation 
or  assay  to  which  it  is  to  be  subjected.  This  division  is 
effected  by  means  of  the  anvil,  hammer,  pestle  and  mortar, 
sieve,  method  of  elutriation,  or  other  means  generally  in 
use  for  the  preparation  of  any  fine  powder.  The  actual 
process  to  be  adopted  must  vary  according  to  the  nature 
of  the  different  bodies  under  examination.  In  some  cases 
simple  crushing  is  sufficient ;  in  others  the  ore  will  have  to 
be  pounded  in  a  mortar ;  whilst  occasionally  it  is  necessary 
to  reduce  it  to  the  very  highest  degree  of  fineness  by 
elutriation. 

There  is  another  operation,  which  is  as  strictly  mecha- 
nical as  are  the  above,  viz.  washing,  dressing,  or  vanning  a 
sample  of  ore,  the  end  and  aim  of  which  is  to  separate, 
in  a  suitable  vessel,  by  means  of  water  and  difference  of 
specific  gravity,  the  earthy  or  useless  and,  in  some  cases, 


PREPARATION    OF   THE    SAMPLE. 


11 


objectionable  portion  from  the  heavier  metallic  and  valu- 
able portion.  This  operation  is  almost  always  employed 
on  the  larger  scale  in  dressing  ores  for  the  smelter. 

The  tools  and  materials  employed  in  preparing  the 
sample  are  the  anvil  (and  stand),  vice,  hammer,  files,  cold 
chisel,  shears,  pestle  and  mortar,  steel-crushing  mortctir,  sieve, 
&c. 

THE  ANVIL  (fig.  1). — The  anvil  is  most  useful  in  size 
when  it  weighs  about  28  Ibs.;  but  one  of  14  Ibs.  will 

FIG.  i. 


suffice.  The  anvil  recommended  is  of  the  shape  usually 
employed  by  the  blacksmith. 

The  anvil-stand  is  constructed  of  stout  wood,  about 
two  inches  in  thickness,  and  forms  a  cube  of  about  two 
feet  square.  It  contains  three  or  four  drawers,  which 
serve  to  hold  the  hammers,  cold  chisel,  shears,  files,  &c., 
which  are  required  in  an  assay  office.  In  the  centre  the 
anvil  is  fixed,  and  in  one  corner  a  vice  may  be  also 
secured. 

In  general  the  anvil  and  hammer  are  employed  for  the 
purpose  of  breaking  a  small  fragment  from  a  mass  of  ore 
for  examination,  or  ascertaining  whether  the  button  or 
prill  of  metal  produced  in  an  assay  be  malleable  or  other- 


12  PREPARATION  OF  THE  SAMPLE. 

wise.  The  anvil  is  also  exceedingly  useful  as  a  support 
for  a  crucible  while  breaking  it  to  extract  the  metallic  or 
other  valuable  contents. 

THE  HAMMERS  (figs.  2  and  3),  of  which  two  are  requisite, 
FIG.  2.          FIG.  3.  ought  to  have  one  end  flat  and 

square  and  the  other  pick-  or 
wedge-shaped.  The  horizontal 
wedge  end  of  fig.  2  is  useful  for 
breaking  open  crucibles  and  in 
detaching  small  fragments  from 
a  specimen  of  ore.  The  flat  end 
serves  for  ascertaining  the  mal- 
leability of  buttons  of  metal. 
This  hammer  should  weigh  about 
1  Ib.  The  larger  hammer,  fig.  3, 
should  weigh  about  41bs.,  and  is 
employed  for  breaking  coke  suffi- 
ciently fine  for  the  use  of  the  fur- 
nace, and  detaching  fragments 
from  refractory  minerals,  in  both  of  which  cases  either 
end  may  be  employed,  as  may  seem  most  serviceable  to 
the  operator.  The  flat  end  of  this  hammer  is  also  used 
for  driving  a  cold  chisel  in  separating  masses  of  gold, 
silver,  copper,  lead,  &c.,  for  assay.  This  hammer  has  a 
vertical  pick  or  wedge  end. 

Very  hard  and  stony  materials  which  have  to  be  broken 
on  the  anvil  (and  all  such  ought  to  be  so  treated)  scatter 
many  fragments,  to  the  certain  loss  of  a  proportion  of  the 
substance,  and  the  probable  injury  of  the  operator ;  this 
can  be  prevented  by  wrapping  the  mineral  in  a  piece  of 
stout  brown  paper,  or  if  necessary  in  several  folds.  The 
fracture  can  then  be  safely  attempted. 

This  latter  precaution  must  be  specially  taken  in  frac- 
turing gold  quartz,  or  hard  rock  containing  metallic  silver, 
as  the  loss  of  a  very  minute  quantity  of  metal  would 
involve  a  considerable  error  in  the  result  afforded  by  the 
assay. 

All  minerals,  unless  very  friable,  must  be  reduced  to  a 
moderate  size — say  that  of  a  walnut — by  means  of  the 


PREPARATION   OP   THE   SAMPLE.  13 

anvil  and  hammer,  before  pulverisation  ;  otherwise,  if  the 
reduction  be  attempted  in  a  mortar,  it  is  nearly  certain  to 
be  injured ;  moreover,  the  operator  will  find  his  labours 
much  abridged  by  using  the  anvil  for  this  purpose. 

The  anvil  can  also  be  made  very  serviceable  in  repoint- 
ing  worn  or  burnt-out  tongs,  &c.  It  need  scarcely  be 
added  that  it  must  be  placed  as  far  as  possible  away  from 
bottles  or  other  frangible  articles,  otherwise  accidents  may 
occur  by  the  forcible  projection  of  fragments  of  crucibles, 
stones,  &c. 

THE  COLD  CHISEL  (fig.  4)  is  employed  for  cutting  off  me- 
tallic masses  for  assay.  It  should  be  five  or  six  inches  long, 
and  about  "half  an  inch  wide,  which  is  the  best  size  for 
general  use.  However,  for  some  purposes,  as  cutting  copper 
and  other  very  tough  metals,  it  is  convenient  to  have  a 

FIG.  4. 


chisel  only  a  quarter  of  an  inch  wide,  as  these  metals  are 
so  much  more  difficult  to  cut,  and  the  small  chisel  meets 
with  the  least  resistance. 

Small  shears  (fig.  5)  are  also  exceedingly  useful  in 
cutting  off  pieces  of  sheet  metal,  as  lead,  for  cupellation, 
scorification,  &c. 

THE  PESTLE  AND  MORTAR. — Mortars  are  made  of  various 
materials,  as  cast-iron,  bronze,  porcelain,  agate,  &c. ;  the 
assayer  requires  one  of  cast-iron,  one  of  porcelain,  and 
one  of  agate. 

The  iron  mortar  (fig.  6)  ought  to  be  of  the  capacity  of 
from  three  to  four  pints ;  the  porcelain  (Wedgwood  ware) 
(fig.  7)  may  contain  about  two  pints.  The  ease  with  which 
a  mortar  may  be  used  depends  much  upon  its  form,  and 
opinion  is  greatly  divided  on  the  subject.  Faraday  *  says 
that  the  pestle  should  be  strong,  and  the  size  of  its  upper 

*   Chemical  Manipulation,  p.  149. 


14  PREPARATION  OF  THE  SAMPLE. 

part  sufficient  to  allow  of  its  being  grasped  firmly  in  the 
hand,  and  below  to  permit  a  considerable  grinding  surface 
to  come  in  contact  with  the  mortar.  Its  diameter  in  the 
lower  part  may  be  about  one  third  or  one  fourth  of  the 
upper  diameter  of  the  mortar.  The  curve  at  the  bottom 
should  be  of  shorter  radius  than  the  curve  of  the  mortar, 
that  it  may  not  touch  the  mortar  in  more  than  one  part, 
whilst  at  the  same  time  the  interval  around  may  gradually 
increase,  though  not  too  rapidly,  towards  the  upper  part 
of  the  pestle. 

The  bottoms  of  all  mortars  ought  to  be  of  considerable 

FIG.  6.  FIG.  7. 


thickness,  in  order  to  withstand  the  smart  blows  they  will 
occasionally  have  to  receive. 

Berzelius  recommended  a  mass  of  pumice-stone  for 
cleansing  porcelain  mortars.  It  is  used  with  water  as  a 
pestle,  and  in  course  of  time  will  be  worn  to  the  shape  of 
the  mortar ;  its  action  will  then  be  more  speedy. 

Iron  mortars  can  be  best  cleaned  by  friction  with  a 
little  fine  sharp  sand,  if  washing  be  not  sufficient  to  re- 
move the  adhering  substance.  Great  care  must  be  taken 
to  dry  mortars  perfectly,  especially  those  of  iron,  other- 
wise they  will  become  rusted,  and  the  rust  will  contaminate 
the  substances  pulverised  in  them. 

The  iron  mortar  is  principally  of  use  in  the  reduction 
of  the  masses  of  mineral  (broken  on  the  anvil,  as  before 
described)  to  a  state  of  coarse  powder,  in  order  to  render 
the  substance  more  readily  capable  of  pulverisation,  strictly 
so  called.  In  the  use  of  the  iron  mortar,  all  friction  with 


PREPARATION   OF   THE   SAMPLE.  15 

the  pestle  ought  to  be  avoided,  and  the  body  within  it 
must  be  struck  repeatedly  and  lightly,  in  a  vertical  direc- 
tion, taking  care  to  strike  the  large  pieces,  so  that  all  may 
be  equally  reduced.  This  can  be  carried  on  until  the 
whole  is  about  the  size  of  fine  sand.  It  is  transferred  to 
the  porcelain  mortar,  where  direct  blows  must  be  carefully 
avoided. 

The  process  is  now  carried  on  somewhat  differently : 
the  pestle  is  to  be  pressed  with  a  moderate  force,  and  a 
-circular  motion  given  to  it,  taking  care  every  now  and 
then  to  lessen  and  then  to  enlarge  the  circles  so  as  to  pass 
over  the  whole  grinding  surface  of  the  mortar,  and  insure 
the  pulverisation  of  the  mass  of  mineral  submitted  to 
operation.  In  general,  the  finer  the  state  of  division  to 
which  a  mineral  is  reduced,  the  more  accurate  and  ex- 
peditious will  be  its  assay  ;  and  in  preparing  a  mineral  for 
assay  by  the  wet  method,  no  labour  ought  to  be  spared 
on  this  point.  Pulverisation  is  rendered  much  easier  by 
operating  on  a  small  quantity  at  once,  and  removing  it 
very  often  from  the  sides  and  bottom  of  the  mortar  by 
means  of  a  spatula.  The  quantity  operated  on  at  one 
time  must  be  regulated  by  the  hardness  and  friability  of 
the  substance  whose  pulverisation  is  to  be  effected.  The 
harder  it  is,  the  less  must  be  taken,  and  vice  versa. 

In  the  use  of  the  iron  mortar  fragments  are  occasionally 
projected.  This  may  be  prevented  by  covering  the  upper 
part  of  the  mortar  with  a  cloth.  This  applies  also  to  the 
porcelain  mortar,  for  the  dust  of  some  minerals  has  a 
•disagreeable  taste  and  smell.  Indeed,  in  some  cases  the 
ambient  powder  is  highly  deleterious,  as  in  the  pulverisa- 
tion of  arsenical  nickel,  cobalt,  and  other  ores.  Here  the 
simple  cloth  is  not  a  sufficient  protection ;  it  should  be 
slightly  damped  with  water,  and  tightly  tied  round  the 
mortar,  and  firmly  held  round  the  pestle,  when  nothing 
<3an  escape. 

Some  minerals  can  be  pulverised  with  greater  ease  if 
they  are  ignited  and  suddenly  quenched  in  cold  water. 
Amongst  them  may  be  named  flint,  and  many  other  sili- 
ceous matters,  as  gold  quartz.  In  the  pulverisation  of 


16 


PKEPAKATIOtf   OF   THE    SAMPLE. 


FIG.  8. 


charcoal  for  assays,  it  will  be  found  useful  to  heat  it,  as 
hot  charcoal  is  more  readily  pulverised  than  cold. 

In  some  instances  the  powder  obtained  in  the  iron  or 
porcelain  mortar  is  not  fine  enough  ;  recourse  should  then 
be  had  to  the  agate  mortar,  in  which  the  mineral,  in  as 
fine  a  state  of  division  as  the  larger  mortars  will  give  it,  is 
ground  in  small  portions  at  a  time,  until  it  is  reduced  to 
an  impalpable  powder. 

When  small  specimens  orrare  minerals  are  being  oper- 
ated upon,  if  it  is  especially  desirable  to  avoid  loss,  it  is 

advisable  to  use  a  steel  mor- 
tar (fig.  8)  for  the  prepara- 
tory reduction  of  the  mineral 
to  coarse  powder.  A  B  and 
C  D  represent  the  two  com- 
ponent parts  of  the  mortar  ; 
these  may  be  readily  taken 
asunder.  The  substance  to 
be  crushed  (having,  if  prac- 
ticable, first  been  broken  into 
small  pieces)  is  placed  in  the 
cylindrical  chamber  E  F; 
the  steel  cylinder,  which  fits- 
somewhat  loosely  into  the 
chamber,  serves  as  a  pestle. 
The  mortar  is  placed  upon  a  solid  support,  and  perpen- 
dicular blows  are  repeatedly  struck  upon  the  pestle  with  a 
hammer,  until  the  object  in  view  is  attained.  (Fresenius.}- 
In  the  selection  of  agate  mortars,  they  must  be  examined 
to  see  that  they  have  no  palpable  flaws  in  them;  very 
slight  cracks,  however,  that  cannot  be  felt,  do  not  render 
the  mortar  useless,  although  they  increase  the  danger  of 
its  destruction  by  a  chance  blow. 

THE  SIEVE. — The  operation  of  sifting  is  employed  when 
a  very  fine  powder  is  required,  or  when  a  powder  of  uni- 
form size  is  needed.  Sieves  of  various  materials  and 
different  degrees  of  fineness  are  necessary.  The  larger 
sieve,  for  preparing  coke  for  the  blast  furnace,  is  made  of 
stout  iron  wire,  and  must  have  its  meshes  from  1  inch  to 


SIFTING.  17 

IJr  inch  square.  The  fine  coke,  which  is  sifted  from  that 
which  is  the  proper  size  for  the  blast  furnace,  may  be 
mixed  with  that  of  ordinary  size,  and  employed  economi- 
cally in  the  muffle  furnace.  For  the  preparation  of 
minerals  a  set  of  three  sieves  should  be  provided,  each 
one  finer  than  the  other.  The  coarsest  may  contain  40 
holes  to  the  linear  inch,  the  finer  or  medium  sieve  60,  and 
the  finest  from  80  to  100.  The  coarsest  sieve  is  used  for 
preparing  galena  for  assay ;  the  medium  for  copper,  tin, 
iron,  and  other  like  ores ;  and  the  finest  for  gold  and 
silver  ores,  or  for  preparing  any  substance  for  the  wet 
assay,  as,  in  the  latter  case,  the  finer  the  state  of  division 
the  substance  attains,  the  more  rapid  will  be  its  solution 
or  decomposition  by  the  liquid  agents  employed. 

The  sieve  fig.  9  is  made  of  wood,  over  which  is  strained 
in  the  ordinary  manner  brass  wire-gauze  of  the  necessary 
degree  of  fineness.  When  in  use,  B,  fig.  10,  is  fitted  into 
the  lower  part  of  A  (same  figure).  This  contrivance  pre- 
vents all  loss  of  the  fine  powder.  If  the  matter  to  be 
sifted  be  offensive  or  deleterious  to  the  operator,  a  sieve 
termed  the  drum  or  box-sieve  may  be  employed  (see  fig. 
10),  where  C  represents  a  cover  fitting  over  the  sieve.  If 
small,  this  may  be  used  in  the  ordinary  way ;  but  if  large, 
its  method  of  use  is  rather  peculiar,  and  requires  some 
practice  to  fully  develop  its  powers.  One  side  of  the 
under  edge  must  be  FIG>  9.  FIG.  10. 

held  by  one  or  both 
hands  according  to  its 
size,  whilst  the  other 
rests  on  a  table  or  a 
bench.  A  semi-circu- 
lar oscillating  motion 
must  now  be  com- 
municated to  it  by 
moving  the  hands 
up  and  down  at  the 
same  time  that  they 
are  being  alternately  brought  into  approximation  with  the 
sides  of  the  operator. 

c 


18  SIFTING. 

In  cases  of  necessity,  a  sieve  may  be  readily  extem- 
porised. Place  the  powder  to  be  sifted  in  a  piece  of  fine 
lawn  or  muslin,  according  to  the  fineness  required,  tie  it 
up  loosely,  and  shake  or  tap  the  powder,  with  its  muslin 
or  other  envelope,  on  a  sheet  of  paper,  and  the  sifting  will 
be  rapidly  and  easily  accomplished. 

The  sieve  is  also  extremely  serviceable  in  the  separation 
of  some  ores  from  their  gangues  or  vein-stones,  especially 
if  the  latter  be  stony  and  hard.  This  point  must  be  par- 
ticularly noted,  as  it  is  the  cause  of  much  variance  between 
the  results  of  different  assayers ;  for  instance,  part  of  the 
same  sample  of  ore  might  be  sent  to  two  assayers,  and  the 
produce  made  by  one  would  be  8^  per  cent.,  and  that  by 
the  other  9  or  9^,  or,  in  some  cases,  even  more.  This  dis- 
crepancy generally  arises  from  the  cause  above  mentioned. 
In  the  one  case  the  workman  has  rejected  part  of  the 
hard  gangue,  and  so  rendered  the  residue  richer;  whilst 
in  the  other  he  has  pulverised  the  whole,  making  the 
produce  less,  but  giving  more  accurately  the  amount  of 
metal  in  the  substance  submitted  to  assay. 

A  knowledge  of  this  fact  is  also  very  useful  from 
another  point  of  view.  Suppose  it  were  wished  to  separate 
in  a  speedy  manner,  as  perfectly  as  possible,  any  friable 
mineral,  such  as  galena  or  copper  pyrites,  from  its  matrix 
by  mechanical  means,  it  might  be  accomplished  by  the 
use  of  the  sieve,  as  follows :  Place  a  small  quantity  of 
the  mineral  in  an  iron  mortar,  and  strike,  repeatedly, 
slight  vertical  blows.  When  it  is  tolerably  reduced,  sift 
it,  and  it  will  be  found  that  what  passes  through  is  nearly 
pure  mineral,  with  only  a  small  quantity  of  matrix ;  repeat 
the  pounding  and  sifting  operations,  until,  after  a  few 
repetitions,  that  which  remains  in  the  sieve  is  nearly  pure 
gangue. 

Native  metals,  as  gold,  silver,  and  copper,  are  also 
partially  separated  after  the  manner  above  described. 
The  fine  particles  of  metal,  during  the  process  of  pounding 
and  trituration,  become  flattened,  and  cannot  pass  through 
the  sieve,  whilst  the  more  brittle  portions  pass  through 
and  are  separated. 


ELUTRIATION.  19 

ELUTRIATION. — This  process  can  only  be  employed  for 
those  bodies  which  are  not  acted  on  by  water  ;  and  it 
must  be  remembered  that  many  substances  which  are 
usually  considered  to  be  insoluble  in  water  are,  when  in 
a  very  finely  divided  state,  acted  upon  to  a  greater  or  less 
extent.  The  operation  is  thus  effected  :  The  substance  is 
reduced  to  the  finest  possible  state  of  division  by  any  of 
the  foregoing  processes ;  it  is  then  shaken  up  with  a 
quantity  of  water  in  a  glass  or  other  vessel.  After  a  few 
moments'  repose,  the  supernatant  liquid,  retaining  in  sus- 
pension the  finer  particles  of  the  pulverised  substance,  is 
poured  off,  and  the  grosser  parts,  which  have  fallen  to  the 
bottom  of  the  vessel,  are  repulverised,  and  again  treated 
with  water.  By  repeating  these  processes  a  powder  of 
any  required  degree  of  fineness  may  be  obtained. 

It  is  seldom,  however,  that  a  substance  is  required  for 
assay  by  the  dry  way,  in  such  a  minute  state  of  division. 
In  the  humid  or  wet  method  it  is  occasionally  very  useful. 
If  the  supernatant  water  is  roughly  decanted  off,  where 
the  powder  to  be  elutriated  is  light,  the  least  disturbance 
of  the  vessel  containing  it  occasions  the  distribution  of  the 
portion  which  has  settled,  throughout  the  liquid,  and  the 
consequent  mixture  of  fine  and  coarse  particles.  This  can 
be  avoided  by  the  employment  of  the  syphon.  The 
operation  is  then  thus  conducted :  The  syphon  is  filled 
with  water,  and  the  shorter  end  placed  in  the  liquid  whose 
transversion  is  to  be  effected :  the  forefinger  of  the  right 
hand,  which,  during  this  time,  has  been  applied  to  the 
longer  end  of  the  instrument,  is  now  removed,  when  the 
water  will  flow  out  until  it  is  level  with  the  immersed  end 
of  the  syphon.  Fresh  water  can  then  be  added,  the 
powder  stirred  up  again,  and  the  operation  of  decantation 
by  the  syphon  carried  on  as  long  as  requisite. 

WASHING,  DRESSING,  OR  VANNING. — This  operation  is  ex- 
ceedingly useful  for  discovering  the  approximate  quantity 
of  pure  ore,  such  as  galena,  copper  pyrites,  oxide  of  tin, 
native  gold  or  silver,  in  any  sample  of  earthy  matter  or 
ore  in  which  it  may  be  disseminated. 

The  theory  of  the  operation  about  to  be  described  is 

c  2 


20  DRESSING   OR   VANNING. 

easily  understood.  Bodies  left  to  the  action  of  gravity  in  a 
liquid,  in  a  state  of  rest,  experience  a  resistance  to  their 
descent  which  is  proportionate  to  their  surface,  whatever 
may  be  their  volume  and  density.  Hence  it  follows,  firstly, 
that  of  equal  volumes  the  heaviest  fall  most  rapidly ; 
secondly,  that  of  equal  densities  those  having  the  largest 
isize  move  with  the  greatest  speed ;  for  in  particles  of 
unequal  size  and  like  form  the  weight  is  proportional  to 
the  cube  of  the  dimensions,  whilst  the  surface  is  only  pro- 
portional to  the  square  of  these  dimensions  ;  hence  in  small 
particles  the  surface  is  greater  in  relation  to  the  weight 
than  in  the  large  particles.  Thirdly,  of  equal  densities  and 
volumes,  particles  offering  the  largest  surface  (those  which 
are  scaly  and  laminated,  for  example)  undergo  more  re- 
sistance in  their  motion  than  those  which,  approaching 
the  spherical  form,  have  less  surface.  The  adhesion  of 
the  liquid  to  the  particles  of  bodies  held  in  suspension  is 
also  an  obstacle  to  their  subsidence.  This  force,  like  the 
dynamic  resistance,  is  proportional  to  the  surface  and 
independent  of  the  mass  or  volume ;  whence  it  follows 
that,  in  a  fluid  in  motion,  of  bodies  having  equal  volumes, 
the  least  dense  acquire  the  greatest  rapidity  of  movement, 
and  are  deposited  at  the  greatest  distance  from  the  point 
of  departure ;  whilst  with  equal  densities  the  smallest 
grains  are  carried  farthest ;  and  lastly,  with  equal 
densities  and  volumes,  the  particles  exposing  most  surface 
traverse  the  greatest  space. 

It  is,  therefore,  evident  that  the  most  advantageous 
condition  for  separating,  by  washing,  two  substances  of 
unequal  specific  gravity  or  density  is  that  the  heavier 
shall  be  in  larger  grains  than  the  lighter ;  this  unfortun- 
ately, however,  is  a  condition  that  can  very  seldom  be 
fulfilled,  as  the  heaviest  substances  are  those  metallic 
minerals  whose  frangibility  is  nearly  always  greater  than 
the  earthy  matters  accompanying  them  as  gangues.  This 
being  the  case,  it  is  very  important  so  to  arrange  that  the 
fragments  of  the  various  mixed  substances  shall  be  nearly 
of  the  same  size.  This  may  be  effected  by  very  frequently 
sifting  the  mineral  during  the  process  of  pulverisation, 


DRESSING    OR   VANNING.  21 

reducing  it  also  more  by  blows  than  by  grinding,  so  as 
to  get  as  little  fine  powder  as  possible,  as  that  is  nearly 
certain  to  be  washed  away  during  the  process. 

The  operation  of  washing  or  vanning  may  be  performed 
by  one  of  two  methods.  In  the  first,  a  small  stream  of 
running  water  is  employed  ;  in  the  second,  water  is  added 
to  the  substance  to  be  washed,  and  poured  off  as  necessary. 

In  the  first  process,  a  vessel  somewhat  resembling  a 
banker's  gold  scoop  (but  longer  in  proportion)  is  employed ; 
the  mineral  to  be  washed  is  placed  in  the  upper  part,  and  a 
small  quantity  of  water  added,  with  which  the  mineral  is 
thoroughly  and  carefully  moistened,  and  mixed  with  the 
fingers.     The  scoop  must  then  be  so  inclined  that  a  fine 
stream  of  water  from  any  convenient  source  (say  a  tap)  may 
fall  just  above  the  upper  part  of  the  mixture  of  mineral 
and  water ;  then,  firmly  holding  the  larger  and  upper  end 
of  the  scoop  with  the  left  hand,  and  sustaining  the  lower 
part  with  the  right,  it  is  shaken  frequently  in  the  direction 
of  its  longitudinal  axis.     At  each  shake  all  the  particles 
in  the  scoop  are  so  agitated  that  they  become  suspended 
in  the  water,  and  the  current  of  liquid  running  from  the 
tap  into  the  scoop  moves  them  all  in  its  own  direction  ; 
but  they  are  deposited  at  different  distances   from   the 
point  at  which  the  water  enters,  the  heaviest  being  carried 
through  but  a  very  small  space.     It  is  now  soon  seen  that 
the  mineral  assumes  a  heterogeneous  surface  ;  at  the  upper 
part,  the  heavy  portions  are  seen  nearly  pure  ;  the  light 
substances,  on  the  other  hand,  are  nearly  without  mixture 
at  the  lower  end,  and  in  the  intermediate  part  the  heaviest 
portion  of  the  mixture  is  nearest  the  upper  end.     If  the 
washed  matter  were  now  to  be  divided  into  horizontal 
layers,  the  heaviest  matter  would  be  found  at  the  bottom, 
and  the  lightest  on  the  surface.     Things   being   in   this 
state,  the  scoop  must  be  made  to  oscillate  on  its  axis,  so 
that  the  latter  remain  immovable,  and  in  a  slightly  in- 
clined  position.     In   this   manner,   the    layer    of    water 
running  over  the  surface  of  the  mineral  agitates  that  part 
only,  and  carries  off  all  light  substances  there  deposited  in 
the  previous  operation.     When  necessary,  these  matters 


22  DKESSING    OR   VANNING. 

may  be  removed  by  the  finger,  and  made  to  run  into  a 
vessel  placed  below  the  scoop,  in  which  all  the  water  and 
matters  carried  off  are  received.  This  operation,  however, 
must  not  be  hurriedly  performed,  so  as  to  mix  the  parts 
already  separated  :  each  layer  must  be  removed  separately, 
commencing  with  the  upper  one.  This  being  done,  the 
scoop  must  be  alternately  kept  in  motion  by  shakings,  as 
at  first,  and  then  on  its  axis,  and  the  washing  off  of  the 
finer  particles  renewed,  and  so  on  until  the  separation  is 
effected  as  far  as  may  be  judged  necessary. 

At  the  commencement  of  the  operation,  the  water 
carries  out  of  the  scoop  the  lightest  particles,  as  organic 
matter,  clay,  &c. ;  at  a  little  later  period  the  water  carries 
with  it  a  small  but  definite  quantity  of  the  heavier 
portion,  the  proportion  of  which  increases  as  the  operation 
proceeds,  until  at  last  the  greatest  possible  care  is  required. 
It  is  always  better  to  rewash  the  latter  portion  which 
passes  off  from  the  scoop  ;  hence  the  necessity  of  allowing 
all  the  wash-water  passing  from  it  to  collect  in  sc  vessel 
placed  for  that  purpose. 

In  the  second  method  of  washing,  a  tin,  zinc,  or  wooden 
pan  is  employed.  It  should  be  circular,  one  or  two  feet  in 
diameter  and  three  or  four  inches  deep  ;  the  sides  should 
descend  in  a  conical  manner,  so  that  the  bottom  is  not  more 
than  four  inches  in  diameter,  and  the  angle  between  it  and 
the  sides  as  sharp  as  possible. 

The  substance  to  be  examined  is  placed  in  the  washing- 
dish,  the  latter  filled  with  water,  and  the  mineral  well  mixed 
with  it  until  perfectly  moistened  as  before.  After  a  moment 
or  so  the  muddy  water  is  poured  off,  and  the  operation 
repeated  until  the  water  passes  off  clear.  When  this 
happens,  only  so  much  water  must  be  placed  in  the  pan  as 
will  leave  a  slight  layer  on  the  mineral.  Now,  by  holding 
the  pan  in  one  hand,  and  shaking  it  with  the  other,  the 
greater  part  of  the  heavy  mineral,  gold  or  otherwise,  will 
fall  below  the  sand.  If  now  the  pan  be  inclined  towards 
the  hand  which  is  shaking  it,  the  lighter  portions,  even  if 
tolerably  large,  will  flow  off  with  the  water,  leaving  the 
heavier  matters  in  the  angle,  from  which,  with  ordinary 


WEIGHING.  23 

care  and  a  little  practice,  it  is  difficult  to  disturb  them. 
If  there  be  a  large  quantity  of  earthy  matter,  this  may  be 
(after  sufficient  shaking)  removed  by  the  finger,  as  in  the 
first-described  process.  By  careful  repetitions  of  these 
processes,  the  whole,  or  nearly  the  whole,  of  the  sandy 
and  earthy  matters  may  be  removed,  and  the  gold  or 
other  mineral  left  nearly  pure.  This  is  the  plan  employed 
in  prospecting  for  gold,  diamonds,  and  other  gems,  and  in 
some  cases  for  their  commercial  extraction. 

In  Cornwall  and  other  mining  counties  this  operation 
is  very  cleverly  and  carefully  performed  on  the  miner's 
common  shovel,  and  the  richness  of  any  particular  sample 
of  either  tin,  lead,  or  copper  is  thereby  determined  with  a 
very  near  approach  to  accuracy. 

THE  BALANCE. 

OPERATION  OF  WEIGHING. — At  least  three  balances  will 
be  required  in  a  laboratory  where  general  assays  are  per- 

FlG.    11. 


formed.     The  first  must  be  capable  of  carrying  three  or 


24  '  WEIGHING. 

four  pounds  in  each  pan,  and  must  turn  with  a  quarter  of 
a  grain.     This  may  be  of  the  form  of  the  bankers'  or 

FIG.  12. 


bullion  balance  (fig.  11),  and  may  be  employed  in  weigh- 
ing samples  of  gold  quartz  or  silver  ore  containing  metallic 


FIG.  13. 


THE   BALANCE.  25 

grains  capable  of  being  separated  by  the  sieve  (see  p.  18) ; 
the  second  (fig.  12),  or  rough  assay  balance,  is  similar  to 
the  apothecary's  scales  ;  it  should  take  1,000  grains  in 
each  pan,  and  turn  with  one  tenth  of  a  grain.  This  serves 
for  weighing  samples  of  ore  and  fluxes  for  assay,  and  for 
determining  the  weight  of  buttons  or  prills  of  lead,  tin, 
iron,  copper,  &c.,  obtained  in  an  assay. 

The  third  and  most  delicate,  or  true,  assay  balance  (fig. 
13)  should  carry  about  1,000  grains  ;  must  turn  distinctly 
and  accurately  with  the  ToVo^1  °^  a  grain.  This  is 
employed  in  the  assay  of  gold  and  silver  bulhon,  and  in 
the  assay  of  minerals  containing  gold  and  silver  ;  also  for 
general  analytical  purposes.  The  first  two  balances  may 
be  used,  with  ordinary  care,  by  any  one  ;  but  the  third 
balance,  in  its  use  and  adjustment  so  as  to  maintain  its 
extreme  accuracy,  requires  some  particular  instructions, 
which  necessarily  involve  the  principle  of  the  balance. 
These  have  been  so  admirably  given  by  Faraday,  in  his 
'  Chemical  Manipulations,'  that  we  can  do  no  better  than 
transcribe  them  : — 

4  The  theory  of  this  balance  is  so  simple  that  the  tests 
of  its  accuracy  will  be  easily  understood  and  as  easily 
practised.  It  may  be  considered  as  a  uniform  inflexible 
lever,  supported  horizontally  at  the  centre  of  gravity,  and 
supporting  weights  at  equal  distances  from  the  centre  by 
points  in  the  same  horizontal  line  with  the  centre  of 
gravity.  If  the  weights  be  equal  the  one  will  counter- 
poise the  other  ;  if  not,  the  heavier  will  preponderate. 
In  the  balance,  as  usually  constructed,  there  are  certain 
departures  from  the  theory  as  above  expressed — some 
from  the  impossibility  of  execution,  and  others  in  conse- 
quence of  their  practical  utility  ;  and  a  good  balance  may 
be  said  to  consist  essentially  of  a  beam  made  as  light  as  is 
consistent  with  that  inflexibility  which  it  ought  to  possess, 
divided  into  two  arms  of  equal  weight  and  length  by  a 
line  of  support  or  axis,  and  also  terminated  at  the  end  of 
each  arm  by  a  line  of  support  or  axis,  intended  to  sustain 
the  pans.  These  three  lines  of  support  should  be  exactly 
parallel  to  each  other  in  the  same  horizontal  plane,  and 


26  WEIGHING. 

correctly  perpendicular  to  the  length  of  the  beam ;  and 
the  plane  in  which  they  lie  should  be  raised  more  or  less 
above  the  centre  of  gravity  of  the  beam,  so  that  the  latter 
should  be  exactly  under  the  middle  line  of  suspension. 
It  will  be  unnecessary  in  this  place  to  speak  of  the  coarse 
faults  which  occur  in  the  ordinary  scales — these  will  be 
easily  understood  ;  and  from  what  has  to  be  stated  of  the 
examination  of  the  most  delicate  instrument,  the  impos- 
sibility of  avoiding  them  without  incurring  an  expense 
inconsistent  with  their  ordinary  use  will  be  as  readily 
comprehended.' 

Two  principal  things  have  to  be  attended  to  in  the 
selection  of  a  balance — its  accuracy  and  its  delicacy.  The 
accuracy  depends  upon  the  following,  conditions  : — 

1.  The  arms  should  be  equal  to  each  other  in  length.  The 
length  of  each  is  accurately  the  distance  from  the  middle 
to  the  distant  knife-edge,  all  the  edges  being  considered 
parallel  to  each  other,  and  in  the  same  plane.  The  two 
arms  should  accord  perfectly  in  this  respect.  This  equality 
may  be  ascertained  in  two  or  three  ways.  Suppose  the 
balance  with  its  pans  to  vibrate  freely,  and  rest  in  a 
horizontal  position,  and  that  after  changing  the  pans  from 
one  end  to  the  other  the  balance  again  takes  its  horizontal 
state  of  rest — in  such  a  case  an  almost  certain  proof  is 
obtained  of  equality  in  length  of  the  arms.  They  may, 
however,  be  equal,  and  yet  this  change  of  the  pans  from 
end  to  end  may  occasion  a  disturbance  of  equilibrium, 
because  of  the  unequal  distribution  of  weight  on  the  beam 
and  pans  ;  but  to  insure  an  accurate  test,  restore  the  pans, 
and  consequently  the  equilibrium,  to  the  first  state :  put 
equal,  or  at  least  counterpoising,  weights  into  the  pans, 
loading  the  balance  moderately,  and  then  change  the 
weights  from  one  pan  to  the  other,  and  again  observe 
whether  the  equilibrium  is  maintained  ;  if  so,  the  length 
of  the  arms  in  equal. 

Equality  of  weight  is  not  so  necessary  a  condition, 
although  this  should  be  obtained  as  accurately  as  possible. 
One  arm  with  its  pan  may  be  considerably  heavier  than 
the  other,  but  from  the  disposition  of  the  weight  in  the 


THE   BALANCE.  27 

lighter  arm  towards  the  extremity,  or  in  the  heavier 
towards  the  middle  of  the  beam,  the  equilibrium  may  be 
perfect,  and  therefore  no  inaccuracy  be  caused  thereby  in 
the  use  of  the  balance.  Instruments  are  usually  sent  home 
in  equilibrium,  and  require  no  further  examination  as  to 
this  particular  point  than  to  ascertain  that  they  really  are 
in  adjustment,  and  that  after  vibrating  freely  they  take  a 
horizontal  position. 

2.  The  beam  must  be  of  such  a  form  and  strength  that 
it  will  not  bend  when  loaded  with  the  greatest  weight  the 
balance   is    intended    to    carry.      All  well-made   modern 
balances  are  sufficiently  rigid  in  this  respect,  and  may  be 
safely  trusted  to  carry  their  full  weight  without  flexure  of 
the  beam.     It  should  also  be  as  light  as  practicable. 

3.  The  knife-edges  supporting  the  pans,  and  the  centre 
one  on  which  the  beam  vibrates,  must  be  accurately  in  the 
same  line. 

The  delicacy  of  a  balance  likewise  depends  upon 
several  conditions. 

The  centre  of  gravity  must  be  very  little  below  the 
Jidcrum.  If  it  be  considerably  depressed,  then,  upon 
trying  the  oscillations  of  the  balance  by  giving  it  a  little 
motion,  they  will  be  found  to  be  quick,  and  the  beam 
will  soon  take  its  ultimate  state  of  rest ;  and  if  weights  be 
added  to  one  side,  so  as  to  make  it  vibrate,  or  to  bring  it 
to  a  certain  permanent  state  of  inclination,  the  quantity 
required  will  be  found  to  be  comparatively  considerable. 
As  the  centre  of  gravity  is  raised  the  oscillations  are 
slower,  but  producible  by  a  much  smaller  impulse ;  the 
beam  is  a  longer  time  before  it  attains  a  state  of  rest,  and 
it  turns  with  a  smaller  quantity. 

If,  however,  the  centre  of  gravity  coincides  with  the 
fulcrum  or  centre  of  oscillation,  then  the  balance  is  said 
to  set,  that  is,  the  smallest  possible  weight  will  turn  the 
beam  ;  the  oscillations  no  longer  exist,  but  one  side  or 
the  other  preponderates  with  the  slightest  force,  and  the 
valuable  indication  which  is  furnished  by  the  extent  and 
velocity  of  the  vibrations  is  lost. 

The  case  in  which  the  centre  of  gravity  is  above  the 


28  .  WEIGHING. 

fulcrum  rarely  if  ever  occurs.  Such  a  balance,  when 
equally  weighted,  would  set  on  the  one  side  or  the  other ; 
that  side  which  was  in  the  slightest  degree  lower  tending 
to  descend  still  further,  until  obstructed  by  interposing 
obstacles. 

In  balances  intended  to  carry  large  quantities  (as  in 
the  balance  for  weighing  gold  quartz,  &c.)  it  is  necessary 
to  place  the  centre  of  gravity  lower  than  in  those  for 
minute  quantities,  that  they  may  vibrate  regularly  and 
readily.  This  is  one  cause  why  they  are  inferior  in  deli- 
cacy, for,  as  a  consequence  of  the  arrangement,  they  will 
not  turn  except  with  a  larger  weight. 

Balances  are  also  liable  to  set  when  overloaded.  Thus, 
if  a  balance  be  equally  weighted  in  each  pan,  but  over- 
loaded, it  will,  if  placed  exactly  horizontal,  remain  so,  but 
the  slightest  impulse  or  depression  on  one  side  destroys 
the  equilibrium  ;  the  lower  side  continues  to  descend  with 
an  accelerated  force,  and  ultimately  remains  down,  being 
to  all  appearance  heavier  than  the  other.  Generally 
speaking,  the  more  delicate  a  balance  the  sooner  this- 
effect  takes  place ;  this  is  one  limit  to  the  weight  it  can 
properly  carry. 

The  vibrations  of  a  balance  vary  with  the  quantity  of 
matter  with  which  it  is  loaded :  the  more  the  weight  in 
the  pans,  the  slower  the  vibrations.  These  should  be 
observed,  and  the  appearances  retained  in  the  mind,  in 
consequence  of  the  useful  indications  they  afford  in 
weighing.  A  certain  amplitude  and  velocity  of  vibration 
would  indicate  to  a  person  used  to  the  instrument  nearly 
the  weight  required  to  produce  equilibrium  ;  but  the  same 
extent  and  velocity,  with  a  weight  much  larger  or  smaller, 
would  not  be  occasioned  by  an  equal  deficiency  or  redund- 
ancy of  weight,  as  in  the  former  case. 

The  weight  also  required  to  effect  a  certain  inclination 
of  the  beam,  or  to  turn  it,  should  be  known,  both  when  it 
is  slightly  and  when  it  is  heavily  loaded.  Thus,  if  the 
instrument  turns  with  10100th  of  a  grain,  with  1,000  grains 
in  each  pan,  or  with  Ioo^000th  of  the  weight  it  carries,  it 
may  be  considered  perfect. 


THE   BALANCE.  29 

The  friction  of  the  knife-edges  must  be  as  slight  as 
possible. 

Most  of  the  faults  in  the  working  of  a  balance,  if  ordin- 
arily well  made,  depend  upon  imperfections  in  the  middle 
knife-edge  and  the  planes  upon  which  it  rests. 

The  edge  is  made  either  of  agate  or  steel,  preferably 
the  former,  and  should  be  formed  out  of  one  piece,  and 
finished  at  once,  every  part  of  the  edge  being  ground  on 
the  same  flat  surface  at  the  same  time.  In  this  way  the 
existence  of  the  two  extreme  or  bearing  parts  of  the  edge 
in  one  line  is  insured  ;  but  when  the  two  parts  which  bear 
upon  the  planes  are  formed  separately  on  the  different 
•ends  of  a  piece  of  agate  or  steel,  or,  what  is  worse,  when 
they  are  formed  on  separate  pieces,  and  then  fixed  one  on 
each  side  the  beam,  it  is  scarcely  possible  they  should  be 
in  the  same  line  :  and  if  not,  the  beam  cannot  be  correct. 
These  knife-edges  usually  rest  on  planes,  or  else  in  curves. 
The  planes  should  be  perfectly  flat  and  horizontal,  and 
exactly  at  the  same  height ;  the  curves  should  be  of  equal 
height,  and  their  axes  in  the  same  line.  If  they  are  so, 
and  the  knife-edge  is  perfect,  then  the  suspension  will  be 
accurately  on  the  line  of  the  edge,  and  reversing  the  beam 
will  produce  no  change.  The  balance  must  always  be 
kept  perfectly  level  by  means  of  the  three  screws  on 
which  it  stands,  and  adjusted  by  the  spirit-level  or  plumb- 
line  with  which  it  is  furnished. 

The  balance  should  be  kept  in  a  well-lighted  dry  room, 
quite  away  from  acid  or  other  vapours.  The  case  should 
be  kept  closed  as  much  as  possible,  and  a  glass  vessel  full 
of  lumps  of  good  quick-lime  should  be  kept  in  it.  When 
the  lime  falls  to  powder  it  should  be  renewed. 

In  order  to  test  the  accuracy  and  delicacy  of  a  balance, 
remove  the  pans  and  their  end  supports,  and  notice  how 
the  beam  oscillates:  When  it  has  been  found  to  oscillate 
with  regularity,  and  gradually  to  attain  a  horizontal  posi- 
tion of  rest,  it  should  be  reversed — that  is,  taken  up  and 
turned  half-way  round,  so  as  to  make  that  which  before 
pointed  to  the  right  now  point  to  the  left.  The  beam 
should  then  again  be  made  to  oscillate,  and  if  it  perform 


30  WEIGHING. 

regularly  as  before,  finally  resting  in  a  horizontal  position,, 
it  has  stood  a  severe  test,  and  promises  well.  Then  re- 
place the  pans  and  repeat  the  tests,  noticing  the  time 
required  for  each  oscillation.  When  the  pans  are  hung 
upon  the  beam,  the  balance  should  of  course  remain 
horizontal.  They  should  be  tried  by  changing,  then  by 
reversing,  the  beam,  and  afterwards  by  changing  the  pans- 
again.  The  pans  are  best  suspended  by  very  thin  platinum 
wire,  so  as  to  avoid  hygrometrical  influence  upon  them. 

Afterwards  load  the  balance  with  the  full  weight  it 
is  intended  to  carry — say  1,000  grains  in  each  pan,  and 
notice  if  the  indications  are  as  rapid  upon  adding  or  sub- 
tracting the  smallest  weight  as  they  were  when  the  pans 
were  empty. 

Tests  of  this  kind  are  quite  sufficient  for  the  purpose 
of  the  assayer,  who,  having  ascertained  that  his  balance, 
whether  slightly  or  fully  laden,  vibrates  freely,  turns  deli- 
cately, has  not  its  indications  altered  by  reversing  the 
beam  or  changing  counterpoising  weights,  may  be  perfectly 
satisfied  with  it. 

The  irregularities  which  may  be  discovered  by  these 
tests  are  best  corrected  by  a  workman  ;  but  as  in  all  the 
best  balances  now  made  adjusting  screws  for  these  pur- 
poses are  provided,  it  has  been  thought  advisable  to 
introduce  here  such  matter  as,  after  careful  perusal,  will 
enable  every  one  to  adjust  and  examine  his  balance 
properly ;  so  that,  in  the  absence  of  a  skilled  workman, 
it  may  without  much  danger  be  put  into  working  order 
by  the  assayer  himself,  if  accidentally  damaged  by  rough 
treatment. 

THE  WEIGHTS. — Various  kinds  of  weights  are  necessary 
for  the  different  balances  required  by  the  assayer.  For 
the  larger  balance,  Troy-weights  from  4  Ibs.  to  i  grain 
will  be  requisite  ;  for  the  second  size,"  weights  from  1,000 
grains  to  -p^th  part  of  a  grain  ;  and  for  the  assay  balance,, 
weights  from  1,000  grains  to  yoVoth  of  a  grain. 

The  best  material  adapted  for  weights  is  unquestion- 
ably platinum.  This  is,  however,  too  expensive  for  its 
general  adoption,  and  therefore  brass  weights  are  almost 


THE    WEIGHTS  31 

invariably  employed  down  to  the  ten-  or  twenty-grain 
weight,  the  smaller  ones  only  being  of  platinum.  On  the 
Continent  weights  are  generally  made  of  silver,  and  if  of 
brass  are  electro-gilt.  For  the  smallest  weights  of  all 
(those  below  (HO  grain)  aluminium  is  often  used,  its 
lightness,  and  consequently  greater  bulk,  enabling  these 
small  weights  to  be  made  considerably  larger  than  if  they 
were  of  platinum.  The  riders  are  generally  of  silver-gilt 
wire.  The  slight  tarnish  which  gradually  forms  on  brass 
weights  may  be  disregarded  until  it  becomes  thick. 
Weights  ought  never  to  be  touched  with  the  fingers,  and 
should,  when  not  in  use,  be  kept  tightly  fastened  in  their 
box,  away  from  all  acid  fumes.  The  most  convenient 
series  in  which  to  have  the  weights  is  600,  300,  200,  100, 
60,  30,  20,  10,  6,  3,  2,  1,  -6,  -3,  -2,  -1,  &c.  This  is  pre- 
ferable to  the  series  formerly  employed,  as  it  admits  of  the 
use  of  a  less  number  of  weights  to  arrive  at  any  required 
amount. 

According  to  H.  Ste.  Claire  Deville  and  Mascart  re- 
ceptacles lined  with  velvet  are  not  adapted  for  the  preser- 
vation of  weights,  as  dust  is  deposited  in  the  velvet  and 
acts  upon  the  weights  when  taken  out  or  put  in.  Small 
boxes  of  ivory  or  smooth  wood  are  preferable. 

Peculiar  weights  are  necessary  for  the  assay  of  gold 
and  silver  bullion  in  England  (with  the  exception  of  assays 
for  the  Bank  of  England ;  see  Gold  assay),  gold  being  re- 
ported in  carats,  grains,  and  eighths,  and  silver  in  ozs.  and 
dwts.  The  most  convenient  quantity  of  either  of  the 
precious  metals  for  assay  is  12  grains.  The  quantity 
taken,  however,  is  of  no  very  great  consequence  ;  but 
whatever  its  real  weight,  it  is  denominated  in  England 
the  assay  'pound.'  This  assay  '  pound '  is  then  subdivided 
into  aliquot  parts,  but  differing  according  to  the  metal. 
The  silver  assay  '  pound '  is  subdivided,  as  the  real  Troy 
pound,  into  12  ounces,  each  ounce  into  20  pennyweights, 
and  these  again  into  halves  (the  lowest  report  for  silver), 
so  that  there  are  480  different  reports  for  silver,  and 
therefore  each  nominal  half-pennyweight  weighs  ^th  part 
of  a  Troy  grain,  when  the  '  pound  '  is  twelve  grains. 


32 


WEIGHING. 


Silver 
ozs.  dwts.  grs. 

12  0  0 
11  0  0 
600 
300 
200 
100 
0  10  0 
050 
030 
020 
0  1 


Assay  Weights  for  Silver. 


0 


0    0  12 


Assay 
grains. 

12 

11 
6 
3 
2 
1 

0-500 
0-250 
0-150 
0-100 
0-050 
0-025 


The  gold  assay  '  pound '  is  subdivided  into  24  carats, 
each  carat  into  4  assay  grains,  and  each  grain  into  eighths, 
so  that  there  are  768  reports  for  gold  ;  and  the  assay 
'  pound  '  weighing  12  Troy  grains,  the  lowest  report,  or  -J-th 
assay  grain,  equals  ^¥th  Troy  grain  ;  thus — 

Assay  Weights  for  Gold. 


Gold 

carats,  grs.  eighths. 

24    0    0 

22 

0 

0 

12 

0 

0 

6 

0 

0 

3 

0 

0 

2 

0 

0 

1 

0 

0 

0 

2 

0 

0 

1 

0 

0 

0 

6 

0 

0 

3 

0 

0 

2 

0 

0 

1 

grains. 

12 

11 

6 


Iffths 
1 
fltlis 


In  cases  where  the  very  smallest  weights  have  to  be 
employed,  great  care  must  be  taken  in  seizing  them  with 
the  forceps,  as  they  are  apt  to  spring  away  and  be  lost. 
In  the  assay  balance  (fig.  13)  the  use  of  weights  less  than 
T\j-th  of  a  grain  is  avoided  by  a  very  ingenious  contrivance. 
Each  side  of  the  beam  is  equally  divided  into  ten  parts, 
and  over  the  beam  on  each  side  is  placed  a  sliding  rod, 
as  represented  in  the  figure.  The  object  of  these  rods  is 
to  carry,  in  the  direction  of  the  beam,  the  small  bent  piece 
of  wire  (letter  c,  fig.  13)  called  a  rider 9  which  serves  in 


WEIGHING  33 


lieu  of  the  smallest  weights  —  the  yj^th  and  the  10100th. 
These  riders  are  thus  employed  :  one  weighing  -^-g-th  of  a 
grain  is  placed  on  the  cross-piece  of  the  extremity  of  the 
sliding  rod  just  mentioned,  and  the  rod  thus  furnished  is 
brought  gradually  along  the  beam  from  the  centre  to  the 
end,  until  the  rider  can  be  deposited  on  the  division  on 
the  beam  marked  10  ;  the  balance  is  then  loaded  on  that 
side  with  a  weight  equal  to  -^th  of  a  grain.  If  now  the 
rod  be  advanced  to  the  centre  of  the  balance,  and  the  rider 
dropped  on  the  mark  5,  the  half  of  -p^th  of  a  grain  will  be 
pressing  on  that  side  of  the  balance,  or,  in  other  words, 
•05th  of  a  grain  ;  and  when  the  rider  is  at  the  marks  1,  2, 
3,  4,  respectively,  -01,  *02,  -03,  -04  of  a  grain  will  be  in- 
dicated. With  a  rider  weighing  y^th  of  a  grain  thou- 
sandths of  grains  may  be  indicated  :  thus  the  last  rider 
placed  on  the  marks  1,  2,  3,  4  would  equal  -001,  -002, 
•003,  -004  grain,  &c. 

THE  METHOD  OP  WEIGHING.  —  The  operation  of  weighing  is 
very  simple  ;  but  as  in  the  hands  of  the  assayer  it  becomes 
one  of  great  frequency,  the  facilities  for  its  performance 
require  to  be  mentioned.  It  should  in  the  first  place  be  as- 
certained before  every  operation  that  the  balance  is  in  order, 
so  far  as  relates  to  its  freedom  of  vibration,  and  also  that 
no  currents  of  air  are  passing  through  the  case,  so  as  to 
affect  its  state  of  motion  or  rest,  a  situation  being  chosen 
where  such  influence  may  be  avoided.  In  most  cases  there 
is  a  small  projecting  arm  on  the  upper  part  of  the  beam, 
which,  being  turned  either  to  the  right  or  left  hand  side 
of  the  beam  as  required,  serves  to  establish  perfect  equili- 
brium. Perfect  equilibrium  is,  however,  a  matter  of  no 
consequence  if  the  assayer  observes  one  or  two  simple 
rules.  He  should  never  on  any  account  weigh  by  the  direct 
method,  that  is,  he  should  never  obtain  the  weight  of  a 
substance  by  putting  it  at  once  into  one  pan  and  then 
counterpoising  it  by  adding  weights  to  the  other  pan. 
This  method  is  only  to  be  relied  on  when  the  balance  is  of 
rare  perfection,  and  is  used  by  no  one  but  the  assayer  him- 
self. The  plan  of  weighing  by  difference  should  invariably 
be  adopted.  By  this  means  the  weight  of  any  body  can 

D 


84  WEIGHING. 

be  readily  ascertained,  no  matter  whether  the  arms  of  the 
balance  are  of  unequal  length  or  the  pans  out  of  equilibrium. 

In  the  first  place,  it  should  be  a  rule  that  one  panr 
preferably  the  left,  be  reserved  for  the  substance  to  be 
weighed,  and  the  other  pan  be  set  apart  for  the  weights. 

Supposing  the  weight  of  a  portion  of  mineral  is  re- 
quired. First  place  a  clean  watch-glass,  or  platinum 
capsule,  in  the  left  pan,  and  carefully  ascertain  its  weight. 
Let  us  suppose  it  weighs  106-347  grains ;  now  put  the 
mineral  in  the  watch-glass  and  ascertain  the  united  weight 
of  the  two.  This  we  will  imagine  comes  to  763-776.  By 
subtracting  the  weight  of  the  glass  or  capsule  from  this 
we  find  the  true  weight  of  the  mineral,  which  is  763-776 
-106-347  =  657-429.  The  substance  to  be  weighed  must 
n ever  be  put  direct  into  the  pan.  By  weighing  in  this 
manner  by  difference,  the  errors  arising  from  inequality  in 
the  equilibrium  or  length  of  arms  are  eliminated. 

Nothing  should  ever  be  weighed  until  it  is  perfectly 
cold.  It  is  also  unadvisable  to  weigh  anything  immediately 
after  it  is  taken  from  a  cold  place  to  a  warmer  one,  as  the 
substance  in  such  case  will  act  as  a  hygroscopic  body, 
and,  by  condensing  moisture,  will  appear  heavier  than  it 
really  is. 

Powders  are  conveniently  weighed  by  filling  a  small 
stoppered  tube  bottle  with  them,  then  weighing  the  whole, 
and,  after  pouring  out  the  requisite  amount  of  its  contents, 
re  weighing  the  bottle  and  powder.  The  difference  gives 
the  weight  of  powder  used.  This  is  a  very  convenient 
plan  if  several  portions  of  the  same  substance  are  required 
for  different  analyses.  The  tube  will  require  reweighing 
each  time  after  the  quantities  required  for  each  analysis 
are  shaken  out  into  the  receptacles. 

A  delicate  balance  is  always  furnished  with  means  of 
supporting  the  pans  independent  of  the  beam ;  and  the 
beam  itself  is  also  supported  when  required  by  other  bear- 
ings than  its  knife-edges,  and  in  such  a  manner  as  to  admit 
of  the  rapid  removal  of  these  extra  supports  when  the 
instrument  is  to  be  free  for  vibration.  This  is  done  that 
the  delicate  edges  of  suspension  may  not  be  injured  by 


WEIGHING.  8# 

being  constantly  subjected  to  the  weight  of  the  beam  and 
the  pans,  and  that  they  may  suffer  no  sudden  injury  from 
undue  violence  or  force  impressed  upon  any  part  of  the 
balance.  When,  therefore,  a  large  weight  of  any  kind  is 
put  into  or  removed  from  the  pans,  it  should  never  be 
done  without  previously  supporting  them  by  these  contriv- 
ances;  for  the  weight,  if  dropped  in,  descends  with  a 
force  highly  injurious  to  the  supporting  edges  ;  also,  if  a 
large  weight  be  taken  out  without  first  bringing  the  pans 
to  rest,  it  produces  a  similarly  bad  effect. 

The  weights  should  not  be  put  into  the  pan  at  random. 
It  is  a  mistake  to  suppose  that  time  is  saved  by  such  a 
plan.  The  highest  probable  weight  should  be  added  first, 
and  then  the  set  should  be  gone  through  systematically 
down  to  the  smallest  weight,  retaining  or  removing  each 
weight  in  order  according  as  it  is  too  little  or  too  muchi 
The  exact  weight  of  a  body  will  be  found  in  this  manner 
in  far  less  time  than  would  be  required  were  the  weights 
added  by  guess. 

When  a  weight  is  put  in  which  is  assumed  to  be  nearly 
equal  to.  the  substance  to  be  weighed,  the  balance  should 
be  brought  to  a  state  of  rest,  and  should  then  be  liberated 
gradually  by  turning  the  handle,  so  as  to  leave  the  pans 
wholly  supported  by  the  beam.  The  whole  being  on  its 
true  centres  of  suspension,  it  will  be  observed  whether  the 
weight  is  sufficient  or  not ;  and  the  rapidity  of  ascent  or 
descent  of  the  pan  containing  it  will  enable  a  judgment  to 
be  formed  of  the  quantity  still  to  be  added  or  removed. 

Great  care  should  be  observed  in  recording  the  weight 
in  the  notebook.  The  weight  should  first  be  ascertained 
from  an  inspection  of  the  vacancies  in  the  box  of  weights, 
and  then  verified  by  an  examination  of  the  weights  them- 
selves. This  is  conveniently  done  whilst  replacing  them 
in  the  box,  which  should  be  done  immediately  after  each 
weighing. 

In  some  cases,  where  great  accuracy  is  not  of  so  much 
importance  as  rapidity  in  getting  out  approximate  results,. 
a  plan  may  be  adopted  recommended  by  Mr.  F.  F.  Mayer- 
an  the  American  '  Journal  of  Science  and  Art  '.for  186-1. 

D    2 


36  WEIGHING   MOIST   PRECIPITATES. 

Mr.  Ch.  Mene,  of  Creusot,  gave  (in  the  '  Journ.  de 
Pharm.  et  de  Chimie '  for  October  1858)  a  mode  of  weigh- 
ing which  does  away  to  a  great  extent  with  the  tedious- 
ness  and  difficulties  attending  the  dryness  of  many  pre- 
cipitates. He  washes  the  precipitate  thoroughly  by 
decantation,  and  then  introduces  it  carefully  into  a  bottle 
the  exact  weight  of  which  when  filled  with  distilled  water 
at  a  certain  temperature  is  known.  Since  the  precipitate 
is  heavier  than  water,  the  bottle,  when  filled  again,  will 
weigh  more  than  without  the  precipitate,  and  the  differ- 
ence between  the  two  weights  furnishes  the  means  of  cal- 
culating the  weight  of  the  precipitate. 

In  case  the  precipitate  settles  but  slowly,  it  may  be 
collected  on  a  filter,  and,  together  with  a  filter,  after  wash- 
ing, be  introduced  into  the  bottle,  in  which  case  the  weight 
of  the  filter  and  its  specific  gravity,  supposing  any  differ- 
ence should  exist  between  its  own  and  that  of  water,  is  to 
be  taken  into  account.  Precipitates  soluble  in  or  affected 
by  water  may  be  weighed  in  some  other  liquid. 

Mr.  Mayer  applied  this  principle  on  a  large  scale  as  far 
back  as  1855. 

In  that  year  he  was  engaged  in  the  manufacture  of 
lead  carbonate  from  refuse  lead  sulphate,  by  treating  the 
latter,  in  a  pulpy  condition,  with  sodium  carbonate.  The 
lead  sulphate  used  contained  very  varying  proportions  of 
water  and  soluble  impurities,  from  which  latter  it  had 
first  to  be  freed  by  washing.  It  was  then  in  the  state  of  a 
thin  pulp,  and  the  difficulty  was  to  find  the  amount  of  the 
dry  lead  sulphate,  as  it  was  a  matter  of  importance  to  use 
as  little  sodium  carbonate,  and  to  obtain  as  pure  a  lead  car- 
bonate and  sodium  sulphate,  as  possible.  This  could  only 
be  done  by  weighing  it  in  the  bulk  or  in  portions ;  but  as 
the  drying  of  a  tubful  of  lead  sulphate  (from  500  to  1,200 
Ibs,)  was  impracticable,  and  sampling  not  less  so,  since 
the  upper  strata  contained  a  much  larger  proportion  of 
water  than  the  lead  at  the  bottom,  the  following  method 
was  contrived,  wrhich  enabled  the  management  of  the  pro- 
cess to  be  left  in  the  hands  of  a  workman  : — 

A  strong  oaken  pail  was  taken,  weighing  8  Ibs.  when 


WEIGHING   MOIST   PRECIPITATES.  37 

empty,  and  a  black  mark  was  burnt  in  horizontally  around 
the  inside  of  the  pail  two  inches  below  the  rim,  up  to 
which  mark  it  held  20  Ibs.  of  water.  The  specific  gravity 
of  lead  sulphate  being  6*3,  the  pail,  if  filled  up  to  the 
mark,  would  hold  126  Ibs.  of  pure  lead  sulphate.  The 
specific  gravity  of  water  being  5*3  less  than  that  of  lead 
sulphate,  it  followed  that  if  there  were  1  Ib.  of  water  in  the 
pailful  of  moist  sulphate,  the  pail  would  weigh  5-3  Ibs/ less 
than  126  (  +  8,  the  tare  of  the  pail)  =  120-7 (  +  8) ;  -if  there 
were  2  Ibs.  of  water  present,  the  weight  would  be  1 115-4 
(-f-8),  and  so  on.  This  enabled  a  table  to  be  calculated 
giving  in  one  column  the  actual  weight  of  the  pailwhen 
filled  with  moist  sulphate,  and  opposite,  in  a  second  column, 
the  amount  of  dry  sulphate  corresponding  to  the  gross 
weight.  The  weight  of  dry  sulphate  was  thus  found, as: 
accurately  as  could  be  desired,  although  the  amounts 
varied  in  practice  from  30  to  105  Ibs. 

This  is  nothing  but  an  application  of  the  Archimedean 
theorem,  that  when  a  solid  body  is  immersed  in  a  liquid 
it  loses  a  portion  of  its  weight  equal  to  the  weight  of  the 
fluid  which  it  displaces,  or  to  the  weight  of  its  own  bulk  of 
the  liquid. 

This  is  precisely  the  principle  applied  by  Mr.  Mene. 
The  precipitate  he  obtains  by  a  certain  chemical  manipu- 
lation is  a  substance  of  known  composition  and  specific 
gravity.  Supposing  it  to  be  lead  sulphate,  and  the  bottle 
when  filled  with  water  at  the  normal  temperature  to  weigh- 
70  grammes  =  50  grammes  of  water  and  20  for  tare.  After 
introducing  the  precipitate  and  filling  again  with  water,  it 
weighs  71*06  grammes.  Now  as  the  specific  gravity  of 
lead  sulphate  is  6 -3,  or  as  the  weight  of  a  cubic  measure 
of  lead  sulphate  is  6  -3  times  that  of  a  cubic  measure  of 
water,  and  as  the  space  of  one  part  by  weight  of  water,  is 
taken  up  by  6'2  parts  by  weight  of  lead  sulphate,  it  follows 
that  the  quantity  of  the  lead  sulphate  in  the  bottle,  which 
has  taken  up  the  space  of  one  part  by  weight  of  water,  inv 
creases  the  original  weight  of  the  bottle  (filled  with  pure 
water)  by  5*3.  To  find  the  amount  of  water  displaced  it 
is  only  necessary  to  divide  the  overweight  (1 '06  grammes) 


38  WEIGHING   MOIST   PRECIPITATES. 

by  5-3-0-2,  which,  added  to  the  overweight  (1-06  +  0-2), 
gives  1*26  grammes  as  the  weight  of  the  precipitate. 

Hence  the  rule,  which  is  of  great  convenience  in 
volumetric  analysis,  that  to  find  the  weight  of  a  moist 
precipitate  which  is  a  compound  of  known  specific  gravity, 
weigh  it  in  a  specific  gravity  bottle  or  some  other  vessel 
of  known  weight  when  filled  with  water  or  any  other 
liquid  at  the  normal  temperature ;  again  fill  it  with  the 
water  or  other  liquid,  divide  the  excess  of  the  new  weight 
by  the  specific  gravity  of  the  substance,  less  that  of  the 
water  or  other  liquid  (that  of  water  being  =1),  and  add 
the  quotient  to  the  overweight,  which  gives  the  weight  of 
the  precipitate. 

The  principle  exemplified  by  Mr.  Mayer  may  not  be 
novel ;  but  as  it  has  never  been  fully  exemplified  before, 
chemists  and  assayers  will  probably  also  find  it  of  interest, 
and  certainly  highly  practicable  and  easy  of  execution. 

Dr.  F.  Muck  ('  Zeitschrift  fur  Analytische  Chemie,'  vol. 
xix.  p.  131)  remarks  that  a  previous  complete  drying  of 
the  precipitate,  as  Bunsen  has  proved,  is  not  merely  a  loss 
of  time  but  a  disadvantage  ;  whilst  introducing  the  still 
moist  precipitate  into  the  crucible  requires  the  application 
of  a  very  gentle  heat  at  the  outset,  and  thus  insures  the 
most  favourable  conditions  ipr  the  easy  and  complete 
incineration  of  the  filter-paper.  Precipitates  not  washed 
upon  the  filter-pump  can  be  readily  brought  to  a  sufficient 
degree  of  dryness  if  laid  for  a  short  time  upon  blotting- 
paper  or  unglazed  earthenware. 

Dry  filters  may  be  also  much  better  incinerated  after 
previous  charring  at  the  lowest  possible  temperature  than 
by  rapid  carbonisation  or  direct  ignition  in  the  flame.  How 
advantageous  it  is  to  char  previously  very  slowly  may 
best  be.  seen  on  incinerating  filters  whose  contents  im- 
pede the  complete  combustion  of  the  paper  by  the  old  pro- 
cess,\-e.ff.  silicic  acid,  ammonio-magnesium  phosphate,  &c. 
Charred  paper  obtained  by  rapid  heating  is  deep  black 
and  of  a  silky  lustre,  whilst  if  slowly  carbonised  it  is 
brownish-black,  dull,  and  smoulders  away  like  tinder. 
Charred  paper  of  the  first  kind  appears  under  the  micro- 


INCINERATING   PRECIPITATES.  89 

scope  perfectly  amorphous,  whilst  the  other  displays  the 
carbonaceous  skeleton  of  the  fibre. 

A  careful  removal  of  precipitates  from  the  filter — with 
the  exception  of  cases  like  zinc  and  cadmium,  where 
volatile  reduction- products  may  be  formed — is  quite  use- 
less, since  the  errors  which  it  was  hoped  to  obviate  are 
not  really  avoided.  On  incineration  with  the  filter,  wet 
or  dry,  an  error  due  to  reduction  may  be  easily  corrected, 
e.g.  in  barium  sulphate  with  sulphuric  acid ;  in  lead 
sulphate  with  nitric  and  sulphuric  acid ;  in  iron  and 
copper  oxides  with  nitric  acid ;  in  silver  chloride  with 
nitric  and  hydrochloric  acids,  &c. 


40  CALCINATION. 


CHAPTER  HI. 

GENERAL  PREPARATORY  CHEMICAL  OPERATIONS. 

CALCINATION. — Strictly  speaking  the  term  calcination 
means  the  production  of  an  oxide  or  Calx  by  combustion, 
and  it  necessarily  involves  the  intervention  of  atmospheric 
oxygen.  But  in  a  metallurgical  sense  the  term  is  re- 
stricted to  the  separation  of  any  volatile  matter  from  a 
mineral  substance  by  the  aid  of  heat  alone,  the  atmosphere 
being  totally  or  partially  excluded ;  or  the  production  of 
rapid  changes  of  temperature,  so  as,  for  instance,  to  render 
minerals  more  fragile  by  heating  and  then  quenching  in 
water  &c. 

Thus  we  speak  of  the  calcination  of  minerals,  as  iron 
or  zinc  ores,  &c.,  whose  matrices  are  argillaceous,  to  expel 
water,  and  also  of  gypsum  to  expel  water ;  the  carbonates 
of  lime,  iron,  copper,  and  lead  are  calcined  to  separate 
carbonic  acid  ;  the  hydro-carbonates  of  zinc  and  iron,  to  get 
rid  of  both  water  and  carbonic  acid  ;  cobalt  and  nickel  ores, 
&c.,  to  separate  arsenic  and  sulphur.  The  iron  ores  found 
in  the  vicinity  of  collieries  are  calcined  to  expel  bituminous 
matter,  and  wood  and  bones  to  expel  volatile  organic  matter. 
Where  the  operation  is  accompanied  by  combustion,  and 
requires  the  oxygen  of  the  atmosphere,  it  is  termed  roasting. 

Crucibles  are  conveniently  used  in  calcination,  as  no 
stirring  of  the  mass  is  required.  They  may  be  made  of 
various  materials,  as  clay,  plumbago,  platinum,  silver,  and 
iron.  Silver  must  not  be  employed  when  sulphur  is  pre- 
sent or  at  a  heat  greater  than  dull  redness.  The  selection 
of  the  crucibles  must  depend  upon  the  substance  under 
operation  ;  they  must  all  be  furnished  with  covers. 


CALCINATION.  4l 

In  almost  all  operations  in  assaying  it  is  necessary  to- 
estimate  the  amount  of  volatile  matter  lost  by  calcina- 
tion. A  very  high  temperature  is  seldom  required  in  cal- 
cination ;  usually  an  air-furnace  will  give  enough  heat. 
When  the  operation  is  finished  the  crucible  must  be 
removed  from  the  fire  and  allowed  to  cool  gradually. 
When  completely  cold,  remove  the  cover  and  take  out 
the  contents  by  means  of  a  spatula.  If  any  adhere,  a  small 
brush  will  be  found  very  useful  for  its  removal.  The 
difference  in  weight  before  and  after  calcination  will 
represent  the  volatile  matter. 

When  the  subject  to  be  calcined  is  fusible,  the  crucible 
and  contents  must  be  weighed  before  ignition  ;  the  loss  of 
weight  is  equal  to  the  quantity  of  volatile  matter  expelled  ; 
in  fact,  this  latter  is  usually  the  most  satisfactory  method 
of  conducting  the  experiment. 

If  the  ignited  substance  be  soluble  in  water,  it  can  be 
removed  from  the  crucible  by  that  menstruum,  employing 
heat  if  required  ;  if  not,  any  suitable  acid  may  be  used. 

If  the  substance  to  be  calcined  decrepitates  on  heating, 
it  must  be  previously  pulverised,  and  heated  slowly  and 
gradually  in  a  well-covered  crucible. 

Certain  substances,  as  lead  carbonate,  undergo  a 
material  alteration  by  contact  with  the  gases  given  off 
during  the  combustion  of  the  fuel  in  the  heating  furnace  ; 
others,  such  as  carbonaceous  matters,  are  consumed  by 
the  introduction  of  atmospheric  air.  All  such  substances 
must  be  calcined  in  a  closely  covered  crucible  placed  in  a 
second  crucible  (also  covered)  for  further  protection. 

In  some  rare  cases,  however,  these  precautions  are  not 
sufficient.  In  such,  either  a  weighed  porcelain  or  German 
glass  retort  must  be  employed. 

Sometimes  earthenware  crucibles  lined  with  charcoal 
are  employed  in  calcination ;  for  even  if  the  substance  be 
fusible  it  may  generally  be  collected  and  weighed  without 
loss,  as  very  few  bodies  either  penetrate  into  or  adhere 
to  a  charcoal  lining.  In  this  way  grey  cobalt  and  other 
arsenic-sulphides  are  calcined  at  a  high  temperature  to 
expel  the  greatest  possible  amount  of  arsenic  and  sulphur. 


42  ROASTING   ORES. 

The  selection  and  proper  management  of  crucibles  will 
be  given  in  the  next  chapter. 

ROASTING. — In  this  operation  carbon,  sulphur,  selenium, 
antimony,  and  arsenic  are  separated  from  certain  metals 
with  which  they  were  combined.  Boasting  differs  from 
calcination  in  this  particular  :  the  latter  is  carried  on  in 
close  vessels,  independent  of  the  atmosphere  ;  the  former, 
in  open  vessels  by  the  aid  of  the  atmosphere.  It  is  thus 
we  are  enabled  to  separate  the  bodies  just  mentioned  by 
this  process ;  for  the  oxygen  of  the  air,  by  combining 
with  them,  forms  a  volatile  substance  which  the  heat 
expels.  Thus,  in  roasting  copper  and  iron  sulphide 
(copper  pyrites),  the  sulphur,  copper,  and  iron  mutually 
combine  with  oxygen  to  form  sulphurous  anhydride  (vola- 
tile), copper  protoxide,  and  iron  peroxide,  thus  : — 

2  (FeS  +  CuS)  +  130  =  Fe203  +  2(CuO)  +  4(S02). 

This  is  the  final  change  in  this  case.  During  the  process, 
however,  some  copper  and  iron  sulphates  and  sub-sul- 
phates, are  formed.  This  change  will  be  explained  under 
the  head  of  Copper  Assay. 

When  carbonaceous  matters  are  roasted,  the  operation 
also  takes  the  name  combustion,  or  incineration ;  because 
the  object  of  roasting  a  fuel,  for  instance,  is  generally  to 
ascertain  the  amount  of  ash  left. 

In  roasting,  in  the  ordinary  acceptation  of  the  term, 
the  body  must  not  be  fused,  but  kept  in  a  pulverulent 
state  ;  there  are,  however,  some  cases  in  which  fusion  is 
.allowable,  as  in  cupellation  and  scorification. 

The  process  of  roasting  is  performed  in  different  ways. 
In  one,  a  small  flat  vessel,  called  a  roasting-test  (fig.  14), 
is  employed,  made  of  the  same  material  as  the  earthen 
crucibles,  and  similar  to  a  saucer.  It  is  most  conveniently 
heated  in  a  muffle.  The  substance  to  be  roasted  must 
be  finely  pulverised,  placed  in  the  roasting  vessel,  and 
constantly  stirred  with  an  iron  or  glass  rod  until  no  fumes 
are  given  off,  or  until  it  ceases  to  evolve  the  odour  of 
sulphurous  acid  if  sulphur  is  one  of  the  constituents 
to  be  eliminated. 


ROASTING   ORES.  43 

The  operation  may  also  be  performed  in  a  crucible,  in 
"which  case  it  must  be  inclined  to  the  operator,  so  that  the 
•draught  of  air  passing  to  the  furnace  flue  may  impinge  as 
much  as  possible  on  the  substance  under  manipulation. 

During  roasting  the  heat  must  be  carefully  regulated 
for  some  time.  At  first  it  ought  only  to  be  the  dullest 
red ;  and  the  substance  must  be  assiduously  stirred  in 
order  to  present  the  largest  possible  surface  to  the  action 
of  the  atmosphere  and  prevent  fusion,  for  some  assays, 
when  roasting,  will  fuse  readily  at  a  low  temperature 
unless  the  surface  be  continually  renewed.  Even  by 
paying  the  utmost  attention  to  this  point  it  cannot  be 
always  prevented,  as  for  instance  when  antimony  sulphide 

FIG.  14. 


is  being  roasted.  In  these  cases  the  assay  must  be  mixed 
with  its  own  weight  of  powdered  quartz  or  fine  white 
sand  (silver  sand)  ;  the  operation  will  then  proceed 
steadily. 

If  the  assay  at  all  agglutinates  it  must  be  taken  from 
the  fire  and  rejected  if  the  substance  be  plentiful ;  if  not, 
the  fused  mass  must  be  carefully  removed  from  the  cru- 
cible or  test,  pulverised,  and  the  roasting  recommenced. 
In  this  case,  however,  the  operation  is  always  very  tedious, 
and  the  final  result  less  exact,  so  that  great  care  ought  to 
be  taken  at  the  commencement  of  the  roasting. 

When  the  assay  has  been  kept  at  a  dull  red  heat  for 
isome  time,  and  shows  no  signs  of  agglutination,  the  heat 
may  be  slightly  increased  ;  at  the  same  time  stirring  must 
be  diligently  pursued.  After  the  heat  has  arrived  at  full 
redness  there  is  little  fear  of  fusion  ;  and  as  the  operation 


44  ROASTING    ORES. 

proceeds  more  rapidly  at  a  high  temperature  than  at  a  low 
one,  it  is  well  now  to  increase  the  heat  to  a  yellowish  red, 
and  even  in  certain  cases  to  nearly  a  white  heat.  If  the 
stirring  of  the  assay  has  been  constant  during  the  various 
gradations  of  heat,  the  roasting  at  this  point  will  be  ac- 
complished ;  and  the  remaining  operations  of  the  assay 
may  be  proceeded  with. 

This  is  the  general  plan  of  operation,  but  different  sub- 
stances require  for  roasting  a  different  degree  of  heat ;  for 
instance,  copper  pyrites  require  a  higher  temperature  than 
grey  copper  ore,  and  the  heat  employed  must  in  every 
case  be  adapted  to  the  substance  to  be  roasted.  Some 
substances,  for  instance,  arseniates,  lead  sulphate,  &c., 
cannot  be  roasted  by  heat  alone.  These  require  the  ad- 
dition of  a  carbonaceous  body  to  remove  the  combined 
oxygen,  and  allow  the  arsenic,  sulphur,  &c.,  to  be  com- 
pletely roasted  off.  Ammonium  carbonate  in  some  cases  is 
also  added  to  the  mixture  to  separate  the  sulphates  formed 
during  the  roasting  of  sulphides. 

In  cases  where  the  metallic  bases  of  the  sulphides  are 
volatile,  either  as  such,  or  as  oxides,  as  for  instance  galena, 
antimony  sulphide,  &c.,  a  loss  of  metal  will  always  result 
during  the  roasting  process. 

It  may  be  as  well  to  mention  here  that  platinum  cap- 
sules are  useful  in  certain  roasting  operations.  The  copper, 
iron,  and  molybdenum  sulphides  are  conveniently  oxidised 
in  this  kind  of  vessel,  without  much  fear  of  injury,  pro- 
vided fusion  of  the  roasting  substance  be  carefully  avoided. 
Platinum  vessels  should  also  be  used  in  ascertaining  the 
amount  of  ash  in  coal. 

REDUCTION. — The  process  of  reduction  consists  in  re- 
moving oxygen  or  an  analogous  element  from  any  body  con- 
taining it,  usually  by  means  of  either  carbonaceous  matter, 
hydrogen,  or  a  body  containing  both  these  elements,  and 
leaving  the  metal  behind,  usually  in  the  form  of  a  melted 
button.  The  rationale  of  the  operation  is  as  follows,  when 
lead  oxide  is  reduced  with  carbon : — 

2(PbO)  +  C  =  2Pb  -f  C02. 


REDUCTION.  45 

In  this  case  we  start  with  lead  oxide  and  carbon,  and  as  a 
result  we  obtain  metallic  lead  and  carbonic  acid. 

The  reaction  between  nickel  oxide  and  hydrogen  is 
thus  expressed  : — 

MO  +  2H  =  M  +  H20. 

Here  we  have  at  the  commencement  nickel  oxide  and 
hydrogen ;  and  after  the  conclusion  of  the  operation  there 
remains  metallic  nickel,  and  water  which  has  volatilised.  If 
the  reducing  substance  contain  both  carbon  and  hydrogen 
the  action  will  be  thus,  when  a  metal  (e.g.  lead)  is  reduced 
from  its  oxide,  carbonic  acid  and  water  being  formed  : — 

3(PbO)  +  CH2  =  3Pb  +  CO  2  +  H20 

In  the  operation  of  reduction  by  the  aid  of  carbona- 
ceous matters  two  methods  are  employed  :  in  the  one, 
charcoal,  coal,  sugar,  starch,  or  any  carbonaceous  or  hy- 
dro-carbonaceous body,  as  argol,  is  mixed  with  the  sub- 
stance to  be  reduced  ;  in  the  other,  the  process  of  cemen- 
tation is  employed.  Where  sulphides  are  to  be  reduced, 
metallic  lead  or  iron  is  usually  employed  to  remove  the 
sulphur.  Generally,  however,  the  sulphides  are  previously 
converted  into  oxides  by  the  operation  of  roasting,  and 
the  reduction  is  then  effected  by  means  of  carbonaceous 
matter. 

The  process  of  cementation  is  conducted  by  placing 
the  oxide  to  be  reduced  in  a  crucible  lined  with  charcoal, 
and  covering  it  closely  while  it  is  in  the  furnace  ;  the  re- 
duction proceeds  gradually  from  the  outside  of  the  oxide 
to  the  centre  of  the  mass.  The  time  requisite  for  this 
operation  depends  on  three  circumstances — viz.  the  nature 
of  the  oxide,  the  degree  of  temperature,  and  the  mass 
acted  on. 

Some  oxides  treated  this  way  are  reduced  very  readily ; 
others,  again,  take  a  considerable  time  ;  while  certain 
of  them  do  not  appear  to  be  acted  on  beyond  the  outer- 
most layer.  Of  the  first  class  is  nickel  oxide ;  of  the 
second,  manganese  oxide  ;  and  of  the  third  and  last,  chro- 
mium oxide. 


46  FUSION. 

Each  of  these  classes  of  reduction  has  its  advantages. 
The  former,  or  reduction  by  mixture  with  carbonaceous 
matter,  takes  place  very  quickly  and  completely,  but  the 
reduced  metal  is  often  mixed  with  carbon ;  in  the  latter 
process  the  residue  is  comparatively  pure,  but  it  is  not 
generally  preferred,  on  account  of  the  time  and  high  tem- 
perature necessary. 

Eeduction  by  hydrogen  gas  is  very  seldom  employed  ; 
it  is,  however,  necessary  in  some  cases,  as  for  instance  in 
the  determination  of  the  percentage  of  cobalt  or  nickel  in 
a  sample,  where  perfect  accuracy  is  desirable.  The  opera- 
tion is  carried  on  in  a  tube  of  hard  German  glass,  having 
a  bulb  blown  in  its  centre,  which  is  heated  either  by  a 
spirit  or  gas  lamp.  Attached  to  it  is  a  tube  full  of  dried 
calcium  chloride,  through  which  the  hydrogen  gas  effect- 
ing the  reduction  passes  to  perfectly  dry  it. 

The  bulb  tube  is  weighed  and  the  oxide  introduced  into 
it ;  it  is  again  weighed,  and  the  apparatus  united  by  caout- 
chouc tubes ;  hydrogen  gas  (see  Reducing  Agents)  is  then 
passed  through  it  until  the  whole  of  the  atmospheric  air 
is  expelled.  Heat  is  afterwards  applied  till  the  bulb  is 
bright  red,  and  the  current  of  gas  continued  until  no  more 
water  from  the  decomposition  of  the  oxide  is  formed  ;  the 
source  of  heat  is  then  removed,  and  the  current  of  gas 
continued  until  the  apparatus  is  cold.  The  bulb  tube, 
with  the  reduced  metal,  is  then  weighed,  and  the  amount 
which  it  has  lost  represents  the  oxygen  which  the  hy- 
drogen has  removed.  By  subtracting  this  oxygen  from 
the  original  weight  of  the  substance,  the  difference  gives 
the  amount  of  metal  in  the  amount  of  oxide  operated  on. 

FUSION. — This  operation  is  sufficiently  simple,  and  is 
employed  in  all  assays  by  the  dry  way,  in  order  to  obtain, 
in  conjunction  with  the  last  process,  a  button  or  prill,  as 
it  is  termed,  of  the  metal  whose  assay  is  in  progress.  It  is 
also  a  necessary  step  in  the  granulation  of  metals,  the 
preparation  of  certain  fluxes  and  alloys,  also  lead  for  the 
assay  for  silver,  in  order  that  a  homogeneous  ingot  may 
be  obtained.  Some  ores,  such  as  those  of  copper,  are 
melted  instead  of  being  roasted  or  calcined,  in  order  to 


SOLUTION.  47 

prepare  them  for  reduction.  Minerals  are  also  melted  per 
se,  or  with  the  addition  of  borax  or  sodium  carbonate,  in 
order  to  ascertain  the  best  treatment  to  be  adopted  in  a 
subsequent  operation.  Metals  too  are  frequently  melted 
to  drive  off  other  volatile  metals  ;  in  this  case  the  heat 
should  be  continued  for  some  time,  and  should  be  very 
high,  as  it  is  difficult  to  remove  the  last  traces  of  volatile 
metals.  Thus,  in  melting  the  spongy  gold  left  behind  in 
the  retort  after  the  distillation  of  gold  amalgam,  the  ingot 
of  gold  almost  always  retains  mercury,  which  can  only  be 
removed  by  repeated  meltings  at  a  very  high  temperature. 
In  some  cases  the  fusion  is  intended  to  be  only  partial, 
the  object  being  to  melt  out  an  easily  fusible  part  of  the 
mineral — for  instance,  in  assaying  grey  antimony  ore  and 
different  bismuth  ores. 

SOLUTION. — In  all  cases  where  analysis  in  the  wet  way 
is  required,  the  mineral  must  be  either  wholly  or  partially 
brought  into  the  state  of  solution.  The  choice  of  a  solvent 
necessarily  depends  upon  the  nature  of  the  material  under 
treatment.  In  some  few  cases  water  will  be  sufficient ;  but 
in  the  majority  acids  are  required.  Sometimes  advantage 
will  be  derived  by  first  extracting  all  that  water  will  dis- 
solve, and  then  applying  acids  to  the  residue.  In  speaking 
of  the  minerals,  &c.,  which  require  solution  for  their  assay, 
the  most  appropriate  solvents  will  be  pointed  out.  In  all 
cases  heat  promotes  solution. 

Solution  is  best  effected  in  glass  flasks  ;  clean  Florence 
oil  flasks  are  very  appropriate  for  most  purposes.  They 
may  be  supported  on  a  hot  sand  bath,  or  on  a  metal  ring 
or  coarse  wire  gauze,  over  the  naked  gas  or  spirit-flame. 
The  flask  should  then  be  placed  in  a  sloping  position,  so 
that  when  the  liquid  boils  or  effervesces  from  the  escape  of 
gas,  the  drops  spirted  up  may  strike  against  the  sloping 
side,  and  run  back  into  the  liquid  instead  of  being  thrown 
out  of  the  mouth. 

A  porcelain  dish  may  also  be  used,  although  from  the 
great  surface  exposed  these  vessels  are  more  appropriate 
for  evaporation  than  solution.  Beakers  may  likewise  be 
employed,  but  they  should  be  covered  over  with  an  in- 


48 


GLASS  AND   PLATINUM   FORCEPS. 


verted  funnel  sufficiently  large  to  rest  within  the  top  edge 
without  slipping  down  more  than  about  half  an  inch  ;  or 
a  large  watch-glass  or  dial-plate  turned  concave  side  up- 
wards may  be  used  as  a  cover.  Both  the  funnel  and  dial- 
plate  serve  the  double  object  of  keeping  out  dust  and 
preventing  loss  of  the  liquid  by  projection  of  fine  drops 
during  ebullition. 

In  many  cases  solution  of  the  whole  or  part  of  a 
mineral  must  be  preceded  by  its  fusion  at  a  high  tempera- 
ture with  sodium  carbonate,  nitre,  or  some  other  flux. 
The  fused  mass  must  then  be  well  extracted  by  boiling 
water,  when  the  residue  will  usually  be  found  soluble  in 
hydrochloric  or  other  acid.  Special  instructions  in  this 

method  of  effecting   solu- 

^- — ^  tions  will  be  given  in  those 

1  c  °  /  1 c  °  J  cases  where  it  is  necessary. 

I  II  Where  it  is   necessary 

II  1          ll          to  manipulate   in    acid  or 

$  \  11          other   solutions,  the   glass 

|1  l::l         and  platinum  forceps   de- 

||  I    1        scribed  by  David   Forbes, 

1  F.B.S.,  in  the  'Chemical 
News  '  for  October  2, 1868, 
will  be  found  useful. 

The  accompanying 
woodcut,  Fig.  15,  shows 
them  in  front  and  side 
view,  and  will  require  but 
little  explanation.  They 
are  made  as  follows  :  an 
ordinary  pair  of  strong 
surgical  forceps  are  taken 
and  the  points  cut  off;  a 
small  piece  of  sheet  brass, 
bent  into  a  cylinder,  is 
then  soldered  to  each  arm 
as  shown  at  a  ;  these  cylin- 
ders being  formed  by  merely  bending  the  brass  round,  so 
as  to  leave  an  open  slit  about  one  twentieth  of  an  inch 


DISTILLATION.       .  49 

wide  in  front.  Two  glass  rods,  such  as  are  used  for 
stirrers,  as  long  as  the  glass  arms  of  the  forceps  are  in- 
tended to  be,  and  just  as  thick  as  will  enter  these  brass- 
cylinders  when  pressed  with  some  force,  are  rounded  by  the 
blow-pipe  at  the  one  end,  whilst  the  other,  when  softened, 
is  somewhat  flattened  between  the  glassblower's  pliers,  as 
seen  in  the  woodcut.  In  order  to  complete  the  forceps  it 
is  now  only  necessary  to  push  each  of  these  rods  into  its 
corresponding  brass  cylinder  or  socket,  the  longitudinal 
slits  of  which,  by  imparting  a  certain  amount  of  elasticity 
to  the  sockets,  cause  them  to  grasp  the  glass  rods  firmly, 
and  retain  them  without  any  cement  or  other  fixing.  The 
relative  lengths  of  the  arms  are  easily  adjusted  by  slipping 
one  rod  more  or  less  forward,  whilst  the  points  can  be 
made  to  hold  and  meet  accurately,  by  rubbing  them  down 
on  a  piece  of  sandstone. 

Such  forceps  may,  of  course,  be  made  to  any  convenient 
size ;  the  one  figured  in  the  woodcut  is  drawn  to  exactly 
half-size,  and  is  found  to  be  cif  very  useful  dimensions  for 
general  analytical  work,  especially  when  manipulating  in 
nitro-hydrochloric  acid,  nitrate  of  silver,  and  other  solutions 
which  would  have  acted  upon  metals,  horn,  ivory,  &c. 

Fig.  16  represents  another  convenient  form  of  forceps, 
also  drawn  to  one  half  the  real  size,  with  long  platinum 
points  soldered  to  the  steel  body  at  a  ;  these  have  been 
also  found  of  great  service  in  general  laboratory  operations, 
especially  when  hydrofluoric  acid  is  in  question. 

DISTILLATION. — There  are  two  distinct  classes  of  this 
operation :  in  the  one,  liquids  are  submitted  to  experiment 
with  the  object  generally  of  separating  them  from  sub- 
stances which  are  non-volatile,  and  will  consequently  be 
left  behind  when  the  liquid  comes  over.  Belonging  to 
this  class  may  be  mentioned  the  distillation  of  nitric  acid, 
the  preparation  of  distilled  water,  and  the  separation  of 
mercury  from  gold  and  silver  amalgam.  In  the  other 
kind  of  distillation,  which  goes  by  the  name  of  dry  distil- 
lation, solid  bodies,  as  wood,  coal,  &c.,  are  subjected  to 
heat  in  order  generally  to  ascertain  the  amount  of  gas  or 
other  volatile  matter  given  off  in  the  course  of  an  experi- 

E 


50 


DISTILLATION, 


FIG.  17. 


T 


ment,  from  a  certain  quantity  of  the  coal  or  other  sub- 
stance operated  upon. 

In  liquid  distillation  (as  in  the  purification  of  nitric 
acid,  &c.),  retorts  are  used.    The  best  form  for  general  use 

is  that  which  is  furnished 
with  a  stopper  at  the  upper 
part  of  the  body,  a  (fig. 
17),  through  which  the 
liquid  is  introduced  ;  the 
neck  of  the  retort  is  then 
placed  in  that  of  a  receiver, 
£,  over  which  a  piece  of 
wet  cotton  or  woollen  cloth 
is  placed,  and  which  must 
be  kept  cold  by  means  of 
a  stream  of  water  from  a 
funnel,  c,  the  shaft  of  which  is  partially  plugged  up  with 
cotton  wool.  Heat  is  then  applied  to  the  retort,  and  as 
much  of  the  liquid  as  is  desired  is  distilled  over  into  the 

FIG.  18. 


receiver.  It  is  advisable  not  to  fill  the  retort  more  than 
two  thirds  full,  and  to  apply  the  heat  at  first  very  gently, 
otherwise  there  is  a  risk  of  breaking  the  vessel. 

A  more  convenient  form  of  apparatus  for  distillation 
and  condensation  is  shown  at  fig.  18,  in  which  a  Liebig's 


DISTILLATION. 


51 


condenser  is  attached  to  the  retort.     Fig.  19  will  show 
the  construction  of  the  condensing  apparatus.     The  cold 


FIG.  19. 


water  passes  into  the  funnel  above,  is  conveyed  at  once 
to  the  lowest  end  of  the  condenser,  whilst  the  heated  water 
passes  off  by  the  upper  tube. 

Distilled  water  is  a  most  important  agent  in  the  labora- 
tory ;  and,  as  much  is  needed,  it  is  better  to  have  a  still 


FIG.  20. 


specially  adapted  for  its  production.  Such  a  one  is  de- 
picted at  fig.  20,  where  A  is  the  body  of  the  still ;  B  the 
furnace  in  which  it  is  set  (the  still  may  also  be  placed  in 
the  portable  furnace,  fig.  25,  p.  63) ;  C  the  still  head  ;  D  E 
the  neck ;  F  the  worm  \IJKL  worm-tub  containing 
cold  water  to  condense  steam  generated  in  still ;  MN  pipe 
to  lead  fresh  cold  water  to  bottom  of  worm-tub,  while  the 
warm  water  runs  off  at  the  top,  as  in  Liebig's  condenser  ; 
and  P  the  vessel  in  which  the  distilled  water  is  received. 

E    2 


52  SUBLIMATION. 

In  the  dry  distillation  of  bodies,  earthenware,  glass,  or 
iron  retorts  are  employed  ;  but  for  small  operations  a  tube 
of  wrought-iron,  about  one  inch  internal  diameter,  and 
plugged  at  one  end,  is  found  to  be  a  convenient  form  of 
apparatus.  It  is  placed  with  the  substance  contained  in  it 
in  a  furnace,  and  a  small  tube,  either  of  glass  or  pewter, 
is  fixed  by  means  of  a  perforated  cork  to  the  open  end  of 
the  large  tube.  The  gas  given  off  during  the  operation 
may  be  collected  by  the  aid  of  the  pneumatic  trough. 

SUBLIMATION. — -This  operation  is  a  kind  of  distillation  in 
which  the  product  is  obtained  under  the  solid  form.  The 
apparatus  which  may  be  employed  for  this  purpose  are 
tubes,  flasks,  capsules,  or  crucibles.  Florence  flasks  are 
exceedingly  useful ;  they  may  be  sunk  in  a  sand-bath,  and 
the  sublimed  substance  received  directly  into  another  flask, 
or  by  passing  through  an  intermediate  tube.  Sometimes, 
however,  it  is  difficult  to  entirely  remove  the  sublimed  sub- 
stance ;  and  in  order  to  avoid  this  inconvenience,  Dr.  lire 
has  proposed  the  following  very  excellent  subliming  appa- 
ratus :  It  consists  of  two  metallic  or  other  vessels,  one  of 
which  is  flatter  and  larger  than  the  other.  The  substance 
to  be  sublimed  is  placed  in  the  smaller  vessel,  and  its 
opening  is  covered  by  the  larger  filled  with  cold  water, 
which  may  be  replaced  from  time  to  time  as  it  becomes 
hot.  The  sublimed  substance  is  formed  on  the  lower  part 
of  the  upper  vessel.  A  large  platinum  crucible,  filled  with 
cold  water,  and  placed  on  the  top  of  a  smaller  one,  answers 
the  purpose  of  the  before-mentioned  apparatus  very  well. 

SCORIFICATION — CuFELLATiON. — These  operations  will  be 
-described  under  the  head  of  Silver  Assay. 


FURNACES.  &31 


CHAPTEE  IV. 

PRODUCTION   AND   APPLICATION   OP   HEAT. 

FURNACES  for  assay  purposes  may  be  heated  either  by  solid 
fuel,  oil,  or  gas,  and  they  may  be  divided  into  wind  and 
blast  furnaces.  In  the  former  the  fire  is  urged  by  the  or- 
dinary draught  of  a  chimney,  and  in  the  latter  by  means 
of  bellows  or  artificial  blast.  We  shall  commence  with  the 
former,  as  they  are  in  most  common  use.  They  are  of 
various  kinds,  according  to  the  purposes  for  which  they  are 
required.  The  three  principal  kinds  are  those  for  fusion, 
calcination,  and  cupellation.  Coal,  coke,  and  charcoal 
are  the  fuels  employed,  and  the  merits  of  each  will  be  par- 
ticularly discussed.  Blast  furnaces  are  only  employed  for 
the  purpose  of  fusion,  although  their  forms  are  various ; 
charcoal  and  coke  are  the  fuels  most  in  use,  but  oil  and  gas 
blast  furnaces  are  used  in  small  laboratory  operations,  and 
for  many  purposes  they  are  preferable  to  other  furnaces, 
on  account  of  their  freedom  from  dust  and  dirt,  and  the 
perfect  control  the  operator  possesses  over  the  heat. 

Furnaces  consist  of ,  certain  essential  parts — viz.  first, 
the  ash-pit,  or  part  destined  to  contain  the  refuse  of  the 
combustible  employed ;  secondly,  the  bars  on  which  the 
fuel  rests  ;  these  are  sometimes  made  movable,  or  are  fixed 
to  a  frame  ;  the  former  arrangement  is  more  convenient, 
as  it  allows  clinkers  and  other  refuse  matters  to  be  readily 
removed ;  thirdly,  the  body  of  the  furnace  in  which  the 
heat  is  produced ;  and  lastly,  in  wind  furnaces,  the  chimney 
by  which  the  heated  air  and  gaseous  products  of  combus- 
tion are  carried  off. 

CALCINING  FURNACE. — Calcining  furnaces  are  small  and 
shallow,  because  a  high  temperature  is  not  required.  They 


54  CALCINING   FURNACES. 

may  be  made  square  or.  circular  ;  the  former  are  most 
readily  constructed,  and,  where  many  crucibles  are  to  be 
heated  at  once,  they  are  preferable  to  the  circular ;  but  the- 
latter  give  the  greatest  degree  of  heat  with  the  least  pos- 
sible consumption  of  fuel,  and  are  to  be  preferred  on  that 
account  where  one  crucible  only  is  to  be  ignited. 

The  body  of  the  furnace  is  best  made  with  good  bricks, 
lined  with  Welsh  lump,  fire-bricks,  or  a  mixture  of  S tour- 
bridge  clay  and  sand.  It  is  also  desirable  that  a  plate  of 
iron  with  a  ledge  be  placed  over  the  upper  part  of  the 
furnace  to  protect  the  brickwork  from  blows  with  crucible 
tongs.  &c.,  and  to  keep  it  in  its  place  when  disturbed  by 
sudden  alterations  of  temperature.  The  bars  of  the  fur- 
nace may  be  either  in  one  single  piece,  or  made  up  of 
several  bars  of  iron  fastened  to  a  frame.  They  ought  to 
be  as  far  as  practicable  from  each  other,  and  must  not  be 
too  large,  although  large  enough  not  to  bend  under  the 
weight  of  the  fuel  and  crucibles  when  they  become  hotr 
and  they  must  not  be  so  far  removed  from  each  other 
as  to  allow  the  coke  or  charcoal  to  fall  through  easily. 
Lastly,  the  more  readily  the  air  can  find  access  to  the 
centre  of  the  fuel,  the  higher  will  be  the  temperature  pro- 
duced in  the  furnace  ;  very  simple  assays  occasionally  fail, 
only  because  the  bars  are  either  too  large  or  too  close 
together. 

CHIMNEY. — Calcining  furnaces  generally  have  no  fixed 
chimney,  but  are  covered  with  a  movable  one  when  a 
greater  degree  of  heat  is  required.  This  chimney  may  be 
about  five  feet  high,  the  diameter  of  the  furnace  at  the 
bottom,  and  tapering  off  to  about  two  thirds  of  that  dia- 
meter at  the  top.  It  is  made  of  strong  plate  iron,  fur- 
nished with  a  wooden  handle.  The  lower  part  is  provided 
with  a  door,  by  means  of  which  the  interior  of  the  furnace 
may  be  examined  without  disturbing  the  whole  arrange- 
ment of  the  chimney,  and  consequent  cooling  of  the  con- 
tents of  the  furnace. 

If,  during  the  course  of  any  experiment,  noxious  or 
offensive  vapours  are  expected  to  be  given  off,  the  furnace 
must  be  so  arranged  that  they  may  be  introduced  into  a 


WIND   FURNACE.  55 

flue,  by  fastening  a  piece  of  iron  plate  pipe,  furnished  with 
an  elbow  joint,  on  to  the  movable  chimney  before  spoken 
of. 

EVAPORATING  FURNACES. — The  furnaces  just  described 
answer  exceedingly  well  in  the  absence  of  gas,  for  heating 
small  flasks,  evaporating  basins,  &c.,when  surmounted  by 
a  tripod  stand  or  sand-bath.  This  is  necessary,  as  many 
assays  by  the  dry  way  are  preceded  and  followed  by  cer- 
tain operations  in  the  wet  way. 

THE  HOOD. — In  order  to  prevent  certain  gases  or  va- 
pours from  fires,  evaporating  basins,  &c.,  from  entering 
into  the  laboratory,  a  large  metal  covering,  termed  a  hood, 
is  employed,  terminating  in  a  chimney  having  a  good 
draught.  It  is  best  made  of  plate  or  galvanised  iron. 

FUSION  FURNACE — WIND  FURNACE. — The  wind  furnace, 
properly  so  called,  is  a  furnace  provided  with  a  chimney, 
and  capable  of  producing  a  very  high  temperature. 

Wind  furnaces  are  generally  square,  but,  if  more  than 
four  crucibles  are  to  be  heated  at  one  time,  they  may  be 
made  rectangular,  the  chimney  being  placed  at  one  of  the 
long  sides.  When  the  furnace  is  required  to  hold  but  one 
pot,  it  may,  however,  be  made  circular. 

The  body  of  the  furnace  ought  to  be  made  of  good 
bricks,  solidly  cemented  with  clay,  and  bound  by  strong 
iron  bands.  The  bricks  must  be  very  refractory,  and 
capable  of  sustaining  changes  of  temperature  without 
cracking.  They  are  ordinarily  made  with  the  clay  used 
in  the  manufacture  of  crucibles.  In  some  cases  bricks  are 
not  used  for  the  lining  of  this  kind  of  furnace ;  for  in- 
stance, a  mould  of  wood  is  placed  in  the  centre,  and  the 
open  space  between  the  surface  of  that  and  the  outer  brick- 
work is  filled  with  a  paste  of  very  refractory  clay,  each 
layer  being  well  beaten  down.  When  the  space  is  filled  the 
case  is  withdrawn,  and  the  crust  of  clay  dried  with  much 
precaution,  every  crack  that  may  be  caused  by  unequal 
desiccation  being  filled  up  as  fast  as  formed.  This  method 
of  manufacture  is  very  applicable  to  circular  furnaces.  In 
every  case,  however,  it  is  necessary  to  border  the  edge 
with  a  band  of  iron  to  prevent  injuries  from  tongs  or  pots. 


66  WIND    FURNACE. 

By  using  a  mixture  of  1  part  of  refractory  clay  and  3  to 
4  parts  of  sifted  quartz  sand,  no  cracks  are  formed  during 
desiccation.  This  mixture  is  used  on  the  Continent  for  the 
interior  fittings  of  Sefstrom's  blast  furnace,  as  well  as  for 
larger  blast  furnaces  for  manufacturing  purposes.  It  is 
said  to  stand  a  high  temperature  exceedingly  well. 

Makins  *  recommends  for  small  furnaces  the  second 
kind  of  bricks,  known  as  Windsor,  or  in  the  trade  P.P 
bricks.  '  These  are  of  a  red  colour,  very  siliceous,  but  soft, 
easily  cut  and  shaped,  and  yet  standing  heat  very  well. 
The  best  method  of  cutting  them  is  by  a  piece  of  zinc 
roughly  notched  out  as  a  saw,  and  then  the  more  accurate 
figure  required  may  readily  be  given  them  by  grinding 
upon  a  rough  flat  stone.  In  this  way  the  small  circular 
furnace  formerly  made  by  Newman,  and  sold  by  him  as 
his  "  universal  furnace,"  is  lined  by  cutting  the  bricks  with 
care  to  the  radii  of  the  circle  they  are  to  form,  when  they 
key  in,  like  an  arch,  and  so  need  no  lining  whatever.' 

THE  ASH-PIT  is  an  open  space  under  the  bars,  which 
serves  as  a  receptacle  for  ashes,  clinkers,  &c.,  produced 
during  the  time  the  furnace  is  in  use.  It  should  have  the 
same  area  as  the  furnace,  and  be  completely  open  in  front, 
so  that  the  air  may  have  free  access  ;  it  is  well,  however, 
for  the  sake  of  economy,  to  furnish  this  opening  with  a 
hinged  door,  having  a  register  plate  fixed  in  it,  so  that  the 
draught  may  be  reduced,  or  entirely  shut  off,  in  order  that 
the  fire  may  be  extinguished  when  desirable,  and  fuel 
saved  which  would  otherwise  be  burnt  in  waste. 

On  the  one  hand,  it  is  well  to  have  the  power  of  cut- 
ting off  access  of  air  into  the  body  of  the  furnace  by  the 
lower  part,  either  to  put  out  the  fire  entirely,  or  to  deaden 
it  whilst  putting  in  a  pot-;  and,  on  the  other,  to  attain  the 
maximum  of  temperature,  we  must  have  the  means  of 
allowing  the  air  to  pass  with  the  greatest  possible  facility 
into  the  furnace.  In  order  to  do  this  it  is  necessary  to 
furnish  the  ash-pit  with  doors,  or  valves,  whereby  the 
quantity  admitted  may  be  regulated  as  desired.  It  is  ad- 
vantageous to  lead  the  air  to  the  ash-pit  from  a  deep  and 

*  Makings  Metallurgy,  p.  88.  <-  '«7' 


WIND    FURNACE. 


57 


cold  place,  by  means  of  a  wide  pipe.  A  chimney  of  less 
height  will  then  be  required. 

THE  BARS  are  made  in  one  piece,  or  are  made  up  of 
movable  pieces  of  metal ;  the  latter  arrangement  is  the 
most  convenient.  Wherever  a  wind  furnace  is  in  use,  the 
superior  opening  is  closed  by  a  cover  made  of  a  fire- tile, 
encircled  with  iron. 

THE  CHIMNEY  is  a  very  essential  part  of  a  wind  furnace : 
it  is  on  its  height  and  size  that  the  draught  depends,  and, 
in  consequence,  the  degree  of  heat  produced  within  the 
furnace.  In  general,  the  higher  and  larger  the  chimney, 


FIG.  21. 


the  stronger  is  the  draught ;  so  that,  by  giving  it  a  great 
elevation,  exceedingly  high  temperatures  may  be  obtained. 
But  there  is  a  limit  which  it  is  useless  to  pass  in  a  furnace 
destined  for  operations  by  the  dry  way  ;  and,  besides  this, 
the  building  a  very  high  chimney  presents  many  difficulties 
and  much  expense,  so  that  in  laboratory  operations,  where 
a  very  strong  current  of  air  is  required,  recourse  is  had  to 
a  pair  of  double  bellows.  A  temperature  can  be  produced 
in  a  wind  furnace  sufficiently  strong  to  soften  the  most 


68  WIND   FURNACE. 

refractory  crucibles,  by  means  of  a  chimney  from  thirty- 
six  to  forty  feet  high. 

Chimneys  are  generally  made  square  or  rectangular,, 
and  have  interiorly  the  same  dimensions  as  the  body  of 
the  furnace.  About  two  feet  above  the  upper  part  of  the 
furnace  they  are  furnished  with  a  register  or  damper,  by 
means  of  which  the  current  of  air  may  be  regulated  or 
entirely  stopped  at  will.  The  damper  is  a  plate  of  iron 
sliding  into  a  small  opening  across  the  chimney. 

A  wind  furnace  of  the  kind  above  described  is  repre- 
sented by  fig.  21. 

The  left-hand  figure  in  21  is  the  plan,  the  middle  and 
elevation,  and  the  right  is  a  sectional  view.  A  the  body 
of  the  furnace  in  which  the  crucibles  to  be  heated  are 
placed,  G  the  bars,  and  Pthe  ash-pit ;  the  cover  is  formed 
of  a  thick  fire-tile  of  the  requisite  size,  firmly  encircled  by 
a  stout  iron  band,  and  furnished  with  a  handle  for  con- 
venience in  moving  it ;  B  the  flue,  C  the  chimney,  R  the 
damper ;  H  a  hood  over  the  furnace,  supported  by  iron 
bands  h  h  h  ;  M  the  handle  of  a  ventilator  T,  which  serves- 
to  carry  off  hot  air  and  fumes  from  furnace  when  open  ; 
and  finally,  S,  a  small  sand-bath,  in  which  to  set  the  red- 
hot  crucibles  when  taken  from  the  fire ;  one  foot  square 
inside  the  fireplace  of  the  furnace  is  a  good  and  convenient 
size  ;  the  remainder  will  then  be  in  proportion. 

BLAST  FURNACES. — In  this  species  of  furnace  the  air 
necessary  to  keep  up  the  combustion  is  forced  through  the 
fuel  by  means  of  a  blowing  apparatus,  instead  of  being 
introduced  by  the  draught  of  a  chimney  as  in  the  wind 
furnace. 

The  most  convenient  apparatus  for  forcing  air  into  a. 
furnace  is  a  double  bellows  ;  a  fan  may  be  used,  but  it  is 
not  so  powerful. 

The  quantity  of  air  passing  into  a  furnace  varies  with 
the  length  of  the  assay,  and  ought  to  increase  gradually 
as  the  temperature  becomes  higher. 

The  following  is  the  description  of  a  most  excellent 
blast  furnace  which  has  been  in  use  for  some  years  in  the 
laboratory  of  the  Eoyal  Institution :  The  temperature 


BLAST   FUKNACE.  59 

produced  by  it  is  extraordinary,  considering  the  small 
amount  of  time  and  fuel  employed.  It  is  sufficiently 
powerful  to  melt  pure  iron  in  a  crucible  in  ten  to  fifteen 
minutes,  the  fire  having  been  previously  lighted.  It  will 
effect  the  fusion  of  rhodium,  and  even  pieces  of  pure 
platinum  have  sunk  together  into  one  button  in  a  crucible 
subjected  to  its  heat.*  All  kinds  of  crucibles,  including 
the  Cornish  and  Hessian,  soften,  fuse,  and  become  frothy 
in  it ;  and  it  is  the  want  of  vessels  which  has  hitherto  put 
a  limit  to  its  application.  The  exterior  (fig.  22)  consists 
of  a  black-lead  pot,  eighteen  inches  in  height,  and  thir- 
teen inches  in  external  diameter  at  the  top  ;  a  small  blue- 
pot  of  seven  and  a  half  inches  external  diameter  at  the  top 
has  the  lower  part  cut  off  so  as  to  leave  an  aperture  of 
five  inches.  This,  when  put  into  the  larger  part,  rests 
upon  its  lower  external  edge,  the  tops  of  the  two  being 
level.  The  interval  between  them,  which  gradually  in- 
creased from  the  lower  to  the  upper  part,  is  filled  with 
pulverised  glass-blowers'  pots,  to  which  22 

enough  water  has  been  added  to  moisten 
the  powder,  which  is  pressed  down  by 
sticks,  so  as  to  make  the  whole  a  com- 
pact mass.  A  round  grate  is  then 
dropped  into  the  furnace,  of  such  a  size 
that  it  rested  about  an  inch  above  the 
lower  edge  of  the  inner  pot ;  the  space 
beneath  it,  therefore,  constitutes  the  air- 
chamber,  and  the  part  above,  the  body 
of  the  furnace.  The  former  is  7^  inches  from  the  grate 
to  the  bottom,  and  the  latter  7^  inches  from  the  grate  to 
the  top.  Finally,  a  longitudinal  hole,  conical  in  form,  and 
1^  inch  in  diameter  in  the  exterior,  is  cut  through  the 
outer  pot,  forming  an  opening  in  the  air-chamber  at  the 
lower  part,  its  use  being  to  receive  the  nozzle  of  the  bel- 
lows by  which  the  draught  is  thrown  in. 

Sefstrom's  blast  furnace,  obtainable  at  most  chemical- 
instrument  makers,  is  also  very  powerful  and  convenient ; 
it  consists  of  a  double  furnace.  It  is  made  of  stout  sheet- 

*  Faraday. 


60  CUPEL   FURNACE, 

iron,  lined  with  fire-clay,  and  is  used  with  coke,  or  char- 
coal and  coke,  broken  into  pieces  of  about  a  cubic  inch  in 
size.  The  blast  of  air  is  supplied  by  a  powerful  blowing- 
machine.  It  will  readily  produce  a  white  heat.  Indeed 
the  limit  to  its  power  seems  to  be  the  difficulty  of  finding 
crucibles  or  interior  furnace  fittings  which  will  stand  the 
temperatures  produced  in  it  without  softening.  Kersten 
states  that  he  increases  the  heat  in  Sefstrom's  blast  furnace 
by  using  a  hot  blast. 

H.  Ste-Claire  Deville  has  employed  for  melting  platinum 
a  furnace  of  30  centim.  height,  and  28  centim.  wide,  which 
rests  upon  a  cast-iron  plate  full  of  holes.  This  is  connected 
with  a  forge  bellows.  After  blowing  for  a  few  minutes, 
the  temperature  of  the  furnace  will  have  reached  the 
highest  possible  degree,  but  this  zone  of  maximum  heat 
only  extends  to  a  small  height  above  the  bottom  of  the 
furnace.  Above  this  point  a  considerable  quantity  of  car- 
bonic oxide  gas  is  formed,  which  burns  with  a  very  long 
flame.  The  heat  produced  in  this  furnace  is  so  high  that 
the  best  crucibles  melt,  and  only  crucibles  made  of  good 
and  well-burned  lime  can  be  used. 

THE  MUFFLE  OR  CUPEL  FURNACE  is  a  furnace  in  the  centre 
of  which  is  placed  a  small  semi-cylindrical  oven,  which  is 
termed  the  muffle.  These  furnaces  were  in  use  as  early 
as  the  thirteenth  century.  Their  construction  and  dimen- 
sions depend — 

1.  On  the  temperature  which  the  furnace  is  intended 
td  produce  ; 

?  2.  -On  the  number  of  cupellations  required  to  be  per- 
formed at  one  time  ;  and 

3.  On  the  kind  of  fuel  to  be  used. 

The  muffles  are  mostly  made  of  refractory  clay,  gene- 
rally of  one  piece,  but  it  is  best  to  make  them  of  two  pieces  ; 
the  bottom  being  one,  and  the  cover  or  vault  the  other. 

Muffles  are  sometimes  made  of  cast-iron,  cast  in  one 
pie<2e.  ~  They  are  useful  in  small  furnaces  intended  for 
cupellations  only. 

Muffle  furnaces  must  always  be  provided  with  a  good 
chimney  to  carry  off  the  hot  gases. 


CUPEL   FURNACE.  61 

The  muffle,  being  completely  surrounded  by  ignited 
fuel,  acquires  a  very  high  temperature,  and  in  its  interior 
all  operations  requiring  the  presence  of  air,  and  which 
cannot  be  carried  on  in  contact  with  carbonaceous  matters, 
may  be  performed — such  as  roastings,  scorifications,  and 
cupellations. 

-When  from  ten  to  twenty  cupellations  have  to  be 
effected  at  one  time,  large  brick  furnaces  are  employed  ; 
and,  in  consequence,  much  fuel  is  consumed  to  waste  in 
these  when  only  a  few  cupellations  are  required.  This 
has  occasioned  many  persons  to  endeavour  to  form  small 
furnaces,  where  one  or  two  cupellations  may  be  carried 
on  with  the  smallest  possible  quantity  of  fuel. 

MM.  Aufrye  and  d'Arcet  have  contrived  a  furnace 
which  is  capable  of  fulfilling  all  these  conditions. 

The  furnace  is  elliptical,  about  7  inches  wide  and  18 
high ;  its  ash-pit  has  but  one  circular  opening,  and  its 
height  is  such  that,  when  the  furnace  is  placed  upon  it, 
and  the  whole  upon  a  table,  the  assay er  can,  when  seated, 
readily  observe  the  course  of  the  assay  within  the  muffle. 
The  hearth  has  five  openings,  in  one  of  which  the  muffle 
is  placed  ;  in  another  a  brick  to  support  it ;  a  third  is  for 
the  purpose  of  introducing  a  poker  to  stir  the  ashes,  and 
make  them  fall  through  the  grate-holes  :  this  can  be  closed 
with  a  small  earthen  plug  ;  and  lastly,  there  are  two  round 
holes,  placed  in  its  largest  diameter,  to  facilitate  the  in- 
troduction of  air,  either  by  draught  or  a  pair  of  bellows, 
as  the  case  may  require.  The  support  for  the  fuel  is 
generally  a  plate  of  earthenware,  pierced  with  holes,  and 
bound  round  with  iron  wire  to  keep  it  together  in  case  it 
cracks  by  changes  of  temperature  ;  but  it  is  better  to  use 
an  iron  grating. 

The  dome  of  the  furnace  has  a  circular  opening,  which 
can  be  closed  by  a  plug  of  earthenware ;  this  opening 
serves  for  the  introduction  of  the  fuel.  A  chimney  is 
necessary  to  increase  the  draught ;  it  is  made  of  sheet-iron, 
and  may  be  from  1^  to  2  feet  in  height,  and  ought  to  fit 
the  upper  part  of  the  dome  very  exactly.  At  its  base 
there  is  a  small  gallery,  also  of  sheet-iron,  in  which  it  is 


Silver 

Lead 

Time 

Standard 

Charcoal 

employed, 

employed, 

of  assay, 

used, 

grains 

grains 

minutes 

thousandths 

grains 

1 

4 

12 

947 

173 

1 

4 

11 

950 

86 

1 

4 

13 

949 

93 

1 

4 

10 

949 

60 

62  CUPEL   FURNACE. 

intended  to  place  the  new  cupels,  so  that  they  may  be 
strongly  heated  before  introduction  to  the  muffle.  This 
saves  many  of  them  from  fracture. 

MM.  Aufrye  and  d'Arcet  have  estimated  the  quantity 
of  charcoal  necessary  to  heat  this  furnace.  The  following 
are  comparative  experiments  : — 

No. 

1 
2 
3 
4 

Coke  or  charcoal  may  be  used  in  this  furnace,  but  the 
fire  must  be  lighted  by  means  of  charcoal  alone,  as  coke  is 
very  difficult  to  inflame  in  a  cold  furnace.  When  it  is  red- 
hot  it  may  be  fed  with  coke,  or,  better  still,  a  mixture  of 
coke  and  charcoal. 

"Where  great  numbers  of  cupellations  have  to  be  made 
at  once,  the  following  form  of  brick  furnace  is  requisite  : — 

Fig.  23  shows  an  elevation  of  the  furnace ;  fig.  24 
shows  a  section.  The  interior  of  the  furnace  is  of  fire- 
brick ;  the  exterior,  of  common  brick.  The  upper  part  is 
protected  by  a  plate  of  iron,  and  the  superior  opening, 
through  which  the  fuel  is  introduced,  is  covered,  when 
necessary,  by  a  large  fire-tile  strongly  encircled  with  an 
iron  band,  to  which  are  attached  two  handles,  by  which 
the  whole  can  be  moved. 

The  muffle  opening,  as  seen  partially  open  in  the  dia- 
gram, can  be  entirely  closed  by  means  of  two  sliding  doors, 
made  of  sheet-iron,  running  in  a  stout  wrought-iron  frame, 
built  into  the  brickwork.  Immediately  below  the  muffle 
entrance  are  two  movable  bricks ;  these  close  the  openings 
through  which  the  fire-bars  are  introduced ;  and  still 
lower  down  is  the  ash-pit  door,  furnished  with  a  register 
for  the  better  regulation  of  the  current  of  air  required  by 
the  furnace.  In  fig.  24  is  shown  a  brick  built  into  the 
back  of  the  furnace,  on  which  the  close  end  of  the  muffle 
is  supported.  This  brick  may,  however,  be  replaced  by  a 
crucible  or  fire-brick  standing  on  the  bars  of  the  furnace. 

A  very  useful  furnace  for  small  operations  is  one  which 


UNIVERSAL   FURNACE.  63 

lias  been  aptly  termed  the  'universal  furnace,'  as  it  is 
-capable  of  performing  all  that  is  required  of  any  furnace 


FIG.  23. 


FIG.  24. 


in  an  assay  (see  figs.  25  and  26,  elevation  and  section).     It 
Is  much  to  be  recommended  for  its  durability,  cheapness, 


FIG.  25. 


FIG.  26. 


and  its  small  size  compared  with  the  heat  it  can  produce. 
It  is  constructed  externally  of  sheet-iron,  very  stout,  and 


64  FURNACE    OPERATIONS. 

is  lined  with  fire-brick,  not  cemented  together,  but  ground 
and  keyed  as  an  arch,  so  that  it  can  never  fall  out  till  it 
is  completely  useless.  Its  height  is  about  2^  feet  and 
diameter  1  foot ;  internal  diameter  8  inches  and  depth  of 
fireplace  1^  feet.  It  is  furnished  with  five  doors,  one  in 
the  ash-pit  and  four  in  the  body  of  the  furnace,  two  in  the 
front,  one  above  the  other,  and  two  opposite  each  other,, 
at  the  sides.  The  cover  serves  as  a  sand-bath,  and  when 
that  is  taken  off  there  is  a  series  of  cast-iron  rings,  fitting 
the  top  of  the  furnace,  where  basins  can  be  placed 
either  for  the  purpose  of  evaporation,  calcination,  or 
roasting.  The  two  opposite  holes  serve  for  the  introduc- 
tion of  a  tube  in  operations  where  it  is  requisite  to  pass  a 
gas  over  any  body  at  a  red  heat.  In  the  lower  hole  in 
front  can  be  placed  a  muffle  for  roastings  and  cupellations,. 
introducing  fuel  and  crucibles  by  the  upper  one ;  it  also 
serves  as  an  opening  through  which  the  state  of  the  fur- 
nace can  be  seen,  or  the  progress  of  any  assay  observed. 

Iron,  manganese,  nickel,  and  cobalt  can  be  fused  in 
this  furnace  when  it  has  a  flue  of  about  thirty  feet  in 
height  attached  to  it,  and  by  closing  the  ash-pit  door,  the 
dullest  red-heat,  for  gentle  roastings,  can.be  obtained. 

FURNACE   OPERATIONS. 

Crucibles  must  be  carefully  supported  in  the  fire,  and 
must  always  be  covered.  They  must  stand  solidly,  and 
be  at  equal  distances  from  the  sides  and  bottom  of  the 
furnace,  so  as  to  receive  a  like  share  of  heat,  and  they 
must  be  completely  surrounded  with  fuel.  If  a  crucible 
is  supported  on  the  grate-bars  of  a  furnace,  the  draught 
of  cold  air  will  prevent  the  bottom  from  getting  hot.  If 
it  is  supported  on  the  fuel,  the  bottom  gets  heated  quickly, 
but  the  fuel  on  burning  away  allows  the  crucible  to  fall 
down,,  and  may  cause  the  loss  of  the  contents.  For  these 
reasons  a  crucible  should  always  be  supported  on  a  piece 
of  fire-brick  about  three  or  four  inches  high.  In  many 
cases  an  old  crucible  inverted  will  serve  as  a  convenient 
support.  The  fire  must  be  got  up  gradually,  so  as  to 


FUfiXACE   APPARATUS.  65 

prevent  the  sides  of  the  furnace  and  the  crucibles  within 
from  cracking  from  the  sudden  increase  of  heat.  No  time 
is  saved  by  urging  the  fire  strongly  at  first,  for  crucibles 
are  bad  conductors  of  heat,  and  a  high  temperature  at 
the  commencement  scarcely  causes  the  heat  to  penetrate 
to  the  interior  faster  than  a  moderate  redness.  After  the 
furnace  has  arrived  at  a  full  red  heat,  more  air  may  be 
given,  and  in  from  about  twenty  minutes  to  one  hour 
the  assay  will  be  finished.  During  the  time  that  the  fur- 
nace is  in  full  action,  the  cover  must  be  occasionally  re- 
moved to  add  more  fuel,  if  any  open  spaces  occur  round 
the  crucibles,  also  to  press  the  fuel  close  to  the  pots. 
When  the  pots  are  taken  out  they  may  be  placed  on  the 
anvil  or  in  a  sand-bath,  and  allowed  to  cool  gradually 
before  they  are  broken  to  examine  their  contents. 

In  commencing  a  second  assay  immediately  in  the  same 
furnace,  certain  precautions  must  be  taken  to  insure 
success.  In  the  first  place,  all  ash  and  clinker  must  be 
removed  from  the  grate  by  means  of  a  crooked  poker ; 
secondly,  the  fuel  must  be  pressed  down  firmly  ;  and  lastly, 
a  layer  of  fresh  combustible  must  be  placed  on  the  fire, 
and  before  that  is  ignited  the  crucibles  must  be  arranged 
upon  the  support  and  the  spaces  about  them  be  filled  with 
coke  or  charcoal,  as  the  case  may  be,  and  the  assay  be 
proceeded  with  as  before. 

In  executing  many  assays,  one  after  the  other,  a  great 
saving  of  fuel  is  effected,  for  the  furnace  is  not  allowed 
time  to  cool. 

AUXILIARY  APPARATUS. — Ordinary  assay  furnaces  require 
very  few  instruments  ;  they  are,  firstly,  pokers  or  stirring 
rods,  made  of  stout  bar-iron :  these  may  be  straight,  as  for 
stirring  the  fuel  from  the  top  of  the  furnace,  so  as  to  fill 
up  cavities  formed  by  uneven  combustion  ;  or  curved,  for 
clearing  the  bars  from  below  from  clinkers  and  ashes. 
Straight  and  curved  tongs  are  also  required ;  for  small 
crucibles  the  blacksmith's  common  forge  tongs  are  the 
most  suitable;  tongs  with  semicircular  ends  (see  fig.  27) 
are  very  serviceable  for  larger  crucibles.  The  tongs  a  are 
particularly  adapted  for  removing  large  cupels  or  calcin- 

F 


66 


FURXACE   TONGS. 


ing  tests  from  the  muffle  ;  the  tongs  b  and  c  are  used  for 
lifting  heavy  crucibles  from  the  wind  or  blast  furnace.  In 
case  the  eyes  of  the  operator  are  weak,  it  is  advisable  to 
make  use  of  a  pair  of  deep  neutral-tint  spectacles.  Most 
of  the  radiant  heat  from  the  interior  of  a  furnace  may  be 


FIG.  27. 


cut  off  by  holding  before  the  face  a  large  sheet  of  window 
glass  ;  or  the  operator  may  look  at  the  reflected  image  in 
a  looking-glass,  instead  of  looking  direct  into  the  furnace 
itself.  Some  assayers  recommend  the  use  of  masks  for  the 
face  and  gloves  for  the  hands,  but  these  are  not  needed. 
In  cupel  furnaces,  both  curved  and  straight  pokers  or 
stirring  rods  are  required  ;  also  a  curved  rod  made  of 
lighter  iron,  to  be  used  in  closing  the  sliding  doors,  slightly 
moving  cupels,  &c.  The  tongs  used  vary  in  form  (see 
fig.  28).  a  represents  very  light  elastic  tongs  or  pincers 

FIG.  28. 


employed  in  the  introduction  of  lead  and  other  matters  to 
the  cupel  ;  b  shows  the  tongs  for  holding  the  scorifier ; 
the  curved  part  fits  the  lower  part  of  the  scorifier,  and  the 
upper  or  single  part  passes  over  the  upper  part  of  the 
scorifier,  so  that  its  contents  may  be  emptied  into  the 
proper  mould  without  fear  of  its  slipping  from  the  opera- 


INGOT   MOULDS. 


67 


tor's  grasp ;  c  represents  the  tongs  used  in  moving  cupels  ; 
they  are  slightly  curved,  so  that  the  cupels  from  the  back 
part  of  the  muffle  may  be  removed  without  disturbing  those 


FIG.  29. 


in  front.  Fig.  29  shows  the  plan  and  section  of  the  ingot 
mould,  into  which  the  contents  of  the  scorifiers  are  poured  ; 
it  is  made  of  thin  sheet  iron,  and  the  depressions  for  the 
reception  of  the  fused  lead  slag  and  ore  are  hammered  out. 


FIG.  31. 


Fig.  30  is  a  wr ought-iron  ladle,  in  which  lead   clippings, 
&c.,  are  melted,  in  order  to  obtain  a  fair  average  of  a  large 

quantity  ;  and  fig.  31  represents 
the  ingot  mould  into  which  the 
fused  lead  or  other  metal  is 
poured.  Other  special  apparatus 
will  be  described  under  the  assay 
in  which  they  are  required. 

Furnaces    are    heated    with 
anthracite,    coke,   and    charcoal,    and   sometimes   with  a 

F    2 


68  FUEL   FOE   FURNACE. 

mixture  of  the  two  latter ;  coal  is  very  seldom  employed, 
and  therefore  will  not  be  much  spoken  of;  coke  is  the 
principal  combustible  used  in  assaying.  Calcining  fur- 
naces ought  to  be  heated  with  charcoal  alone,  because 
coke  employed  in  small  quantities  ignites  and  burns  with 
too  much  difficulty.  All  fuel  contains  certain  fixed  matters 
which  remain  after  combustion,  and  which  constitute  the 
ash.  This  ash  fuses  or  agglutinates  together,  and  when  a 
certain  quantity  is  formed,  if  it  be  not  removed,  the  fire 
will  decrease  in  intensity,  and  finally  die  out.  As  all  com- 
bustibles do  not  contain  the  same  amount  of  ash  ;  they 
should  be  carefully  selected ;  those  containing  the  least 
are  to  be  preferred,  in  the  first  place  because,  weight  for 
weight,  they  contain  more  available  fuel,  and  secondly, 
because  they  can  be  used  in  a  furnace  a  longer  time  with- 
out the  formation  of  so  much  clinker.  The  composition 
of  the  ash  likewise  merits  much  attention. 

Charcoal  contains,  in  general,  from  3  to  4  per  cent,  of 
ash,  the  chief  components  of  which  are  lime  and  potash 
carbonates.  Certain  other  matters  are  also  present,  as 
phosphoric  acid,  iron  oxide,  manganese,  &c.,  but  these 
are  in  very  minute  proportions.  The  ash  is  not  fusible 
per  se,  and,  if  it  does  not  meet  with  any  substance  capable 
of  combining  with  it,  it  passes  through  the  bars  as  a  white 
powder  ;  but  when  the  potash  predominates,  it  exercises 
a  corrosive  action  on  the  bricks  with  which  the  furnace  is 
lined,  as  also  on  crucibles,  lutes,  &c.,  by  the  formation  of 
a  fusible  potassium  silicate,  which  in  course  of  time  runs 
down  the  sides  of  the  furnace,  and  chokes  the  bars. 
Whenever  the  ash  is  in  very  small  proportion  to  the 
charcoal,  its  fusion  is  rather  useful  than  otherwise,  be- 
cause it  forms  a  species  of  varnish,  which,  penetrating  the 
surface  of  the  bricks  and  lutes,  gives  them  solidity  by 
binding  them  together  with  a  cement,  forming  part  of 
their  substance. 

The  proportion  of  ash  which  coke  contains  is  very 
variable  ;  some  commercial  samples  contain  from  8  to  10 
per  cent.,  while  others,  made  from  very  pure  coal,  give 
but  2  to  3  per  cent.  ;  so  that  this  fuel  also  ought  to  be 


CHARCOAL — COKE.  (59 

carefully  chosen.  The  nature  of  this  ash  is  different  from 
that  of  charcoal ;  it  consists  principally  of  iron  oxide  and 
clay.  The  former  is  produced  from  the  pyrites  which 
coal  generally  contains.  The  clay  is  similar  to  the  car- 
bonaceous schists,  not  very  fusible  by  itself,  but  neverthe- 
less capable  of  softening.  When  pure,  it  forms  a  slag, 
which  attacks  neither  the  bricks  nor  crucibles.  This 
happens  very  rarely  ;  it  is  more  often  that  iron  oxide 
predominates,  and  this  by  contact  with  the  carbonaceous 
matter  becomes  reduced  to  the  state  of  protoxide,  and  is 
then  not  only  very  fusible,  but  exercises  on  all  argillaceous 
matters  a  very  corrosive  action,  so  that  crucibles  are  very 
seriously  injured,  and  the  sides  of  the  furnace  require 
frequent  repairs. 

Weight  for  weight,  coke  and  charcoal  give  out  nearly 
the  same  quantity  of  heat ;  but  in  equal  bulks,  the  former 
develops  much  more  heat,  because  its  density  is  greater. 
From  this  difference  in  the  calorific  power  of  coke  and 
charcoal,  it  results  that  in  the  same  furnace  the  former 
produces  a  greater  degree  of  heat  than  the  latter ;  and  at 
high  temperatures  the  difference  has  been  proved  to  be 
nearly  10  per  cent.  In  order  to  account  for  this,  we  must 
consider,  firstly,  that  in  a  given  space  the  quantity  of  heat 
produced  in  a  certain  time  (and,  in  consequence,  the  tem- 
perature) depends  on  the  amount  of  fuel  burnt,  and  in- 
creases with  its  weight ;  secondly,  that  combustion  takes 
place  but  at  the  surface  of  the  masses,  whatever  may  be 
the  nature  of  the  fuel ;  from  which  may  be  deduced,  that 
the  weight  of  fuel  burnt  in  an  unit  of  time  ought  to  be 
exactly  proportionate  to  its  density  ;  and  in  consequence, 
the  densest  fuels,  furnishing  the  most  food  for  combustion, 
ought  to  give  out  the  greatest  heat.  But,  as  for  the  same 
reason  they  consume  a  larger  proportion  of  oxygen,  they 
require,  in  order  to  produce  the  maximum  effect,  a  more 
rapid  and  stronger  current  of  air. 

It  is  clear,  from  what  has  been  stated  concerning  the 
relative  properties  of  coke  and  charcoal,  that  when  the 
former  can  be  procured  of  good  quality,  and  especially 
when  the  ash  contains  but  little  oxide  of  iron,  it  ought  to 


70  EFFECTS   OF   FURNACES. 

be  preferred  to'charcoal,  for  assays  requiring  a  high  tem- 
perature. 

This  being  an  important  subject,  it  has  been  thought 
advisable  to  devote  a  special  chapter  to  the  assay  of 
fuel.  S 

A  very  essential  condition  in  obtaining  the  maximum 
effect  of  a  furnace,  the  importance  of  which  can  alone  be 
appreciated  by  experience,  is  to  choose  pieces  of  fuel  of  a 
suitable  size.  If,  on  the  one  hand,  a  shovelful  of  coke  or 
charcoal  be  taken  at  random,  it  generally  contains  the 
dust  and  dirt  found  in  most  fuel,  and  which,  by  filling  the 
interstices,  prevent  the  air  from  passing  as  required,  and 
consequently  render  the  combustion  slow.  On  the  other 
hand,  if  a  furnace  be  filled  with  large  pieces,  considerable 
spaces  are  left  between  them,  so  that  but  a  comparatively 
small  surface  is  exposed  to  the  action  of  the  atmospheric 
oxygen,  and  a  correspondingly  small  quantity  of  fuel  is 
consumed  in  a  given  time  ;  so  that  the  maximum  heat 
can  never  be  obtained.  In  order  to  produce  the  desired 
result,  it  is  necessary  that  the  pieces  shall  have  a  certain 
mean  size,  and  experience  has  proved  that  pieces  about 
1  inch  to  li  inch  diameter  produce  the  best  effect. 
These  may  be  selected  by  sifting  the  coke  through  two 
strong  wire  sieves,  one  of  which  has  meshes  about  1^ 
inch  square,  and  the  other  about  1  inch  square.  The 
coke  which  passes  through  the  larger  one,  but  will  not 
go  through  the  smaller  sieve,  will  be  the  right  size  for  the 
furnace. 

THE  EFFECTS  PRODUCED  BY  WIND  AND  BLAST  FURNACES. — 
Assays  by  the  dry  way  can  be  made  either  in  wind  or 
blast  furnaces.  In  either  of  them,  the  degree  of  heat 
depends  upon  the  volume  of  air  which  passes  through 
the  fuel  in  the  same  time ;  but,  cceteris  paribus,  large 
furnaces  produce  more  heat  than  small  ones,  because 
comparatively  less  heat  is  lost  by  radiation  in  the  former 
than  the  latter. 

In  a  wind  furnace,  the  maximum  of  heat  is  limited  by 
the  size  of  the  chimney,  and  in  a  blast  furnace  by  the 
dimensions  of  the  bellows ;  but  by  weighting  the  latter. 


FOCUS   OF   MAXIMUM   TEMPERATURE.  71 

more  or  less,  the  force  of  the  blast  can  be  increased,  and, 
in  consequence,  the  temperature  to  a  considerable  extent. 
In  this  respect  blast  have  the  advantage  over  wind 
furnaces. 

In  the  latter,  the  draught  increases  in  proportion  as 
the  heat  becomes  more  intense  in  the  furnace,  so  that 
the  temperature  producible  increases  progressively.  In  a 
blast  furnace,  the  bellows  can  be  weighted  and  worked 
as  heavily  as  possible  at  once,  and,  by  opening  all  the 
apertures  for  receiving  air,  the  maximum  temperature  can 
be  produced  more  rapidly  than  in  a  wind  furnace  ;  but 
this  is  of  little  use,  because,  as  heat  passes  very  slowly 
through  the  substance  of  a  crucible,  when  the  object  is 
to  fuse  its  contents  it  must  be  heated  gradually,  so  as 
to  avoid  running  the  risk  of  softening  the  crucible  before 
its  contents  are  acted  upon,  or  even  scarcely  made  warm. 

Wind  furnaces  are,  however,  much  more  serviceable 
and  economical  than  blast,  because  they  work  themselves, 
and  do  not  require  the  service  of  a  man  to  attend  to  the 
bellows.  A  blast  furnace  is  used  in  a  laboratory,  in  cer- 
tain cases ;  for  instance,  when  a  single  crucible  has  to  be 
submitted  to  an  intense  heat,  and  when  the  furnace  is 
small,  and  the  bellows  large,  in  which  case  the  operation 
resembles  a  blow-pipe  assay. 

In  whatever  manner  the  air  is  introduced  into  any 
kind  of  furnace,  whether  wind  or  blast,  it  is  evident  that 
the  quantity  of  heat  developed  in  equal-sized  furnaces 
depends  upon  the  quantity  of  air  introduced  in  the  same 
time ;  but  the  degree  of  temperature  is  not  the  same  in 
different  parts  of  the  furnace,  and  the  distribution  of  heat 
varies  according  to  the  manner  in  which  the  air  is  intro- 
duced into  the  midst  of  the  fuel.  The  side  over  which 
the  air  passes  is  kept  cold  by  the  current,  on  which 
account  fire-bars  last  a  long  time  without  becoming  oxi- 
dised, but  the  heat  rapidly  augments  up  to  a  certain 
distance  from  the  bars,  at  which  place  it  arrives  at  its 
maximum  ;  above  that  it  diminishes  rapidly,  because  the 
air  is  nearly  deprived  of  its  oxygen.  Experiment  has 
proved  that  this  maximum  is  about  2^  to  3  inches  above 
the  bars  or  tuyeres. 


72  OIL   AND    GAS   FURNACES. 

In  common  wind  furnaces  the  air  enters  through  the 
spaces  between  the  horizontal  bars  which  form  the  bottom 
of  the  furnace,  and  the  crucibles  are  placed  on  a  stand 
which  rests  on  these  bars.  By  this  means  the  lower  and 
centre  part  of  the  crucibles,  in  which  parts  the  matter  to 
be  fused  is  placed,  are  exactly  situated  in  the  maximum 
of  heat ;  but  the  stand  being  constantly  kept  cold,  by  the 
contact  of  a  current  of  air,  establishes  a  continual  draining 
or  carrying  away  of  heat  from  the  interior  of  the  crucibles 
outwards,  so  that  the  substance  submitted  to  assay  can 
only  arrive  at  the  maximum  temperature  after  a  length  of 
time,  and  the  maximum  then  is  always  inferior  to  that  in 
the  mass  of  fuel.  It  is  on  this  'account  that  assays  in  a 
blast  or  wind  furnace  generally  occupy  from  one  hour  to 
two  hours.  The  author  has  found  that  the  time  may  be 
reduced  to  half  that  just  stated,  if  a  good  solid  foundation 
of  fuel  be  made,  and  the  crucible  placed  on  that,  and  well 
surrounded  by  coke,  constantly  kept  close  to  the  pot  and 
the  sides  of  the  furnace  ;  in  this  manner  the  cooling  effect 
of  the  stand  is  removed,  and  the  consequent  maximum 
effect  of  the  furnace  is  produced,  but  then  there  is  danger 
of  the  supporting  fuel  being  burnt  away  from  the  crucible 
and  the  latter  getting  upset. 


OIL   AND    GAS   BLAST   FURNACES. 

It  sometimes  happens  that  metallurgists  and  assayers 
have  occasion  to  melt  metals  at  a  white  heat,  but  do  not 
wish  to  heat  a  large  furnace  for  the  purpose.  In  these 
cases  either  the  gas  or  oil  furnaces  now  to  be  described 
will  prove  very  useful. 

OIL  FURNACES. — Mr.  Charles  Griffin,  the  well-known 
chemical  instrument  maker,  has  described  an  oil  lamp, 
which  is  not  only  as  powerful  in  action  as  the  best  ga& 
furnaces,  but  almost  rivals  them  in  handiness  and 
economy. 

DESCRIPTION  OF  THE  APPARATUS. — The  oil-lamp  furnace 
is  represented  in  perspective  by  fig.  32,  and  in  section  by 
fig.  33.  It  consists  of  a  wick-holder,  an  oil-reservoir,  and 


GRIFFINS   OIL   BLAST   FURNACE.  78 

a  fire-clay  furnace ;  to  these  must  be  added  a  blowing- 
machine  for  the  supply  of  atmospheric  air. 

The  oil-reservoir  is  represented  at  a,  fig.  32  ;  it  is 
made  of  japanned  tin-plate,  mounted  on  iron  legs,  and 
fitted  with  a  brass  stop-cock  and  delivery-tube.  Its 
capacity  is  a  little  more  than  a  quart.  The  wick-holder 
is  represented  at  £,  and  the  upper  surface  of  it  by  the 
separate  figure  c,  fig.  34.  The  wick-holder  and  the  oil- 
reservoir  are  consequently  detached,  d  is  a  tube  which 
brings  oil  from  the  runnel  e,  and  /  is  a  tube  to  be  placed 

FIG.  32. 


in  connection  with  the  blowing  apparatus.  The  wick- 
holder  contains  three  concentric  wicks,  placed  round  the 
multiple  blowpipe  c,  which  is  in  communication  with  the 
blowing-tube. 

The  crucible  furnace  consists  of  the  following  parts, 
shown  in  figs.  32  and  33  :  g  is  an  iron  tripod  ;  h  is  a  flue 
for  collecting  and  directing  the  flame.  The  flue  is  of  such 
a  width  that  when  the  wick-holder,  6,  is  pushed  up  into 
it  until  the  top  of  the  wick  is  level  with  the  top  of  the 
clay  cone,  there  remains  a  clear  air-space  of  about  -|-  inch 
all  round  between  the  wick-holder  and  the  cylindrical 
walls  of  the  flue,  i  represents  a  fire-clay  grate  having 


74 


DETAILS   OF   THE    MANAGEMENT   OF   THE 


three  tongues,  shown  by  i  (fig.  34),  on  its  upper  surface. 
These  tongues  support  the  crucible,  without  stopping  the 
rising  flame,  k  is  a  fire-clay  cylinder  which  rests  upon 
the  grate  i,  and  incloses  the  crucible,  forming,  in  fact,  the 
body  of  the  furnace.  Of  this  piece  there  are  three  sizes  : 
the  smallest  is  of  3  inches  bore,  and  works  with  crucibles 
that  do  not  exceed  2f  inches  diameter  ;  a  middle  size, 
4  inches  bore,  for  crucibles  not  exceeding  3f  inches 
diameter ;  the  largest  size,  5  inches  bore,  for  crucibles 
not  exceeding  4f  inches  diameter.  This  piece,  being 
heavy,  is  provided  with  handles,  as  represented  in  p, 


FIG.  33. 


FIG.  34. 


fig.  34.  The  walls  of  the  cylinders  are  from  1  inch  to 
li  inch  thick.  /  is  a  flat  plate  of  fire-clay  with  a  hole  in 
the  centre,  used  to  cover  the  cylinder  &,  so  as  to  act  like 
a  reverberatory  dome  ;  m  is  a  cover  which  prevents  loss 
of  heat  from  the  crucible  by  radiation,  but  gives  egress  to 
the  gaseous  products  of  the  combustion  of  the  oil ;  n  is  an 
extinguisher  to  put  over  the  wick-holder  when  an  opera- 
tion is  ended  ;  and  o  is  a  support  for  the  wick-holder.  No 
chimney  is  required. 

MANAGEMENT  OF  THE  OIL-LAMP  FURNACE The  apparatus 

is  to  be  arranged  for  use  as  it  is  represented  by  fig.  32. 
The  cylinder,  £,  is  to  be  selected  to  fit  the  crucible,  and 


OIL   BLAST   FURNACE.  75 

the  crucible  of  a  size  to  suit  the  quantity  of  metal  that  is 
to  be  melted  :  1  Ib.  of  iron  requires  the  smallest  of  the 
three  cylinders,  described  above  ;  1^  Ib.  the  middle  size  ; 
5  Ibs.  the  largest  size.  The  air-way  between  the  crucible 
and  the  inner  walls  of  the  cylinder  should  never  exceed 
^  inch  nor  be  less  than  ^  inch. 

The  cotton  wicks  must  be  clean,  and  be  trimmed  a 
little  below  the  level  of  the  blowpipe  c.  If  properly 
managed,  they  do  not  readily  burn  away,  but  can  be  used 
for  several  fusions.  The  reservoir  should  be  filled  with 
oil  for  each  operation.  The  proper  sort  of  oil  for  use  is 
the  more  volatile  kind  of  mineral  oil,  of  the  specific 
gravity  of  *750,  which  is  now  easily  procurable  at  about 
three  shillings  per  gallon.  The  variety  known  by  the 
commercial  name  of  turpenzine  answers  well.  The  com- 
bustion of  a  quart  of  this  oil,  costing  ninepence,  gives 
heat  sufficient  to  melt  5  Ibs.  of  cast  iron.  Probably  the 
lighter  kinds  of  paraffin  oil  may  be  suitable.  Liquids  of 
the  alcoholic  class,  spirits  of  wine,  and  pyroxylic  spirit 
can  be  used ;  but  they  are  less  effective  and  more  expen- 
sive than  turpenzine.  Care  must  be  taken  not  to  spill 
the  oil  on  the  table  or  floor,  and  not  to  decant  it  carelessly 
in  the  neighbourhood  of  a  light,  because  atmospheric  air 
strongly  charged  with  the  vapour  of  these  light  oils  is 
explosive.  When  the  oil  is  burnt  in  the  furnace  in  the 
manner  described  below,  there  is  no  danger.  During  an 
operation,  a  wooden  screen,  as  represented  by  the  dotted 
lines  in  fig.  32,  should  be  placed  between  the  oil-reservoir 
and  the  furtiace,  to  prevent  the  vaporisation  of  the  oil  by 
radiant  heat.  As  the  wick-holder  b,  and  the  supply  pipe 
d,  contain  only  about  one  fluid  ounce  of  oil,  the  oil  must 
run  continuously  during  a  fusion,  from  the  reservoir  a, 
into  the  funnel  0,  in  order  that  the  cotton  may  be  always 
flooded.  The  success  of  the  fusion  depends  upon  the  due 
supply  of  oil,  to  which  point  the  operator  must  pay  atten- 
tion. At  the  commencement  of  a  fusion,  the  oil  must  be 
run  from  the  reservoir  until  the  surface  of  the  oil  in  the 
funnel  has  a  diameter  of  about  an  inch.  The  wicks  will 
then  be  flooded,  and  a  light  may  be  applied,  and  a  gentle 


76  THE    OIL   BLAST   FURNACE. 

blast  of  air  then  turned  on.     The  oil  immediately  sinks  in 
the  funnel,  and  the  stop-cock  must  be  opened  and  so  regu- 
lated as  to  keep  the  oil  barely  visible  at  the  bottom  of  the 
funnel.     If  too  much  oil  is  supplied  it  immediately  rises 
in   the   funnel,  and  simultaneously  overflows   the   wick- 
holder.     Too  much  vapour  is  then  thrown  into  the  fur- 
nace, and  the  heat  is  immediately  lowered,  especially  at 
the  beginning  of  an  operation,  before  the  fire-clay  portions 
of  the  furnace  are  well  heated.     If,  on  the  contrary,  too 
little  oil  is  supplied,  the  wicks  burn,  and  the  operation  is 
spoilt.     The  demand  of  the  wick-holder  for  oil  depends- 
upon  the  condition  of  the  furnace  and  the  character  of  the 
fusion  in  progress.     When  the  lamp  is  newly  lighted  and 
the  furnace  cold,  the  oil  should  be  passed  slowly  in  distinct 
drops  ;  but  as  the  furnace  becomes  heated  the  rapidity  of 
the  supply  of  drops  should  be  increased  ;  and  finally,  when 
the  furnace  is  at  a  white  heat,  the  oil  should  be  supplied 
in  a  thin  continuous   stream.     When  the  fusion  to  be 
effected  is  that  of  only  a  small  quantity  of  metal,  such  as 
1  Ib.  of  iron,  a  rapid  supply  of  drops  of  oil  is  sufficient 
even  to  the  close   of  the   operation.      At  that  rate  the 
burner  consumes  about  1^  pint  of  oil  in  an  hour.     When 
the  fusion  to  be  effected  is  that  of  4  Ibs.  or  5  Ibs.  of  iron 
and  the  large  furnace  is  in  action  and  has  been  brought 
to  a  white  heat,  the  supply  of  oil  must,  as  stated  above,  be 
in  a  thin  continuous  stream,  and  the  operation  will  then 
consume  two  pints  of  oil  in  an  hour.    And  here  it  requires 
remark  that,  with  that  continuous  supply,  when  the  fur- 
nace is  large  and  is  at  a  white  heat,  the  oil  does  not  rise 
in  the  funnel,  being  instantaneously  converted  into  gas  at 
the  mouth  of  the  burner,  and  thrown  up  in  that  state  into 
the  furnace  for  combustion.     The  operation,  indeed,  con- 
sists at  that  point  of  a  rapid  distillation  of  oil-gas,  which 
is  immediately  burnt,  in  the  presence  of  air  supplied  at  a 
suitable  pressure  by  a  dozen  blowpipes,  in  effective  contact 
with  the  crucible  to  be  heated. 

The  flame  produced  in  this  furnace  is  as  clear  as  that 
produced  by  an  explosive  mixture  of  air  and  coal-gas.  It 
is  perfectly  free  from  smoke,  and  the  consumed  vapours 


POWER   OP   THE   FURNACE.  77 

which  occasionally  escape  with  gaseous  products  of  a  com- 
bustion, are  even  less  unpleasant  to  smell  and  to  breathe 
in  than  are  those  which  are  usually  disengaged  by  a  blast 
gas  furnace,  or  by  an  ordinary  lamp,  fed  with  pyroxylic 
spirit. 

The  contents  of  a  crucible  under  ignition  in  this  furnace 
<3an  at  any  moment  be  readily  examined,  it  being  only 
necessary  to  remove  the  pieces  I  and  m  with  tongs,  and 
to  lift  the  cover  of  the  crucible,  during  which  the  action 
of  the  furnace  need  not  be  interrupted. 

When  the  operation  is  finished,  the  blast  is  stopped, 
the  stop-cock  is  turned  off,  the  oil-reservoir  is  removed, 
the  wick-holder  is  lowered  on  the  support  0,  withdrawn 
from  the  furnace,  and  covered  with  the  extinguisher  n. 
The  quantity  of  oil  which  then  remains  in  the  lamp  is  about 
one  fluid  ounce. 

POWER  or  THE  OIL-LAMP  FURNACE. — The  furnace  being 
•cold  when  an  operation  is  commenced,  it  will  melt  1  Ib.  of 
-cast  iron  in  25  minutes,  1^  Ib.  in  30  minutes,  4  Ibs.  in  45 
minutes,  and  5  Ibs.  in  60  minutes.  When  the  furnace  is 
hot,  such  fusions  can  be  effected  in  much  less  time  ;  for 
-example,  1  Ib.  of  iron  in  15  minutes.  It  need  scarcely  be 
added  that  small  quantities  of  gold,  silver,  copper,  brass, 
•German  silver,  &c.,  can  be  melted  with  great  ease,  and 
that  all  the  metallurgical  and  chemical  processes  that  are 
-commonly  effected  in  platinum  and  porcelain  crucibles  can 
be  promptly  accomplished  in  the  smallest  cylinder  of  this 
furnace  ;  and  in  the  case  of  platinum  vessels,  with  this 
special  advantage,  that  the  oil-gas  is  free  from  those  sul- 
phurous compounds  the  presence  of  which  in  coal-gas  fre- 
quently causes  damage  to  the  crucibles. 

REQUISITE  BLOWING  POWER. — The  size  of  the  blowing- 
machine  required  to  develop  the  fusing  power  of  this  oil- 
lamp  furnace  depends  upon  the  amount  of  heat  required 
or  the  weight  of  metal  that  is  to  be  fused.  For  ordin- 
ary chemical  operations  with  platinum  and  porcelain 
crucibles,  and  even  for  the  fusion  of  1  Ib.  of  cast  iron  in 
clay  or  plumbago  crucibles,  a  blowing  power  equal  to  that 
of  a  glass-blower's  table  is  sufficient,  provided  the  blast  it 


78  GAS   FURNACE. 

gives  is  uniform  and  constant.  But  the  fusion  of  masses 
of  iron  weighing  4  or  5  Ibs.  can  be  effected  by  the  ga& 
which  this  oil-lamp  is  capable  of  supplying,  provided  a 
sufficiently  powerful  blowing-machine  supplies  the  requi- 
site quantity  of  air.  When  more  than  a  quart  of  oil  is  to 
be  rapidly  distilled  into  gas,  and  the  whole  of  that  gas  is 
to  be  burned  with  oxygen,  it  is  evident  that  effective  work 
demands  a  large  and  prompt  supply  of  air. 

As  in  all  practical  matters  of  this  sort  the  cost  is  a 
main  question,  it  may  be  useful  to  state  that  the  price  of 
this  apparatus  complete,  without  the  blowing-machine,  but 
including  every  other  portion  necessary  for  heating  cruci- 
bles up  to  the  size  sufficient  to  fuse  1  Ib.  of  cast  iron,  is  one 
guinea  ;  and  that  with  the  extra  furnace-pieces  for  cruci- 
bles suitable  for  5  Ibs.  of  iron,  or  any  intermediate  quantity,, 
the  cost  is  one  guinea  and  a  half. 

Mr.  Griffin  has  described  before  the  Chemical  Society 
an  improved  gas  furnace  for  chemical  operations  at  a  white 
heat  without  the  aid  of  a  blowing-machine,  and  a  new 
method  of  supporting  crucibles  in  gas  furnaces.  The  fol- 
lowing extracts  from  his  paper  are  taken  from  the  Journal 
of  the  Chemical  Society  : — 

"  On  a  former  occasion  I  introduced  to  the  notice  of 
the  Chemical  Society  a  gas  furnace  for  operations  at  a 
white  heat  in  crucibles,  or  a  copper-melting  heat  in  muffles. 
A  detailed  description  of  that  furnace  is  given  in  the 
Journal  of  the  Society  for  August  1870.  The  crucibles 
are  either  suspended  in  a  pierced  plumbago  cylinder,  or 
supported  on  a  trivet  grate,  both  of  which  are  liable 
to  break  when  white  hot,  and  therefore  cause  trouble 
and  expense.  Crucibles  vary  so  much  in  form  and  size 
that  they  are  often  not  suspended  from  these  cylinders 
exactly  in  the  focus  of  the  heating  power.  Trivet  grates 
have  the  disadvantage  that  they  interfere  with  the  direct 
action  of  the  flame  upon  the  crucible,  and  if  made  slightly 
they  break  when  heated  to  whiteness.  I  desire  now  to 
place  before  you  a  new  form  of  burner  by  which  these 
defects  are  remedied.  In  the  new  burner  the  circle  of  gas- 
jets  is  enlarged  so  as  to  leave  a  space  round  the  central 


GAS    FURNACE.  79" 

jet.  An  atmopyre  similar  to  those  used  in  Hofmann's 
combustion  furnace,  but  of  greater  bulk  and  strength,  is 
dropped  over  this  central  jet,  and  forms  a  solid  support 
for  the  crucible.  This  support  does  not  readily  break,, 
but,  should  an  accident  happen,  it  can  be  replaced  at  the 
cost  of  a  few  pence.  It  brings  the  bottom  of  the  crucible 
exactly  into  the  focus  of  heat,  and  itself  supplies  a  portion 
of  the  heating  power  of  the  burner.  It  also  enables  one  to 
use  any  crucible  at  hand,  independent  of  its  form  or  size. 
A  strong  lateral  arm  cast  on  the  body  of  the  burner  sup- 
ports an  upright  iron  rod,  which  carries  the  chimney  of 
the  furnace.  By  prolonging  the  legs  of  the  burner  up- 
wards they  are  made  to  carry  the  clay  furnace,  and  thus, 
by  doing  away  with  a  stool  or  other  support,  the  con- 
struction is  simplified  and  the  cost  lessened.  A  plumbago 
cylinder,  to  deflect  the  flame  and  entrap  the  heat,  is  placed 
round  the  crucible,  and  is  covered  with  an  ordinary 
crucible  cover,  by  removing  which  the  crucible  can  be 
inspected.  These  fittings,  however,  present  nothing  new, 
being  adapted  from  Griffin's  blast  gas  furnace,  which  was 
introduced  sixteen  years  ago.  Access  to  the  crucible  in 
the  furnace  is  gained  by  turning  aside  the  chimney  and 
lifting  the  top  plate  of  the  furnace,  which  is  provided  with 
handles  for  this  purpose.  These  handles  do  not  become 
very  hot,  even  when  the  furnace  is  at  a  white  heat.  The 
power  of  these  new  burners  is  very  remarkable,  one  of 
small  size  consuming  only  20  feet  of  gas  per  hour,  and 
having  a  chimney  4  feet  high,  being  capable  of  fusing  half 
a  pound  of  cast  iron  in  35  minutes  from  the  time  of  lighting 
the  gas ;  or  of  melting  gold,  silver,  or  copper  in  crucibles 
placed  within  a  muffle  measuring  5  inches  long  by  3  wide. 
If  a  chimney  6  feet  high  be  employed,  cast  iron  can  be 
melted  in  crucibles  placed  within  the  muffle.  A  burner  of 
larger  size,  consuming  40  feet  of  gas  per  hour,  will  melt 
cast  iron  in  crucibles  placed  within  a  large  muffle  measuring 
8  inches  long  by  4  inches  wide.  In  the  crucible  furnace 
it  will  melt  1  Ib.  of  cast-iron  in  35  minutes,  2  Ibs.  in 
45  minutes,  3  Ibs.  in  55  minutes,  and  4  Ibs.  in  65 
minutes,  from  the  time  of  lighting  the  gas.  It  is  thus. 


80 


GAS    FURNACE. 


seen  that,  when  a  white  heat  has  been  once  obtained, 
10  minutes'  time  is  required  for  the  fusion  of  every 
additional  pound  of  iron.  These  results,  attainable  with 
certainty  and  rapidity,  are,  I  believe,  the  highest  that  have 
hitherto  been  placed  at  the  command  of  the  chemist.  As  in 
my  former  furnace,  the  proper  admixture  of  gas  and  air 
is  judged  of  from  the  colour  and  quantity  of  flame  which 
passes  up  the  chimney.  To  enable  the  operator  to  see 
this  flame,  three  small  holes  are  bored  in  the  chimney. 


FIG.  35. 


FIG.  36. 


The  flame  is  not  seen  at  the  upper  hole,  unless  the  supply 
of  gas  is  too  large,  but  it  is  always  visible  at  both  the 
lower  holes." 

In  the  above  figure  the  muffle  is  provided  with  a  small 
draught  flue,  having  a  regulating  cap  on  its  upper  end. 
In  the  small  furnaces  this  is  omitted,  and  the  muffle  is 
slotted  in  the  usual  manner.  The  cover  of  the  furnace  is 
now  made  without  the  zigzag  opening  in  the  roof.  The 
burner  of  the  muffle  furnace  is  the  same  as  that  used  in 
the  crucible  furnace,  fig.  35. 


GAS   FUKXACE. 


81 


Skittle  pots  up  to  8  inches  can  be  used  in  these  furnaces 
for  collecting  and  burning  waste  with  fluxes,  &c.,  and  in 
much  less  time  than  is  required  by  a  coke  fire.  An  8-inch 
pot  can  be  worked  in  half  an  hour  from  lighting  the  gas. 
Two  of  the  outer  cylinders  are  used,  placed  one  on  the 
top  of  the  other. 

FIG.  37. 


With  a  4-foot  flue  the  muffle  furnace  melts  gold,  silver, 
and  copper  ;  with  a  6-foot  flue  it  melts  cast-iron  placed  in 
crucibles  within  the  muffle.  The  consumption  of  gas  is  20 
cubic  feet  per  hour. 


82  UNIVERSAL    GAS    FURNACE. 

The  Distillation  of  Pure  Zinc,  per  descensum,  can  be 
performed  in  one  of  these  gas  furnaces  by  passing  a  tube 
from  the  top  of  the  crucible  downwards  through  the 
burner  to  the  table. 

Fig.  37  shows  one  of  Griffin's  extra  large  gas  fur- 
naces, capable  of  raising  a  No.  12  plumbago  pot,  measur- 
ing 8  inches  high  by  6  inches  wide,  to  a  white  heat.  The 
cover  of  this  furnace  is  let  into  the  body,  which  rises  higher 
than  in  the  smaller  patterns,  and  from  which  the  flue  passes 
off  laterally  to  a  standing  flue  or  other  house  chimney. 

UNIVERSAL  GAS  FURNACE.  —  Mr.  Thomas  Fletcher  has  de- 
vised what  he  terms  a  universal  gas  furnace  ;  it  works  with- 
out blast,  for  crucible  operations,  up  to  a  clear  white  heat. 

The  specialty  of  this  furnace  is  the  burner.  It  is  as 
simple  and  easy  to  use  as  an  ordinary  Bunsen's  burner,  but 
the  flame  is  solid  to  the  centre,  unlike  the  flame  of  every 
heating  burner  which  has  previously  been  made.  The 
open  flame  will  readily  fuse  a  coil  of  thick  copper  wire, 
and  to  make  a  crucible  furnace  it  simply  requires  a  support 
for  the  crucible,  and  a  fire-clay  jacket  to  prevent  radia- 
tion, as  the  flame  is  in  itself  perfect,  and  requires  no 
blowing  or  attention  in  any  way.  The  furnace  is  so  small 


FIG.  38.     .  that  it  can  be  used  on  the  work- 

bench, and  put  away  on  a  shelf,  and  can 
be  used  on  a  sitting-room  table  without 
the  slightest  dirt  or  inconvenience.  The 
body  of  the  furnace  is  only  6  inches  in 
diameter. 

THE  SINGLE  -  JACKETED  ARRANGEMENT, 
shown  in  section,  fig.  38,  is  capable  of 
melting  5  or  6  oz.  of  gold  in  15  minutes 
with  a  10-inch  chimney,  or  in  10  minutes 
with  a  2  -ft.  chimney.  With  the  ladle- 
holder  it  will  melt  8  Ibs.  of  zinc  in  15 
minutes,  without  chimney,  in  an  ordin- 

ary iron  ladle,  and   lead,'  tin,  &c.,  in   a  proportionately 

shorter  time. 

THE    DOUBLE-JACKETED    CHEMICAL    FURNACE,    shown    in 

section,  fig.   39,  having  the  same  burner  as  above,  and 


FLETCHERS    GAS   FURNACE. 


83 


requiring  no  more  gas,  will  melt  3  or  4  oz.  of  cast-iron 
in  35  minutes,  if  used  with  a  3 -ft.  chimney,  or,  if  with  a 
longer  chimney,  in  a  proportionately  shorter  time,  and 
will  give  any  required  temperature  in  proportion  to  the 
length  of  chimney  used,  provided  the  gas  is  turned  on 
sufficiently  just  to  cover  the  crucible  with  flame  when  the 
chimney  is  in  its  place. 

In  case  of  the  fusion  of  a  crucible,  or  its  penetration 
by  fluxes  when  the  furnace  is  used  for  extremely  high 
temperatures,  no  damage  can  be  done  -to  the  furnace, 
except  perhaps  the  destruction  of  a  few  of  the  burner 


FIG.  39. 


FIG.  40. 


tubes,  which  can  be  replaced  at  a  trifling  expense.     No 
part  of  the  furnace  is  liable  to  injury  with  constant  use 

The  burner  is  shown  in  plan  in  fig.  40.  The  lower 
part  is  a  chamber  6  in.  x  3  in.,  open  at  the  bottom,  in 
which  the  gas  is  partially  mixed  with  air.  This  mixture 
is  conducted  to  the  top  of  the  burner  through  a  mass  of 
fine  tubes,  55  in  number,  with  an  arrangement  to  supply 
between  each  exactly  the  amount  of  air  necessary  to 
consume  it  instantly.  A  flame  produced  by  this  means, 
consuming  20  feet  of  gas  per  hour,  is  only  about  2  inches 
high,  and  almost  colourless.  The  whole  of  the  available 
heat  is  generated  in  the  proper  place,  viz.  below  the 
object  to  be  heated,  which,  therefore,  is  not  also  cooled 
by  the  passage  of  unburnt  gas  and  air.  The  flame  is  very 
similar  in  appearance  to  a  mass  of  blowpipe  jets,  and  has 

G  2 


84  FLETCHER'S  GAS  FUKNACE. 

the  same  heating  power.  The  point  of  greatest  heat 
commences,  as  with  a  blowpipe,  at  the  point  of  the  blue 
cones,  about  \  in.  or  f  in.  above  the  tubes. 

The  Double-jacketed  Chemical  furnace  is  made  to 
take  crucibles  not  exceeding  in  size  No.  00  of  the  Plum- 
bago Crucible  Co.,  which  are  the  most  convenient  for 
melting  quantities  not  exceeding  5  or  6  oz.  of  gold,  &c. 

For  crucibles  put  the  flat  plate  A  (see  fig.  38)  over  the 
centre  of  the  burner,  with  the  three  inner  projecting 
points  upwards.  Place  the  crucible  on  the  projecting 
points.  Be  careful  that  the  points  are  upwards,  or  the 
crucible  will  be  too  low.  Light  the  gas,  and  then  put  on 
the  large  fire-clay  ring  B,  to  surround  the  crucible,  which 
must  be  exactly  in  the  centre  of  the  opening :  then  the 
small  fire-clay  cover,  with  the  iron  tube  upward,  (7,  and 
the  chimney  if  used.  The  gas  must  then  be  turned  very 
gradually  down  until  the  white  part  of  the  flame  dis- 
appears, and  the  flame  covers  the  crucible.  If  the  supply 
of  gas  is  not  sufficient,  it  will  be  found  necessary  to 
examine  the  tap  which  supplies  the  gas,  many  of  which,, 
as  supplied  by  gasfitters,  are  exceedingly  faulty,  and  par- 
tially stopped  up.  If  this  be  the  case,  the  tap  should  be 
replaced  by  a  better  one.  The  furnace  requires  supply 
from  a  -|  or  T7g-  in.  pipe.  If  a  larger  crucible  be  used 
than  the  one  supplied,  an  extra  fire-clay  ring  must  be 
obtained  of  the  same  proportionate  width,  and  half  an 
inch  higher  than  the  top  of  the  crucible. 

,  When  a  white  heat  is  required,  the  crucible  must  be 
covered  with  the  inner  perforated  plumbago  dome,  as 
shown  in  fig.  45,  and  which  forms  the  inner  jacket,  with 
the  perforations  in  such  a  position  that  the  crucible  can 
be  seen  through  the  hole  in  the  lower  part  of  the  chimney  ; 
a  chimney  not  less  than  3  feet  high  must  be  used.  If  a 
greater  heating  power  is  required,  a  longer  chimney  will 
enable  it  to  be  obtained  in  the  same  or  a  shorter  time,  but 
under  all  circumstances  the  flame  must  just  cover  the 
crucible  to  obtain  proper  results. 

Where  the  gas  supply  is  more  than  necessary,  a  longer 
chimney  may  be  used  with  advantage,  but  as  the  furnace 


FLETCHER'S  GAS  FURNACE.  85 

itself  is  too  small  and  light  to  form  a  steady  support  for  a 
longer  chimney,  it  will  be  necessary  to  suspend  the  upper 
part  with  a  wire,  or  to  support  it  with  a  bracket  from  the 
wall.  The  furnace  requires  the  following  supply  of  gas  : 
Without  chimney,  18  cubic  feet ;  with  10-inch  do.,  22 
cubic  ft.  ;  with  36-inch  do.,  28  to  30  cubic  ft.  per  hour. 
If  the  gas  supply  is  deficient,  the  wire  should  in  all  cases 
be  removed  from  india-rubber  tubing,  as  it  interferes 
seriously  with  the  passage  of  gas. 

The  addition  of  the  small  muffle  (E,  fig.  41)  for  high 
temperatures  makes  this  furnace  complete  for  all  purposes. 
The  clear  working  space,  which  is  equally  heated  in  every 
part,  measures  2^  x  2f  x  21  in.  It 
will  be  seen  from  the  engraving  that 
the  muffle  is  not  in  contact  with  the 
outer  casing  in  any  part,  and  therefore 
all  parts  are  equally  heated.  The  tem- 
perature obtained  depends  on  the  length 
of  chimney  used,  provided  the  gas  sup- 
ply is  sufficient  to  cover  the  muffle  with 
flame  when  the  chimney  is  on.  For 
silver  assays  about  4  feet  of  chimney 
should  be  used,  which  gives  the  melting 
point  of  fine  silver  in  16  minutes  from 
the  time  the  gas  is  lighted ;  the  same 
temperature  being  always  obtained  in  exactly  the  same 
time,  within  a  few  seconds ;  and  after  the  first  trial  the 
operation  does  not  require  watching.  With  this  furnace 
there  will  be  found  no  variation  in  a  number  of  assays 
done  at  different  times. 

A  chimney  of  about  6  or  8  ft.  gives  nearly  a  clear 
white  heat  in  30  minutes,  and  for  special  operations 
requiring  very  high  temperatures  a  longer  chimney  may 
be  used  as  required.  A  chimney  or  stove  pipe  10  or  12 
ft.  long  may  be  used  as  a  fixture,  and  the  draught  par- 
tially stopped  with  a  damper  or  slide  when  lower  tempe- 
ratures are  required,  the  gas  being  turned  down  in  pro- 
portion ;  the  guide  for  the  proper  adjustment  being  that 
under  all  circumstances  the  flame  must  just  cover  the 


FLETCHER'S  GAS  FURNACE. 


muffle,  but  must  not  extend  into  the  chimney  so  as  to 
make  it  red  hot. 

It  will  not  be  found  necessary  in  practice  to  partially 
close  the  chimney  for  lower  temperatures,  as  the  same 
effect  may  be  produced  equally  well  by  simply  turning  the 
gas  lower  ;  but  it  is  more  economical  to  partially  stop  the 
draught,  so  as  to  prevent  excess  of  cold  air  being  drawn 
in.  When  the  flame  covers  the  muffle,  the  gas  is  doing 
its  extreme  duty  under  the  most  favourable  circumstances, 
without  waste.  The  same  rule  applies  also  to  the  crucible 
arrangement.  Particles  of  flux  should  not  be  allowed  to 
fall  on  the  fire-clay  casing,  where  the  parts  touch  each 
other  ;  and  the  power  of  the  furnace  should  not  be  urged 
too  far  by  the  use  of  very  long  chimneys,  as  there  is 
danger  of  the  fusion  of  the  fire-clay  parts  together  so  that 
they  cannot  be  separated.  Fire-clay  fittings,  as  a  rule, 
cannot  be  safely  used  for  temperatures  much  exceeding 
the  fusing  point  of  cast  iron. 

Mf.  Fletcher  has  recently  brought  out  a  new  melting 
arrangement  for  melting  up  to  3  oz.  of  gold  or  silver, 

rapidly,  without  the  use 
of  a  furnace. 

The  figure  (42)  is 
slightly  under  half-size. 
In  this  arrangement  the 
two  parts  of  the  ingot- 
mould  slide  on  each  other, 
to  enable  ingots  of  any 
width  to  be  cast.  And 
the  blowpipe  is  part  of 
the  rocking- stand.  Con- 
nect the  blower  to  the 
upper  tube,  and  the  gas 
to  the  lower.  When  the 
metal  is  melted  in  the 
shallow  crucible  of  com- 
pressed charcoal,  tilt  the 
whole  apparatus  over  so  as  to  fill  the  ingot-mould.  A 
sound  ingot  can  be  obtained  in  about  2  minutes.  Very 


FIG.  42. 


FLETCHER  S   GAS   FUBNACE.  87 

bulky  scrap  should  be  run  into    a  mass   in   one  of  the 
moulder  carbon  blocks  before  being  placed  in  the  cru- 
cible.    No  flux  must  be  used  with  the  charcoal  crucibles. 
Mr.  Fletcher  has  also  devised  an  injector  gas  furnace 
(fig.  43)  for  metallurgists,  jewellers,  chemists,  iron,  brass,  and 

nickel  castings,  manu- 

,  JP     ../.•!  FIG.  43. 

lacturers   01   artificial 

gems,  and  other  pur- 
poses where  an  ordin- 
ary furnace  is  useless 
or  unreliable. 

It  has  been  found 
that  in  working  at  ex-  AIR 
tremely  high  tempera- 
tures, the  ring  which 
holds    the    gauze    is 

liable  to  be  fused.  To  prevent  this,  a  new  burner  has  been 
designed,  in  which  the  ring  is  entirely  dispensed  with,  and 
the  gauze  cap  is  pushed  up  from  the  back  of  the  burner 
against  a  small  shoulder  inside  the  nozzle  of  the  burner. 
The  burner  is  in  one  casting,  and  therefore  there  is  no 
tendency  for  the  nozzle  to  get  hot,  as  in  the  former  pat- 
tern. See  that  the  gauze  is  pushed  up  from  behind  to 
within  about  J  inch  of  the  nozzle.  The  power  and  speed 
of  working  are  practically  without  limit,  depending  only 
on  the  gas  and  air  supply,  and  are  under  perfect  control. 
With  ^ -inch  gas-pipe  and  the  smallest  foot-blower,  the 
small  furnace  will  melt  a  crucible  full  of  cast-iron  scrap 
in  7  minutes ;  and  steel  in  12  minutes,  starting  with  all 
cold. 

To  adjust  a  new  furnace  to  its  highest  power,  put 
the  nozzle  of  the  burner  tight  up  against  the  hole  in 
the  side  of  -  the  casing,  turn  on  the  full  gas-supply, 
with  the  ^ir-way  full  open.  If  the  flame  comes  out  of 
the  lid  about  2  inches  the  -adjustment  is  -right.  -  If  the 
flame  is  longer,  enlarge  the  hole  in  the  air-jet  until  the 
proper  flame  is  obtained,  or  reduce  the  gas-supply;  if 
smaller,  or  not  visible,  turn  the  air-check  until  the  flame 
appears. 


88  FLETCHER'S  GAS  FURNACE. 

Keep  all  fluxes  away  from  the  furnace  jacket.  Before 
stopping  the  blower,  draw  the  burner  back  from  the 
hole.  Commence  blowing  before  the  lid  is  put  on  the 
furnace. 

The  old  pattern  blower  is  liable  to  pick  up  dirt  from 
the  floor,  throwing  it  against  the  gauze  of  the  burner,  and 
stopping  the  proper  working  of  the  furnace  until  cleared 
away.  A  thin  layer  of  silver  sand  on  the  bottom  will 
prevent  crucibles  adhering  when  at  a  white  or  blue  heat. 
Crucibles  must  be  heated  very  slowly  the  first  time  they 
are  used,  unless  of  the  '  Salamander  '  brand. 

In  cases  where  gas  cannot  be  obtained,  Mr.  Fletcher  has 
devised  a  simple  furnace  (fig.  44)  for  high  temperatures, 

FIG.  44. 


working  with  either  gas  or  spirit-petroleum  without  altera- 
tion, and  with  perfect  results  with  either  fuel.  This 
furnace  is  supplied  with  a  small,  simple,  and  perfectly 
safe  arrangement  for  burning  the  vapour  of  gasoline  or 
benzoline,  giving  a  power  and  efficiency  fully  equal  to 
that  which  can  be  obtained  by  a  larger  gas-supply.  The 
arrangement  is  in  every  way  as  simple  as  when  gas  is 
used,  requiring  no  more  trouble  or  attention. 

It   equals   a   gas-furnace   in   every   respect,   and,   in 
addition,  gives  a  heat  of  absolute  purity,  fitting  it  for  the 


GORE'S   GAS   FURNACE.  89 

most  delicate  chemical  operations  where  gas  cannot  be 
used  owing  to  the  presence  of  sulphur  and  other  matters. 

The  ordinary  pattern  of  injector  furnace  is  used  in 
precisely  the  same  way  as  with  gas,  the  only  difference 
being  that  a  branch  pipe  is  taken  out  of  the  air  supply 
and  connected  to  the  lower  tap  A  on  the  generator,  and  a 
tube  is  carried  from  the  upper  tap  B  to  the  side  tube  of 
the  injector-burner  marked  '  gas.'  The  quantity  of  vapour 
required  is  adjusted  by  the  lower  tap  A  when  the  furnace 
is  working,  and  the  flame  must  be  just  visible  at  the  hole 
in  the  lid,  exactly  as  when  gas  is  used,  the  instructions 
being  precisely  the  same  for  both  fuels. 

To  charge  the  generator,  pour  benzoline  or  gasoline  in 
the  top  hole  until  it  overflows  at  the  small  tap  C  in  the 
side,  replace  the  cork  firmly,  and  close  the  overflow  tap. 
It  will  then  work  for  about  10  to  12  hours  at  the  full 
power  of  the  furnace. 

Benzoline  varies  much  in  quality ;  it  must,  when  a 
few  drops  are  poured  on  a  plate  or  the  hand,  evaporate 
quickly  and  completely,  leaving  no  greasy  stain,  and  if 
good  will  produce  more  vapour  than  the  furnace  can  burn 
at  its  maximum  power.  All  the  tubing  used  must  be 
perfectly  smooth  inside,  or  the  power  of  the  furnace  is 
greatly  reduced. 

At  the  conclusion  of  an  operation,  close  both  taps  on 
the  generator.  It  can  then  be  left  for  any  length  of  time 
ready  for  instant  use.  For  ordinary  meltings,  the  gene- 
rator can  be  used  about  thirty  or  forty  times  without 
refilling. 

The  No.  3  size  will  refine  and  perfectly  fuse  6  Ibs.  of 
chemically  pure  nickel  so  that  it  can  be  poured  clean, 
using  an  open  crucible,  a  feat  beyond  the  capabilities  of 
any  other  known  furnace. 

Benzoline  often  contains  heavy  oils.  If  the  generator 
works  badly,  empty  it  and  refill  with  fresh. 

G.  Gore,  Esq.,  F.K.S.,  has  devised  a  gas  furnace  which 
will  fuse  cast  iron,  &c.,  and  still  allow  the  melted  sub- 
stances to  be  perfectly  accessible  to  be  manipulated  upon 
for  a  continuous  and  lengthened  period  of  time,  without 


90 


GORE  S   GAS   FURNACE. 


contact  with  impurities  or  with  the  atmosphere,  and  with- 
out lowering  their  temperature  sufficient  to  cause  them 
to  solidify.  These  conditions  Mr.  Gore  has  obtained  by 
means  of  ordinary  coal-gas  and  atmospheric  air^  without 
the  use  of  a  bellows  or  lofty  chimney,  or  of  regenerators 
or  valves  requiring  frequent  attention.  The  arrangement 
is  as  follows  :  A  (figs.  45  and  46)  is  a  cylinder  of  fire-clay 
about  9  inches  high  and  6  inches  diameter,  open  at  both 
ends,  with  a  hole  in  its  side  near  the  bottom  to  lead  into 


Fm.  45. 


FIG.  46. 


the  chimney  ;  it  is  covered  by  a  movable  plate  of  fire-clay, 
B,  with  a  hole  in  its  centre  for  introduction  or  removal  of 
the  crucible,  &c. ;  this  hole  is  closed  by  a  perforated  plug 
of  clay,  "(7,  for  access  to  the  contents  of  the  crucible,  and 
that  again  is  closed  by  another  clay  stopper  D ;  E  is  a 
chimney  of  sheet  iron  about  5  or  6  feet  high,  kept 
upright  by  a  ring  of  iron" F  attached  to  the  top  of  the 
furnace.  The  fire-clay  cylinder  is  enclosed  in  a  sheet  of 


GOEE'S   GAS   FURNACE.  91 

iron  casing  with  a  bottom  of  iron,  to  which  are  fixed 
three  iron  legs  G.  An  iron  tube  H,  with  a  prolongation 
/,  supports  by  means  of  the  screw  J  the  burner  K  and  its- 
tube  L,  which  is  open  at  both  ends.  Gas  is  supplied  to 
the  burner  by  means  of  the  tap  M,  which  has  a  small 
index  N  attached  to  it  for  assistance  in  adjusting  the  gas. 
Inside  the  large  cylinder  is  another  fire-clay  cylinder  or 
cupola  0,  with  open  ends,  and  with  three  projections  of 
fire-clay  P,  for  supporting  the  crucible  Q ;  it  is  kept 
steady  by  means  of  three  clay  wedges  R  ;  S  is  an  air- valve 
for  closing  the  bottom  of  the  tube  Z.  The  gas-burner  is 
a  thin  metal  cylinder,  deeply  corrugated  at  its  upper  end,, 
with  the  corrugations  diminishing  to  nothing  at  its  lower 
end,  as  shown  in  the  engravings.  The  action  of  this 
furnace  is  as  follows  :  Gas  is  admitted  to  the  open  tube  L 
by  the  tap  M ;  it  there  mixes  with  air  to  form  a  nearly 
combustible  mixture,  which  ascends  through  the  burner, 
and  burns  in  the  clay  cylinder  0,  being  supplied  with  the 
remainder  of  air  necessary  to  combustion  through  the 
tube  H  to  the  outer  surface  of  the  flame  ;  the  products  of 
combustion  pass  up  through  the  cylinder  0,  and  then 
downwards  outside  of  it  to  the  chimney,  the  point  of 
greatest  heat  being  at  Q. 

It  is  important  in  using  this  furnace  that  the  burner  be 
placed  quite  in  the  centre  of  the  bottom  of  the  tube  0 ; 
also  that  a  crucible  of  not  too  large  nor  too  small  dimen- 
sions be  selected.  The  most  suitable  way  of  supporting  a 
smaller  crucible  is  by  placing  it  in  a  larger  one  that  has 
had  its  upper  part  broken  off.  If  desirable,  a  little  clay 
luting  may  be  placed  round  the  top  edge  of  the  iron 
casing  to  exclude  air  entering  between  it  and  the  cylinder  ; 
also  a  little  thin  clay  luting  upon  the  part  of  the  bottom  of 
the  furnace  where  the  inner  cylinder  0  rests. 

In  lighting  the  furnace,  the  plugs  (7  and  D  are  removed, 
a  light  held  inside  the  opening,  and  the  gas  turned  on  full. 
Should  the  flame  blow  down  to  the  bottom  of  the  tube  L 
on  lighting  (which,  however,  rarely  occurs  unless  the 
furnace  is  already  hot),  the  gas  must  be  turned  off,  and 
the  bottom  of  L  momentarily  closed  whilst  lighting  the  gas 


92  GORE  S   GAS   FURNACE. 

as  before.  Should  the  flame  not  burn  down  to  the  burner, 
but  only  burn  to  the  orifice  in  the  clay  plate  B>  it  must  at 
once  be  extinguished  and  relighted,  otherwise  some  of  the 
gaseous  mixture  will  pass  into  the  chimney  unburned,  and 
subsequently  ignite  and  cause  an  explosion.  A  large 
flame  now  issues  from  the  top  orifice,  and  is  white  if  too 
much  gas  is  on,  and  chiefly  violet  or  red  with  the  proper 
quantity  ;  it  should  now  be  coarsely  adjusted  until  these 
appearances  are  represented.  The  annular  plug  C  should 
now  be  inserted,  which  will  compel  it  to  pass  downwards 
to  the  chimney,  and  as  soon  as  the  small  remaining  flame 
now  issuing  disappears,  or  nearly  disappears,  as  it  will  in 
a  few  seconds,  the  smaller  stopper  D  should  also  be 
inserted.  In  lieu  of  this,  the  large  flame  may  be  deflected 
against  the  chimney  by  means  of  a  piece  of  sheet  iron  until 
it  withdraws  inwards  as  before  mentioned  ;  the  two  plugs 
may  then  be  reinserted.  The  gas  tap  may  now  be  partly 
adjusted.  The  crucible  should  be  placed  in  the  furnace 
after  the  act  of  lighting  the  gas,  but  not  immediately  after 
if  the  furnace  is  cold,  or  explosions  may  occur  by  un- 
burned gaseous  mixture  passing  the  crucible  into  the 
chimney,  and  igniting  afterwards. 

After  about  five  minutes  the  gas  should  be  slowly  ad- 
justed, until  a  sound  is  heard  inside  like  a  series  of  small 
explosions.  This  sound  is  sometimes  not  very  distinct, 
especially  at  high  temperatures,  and  therefore  requires  a 
little  experience  in  the  use  of  the  furnace  in  order  to  be 
detected.  It  is,  however,  a  chief  guide  in  determining  the 
proper  amount  of  gas,  and  should  therefore  be  carefully 
studied.  To  assist  in  adjusting  the  gas  it  will  be  found 
very  useful  to  place  a  small  piece  of  looking-glass  beneath 
the  tube  Z,  and  to  adjust  the  gas  tap  until  the  flame 
between  the  burner  and  crucible  appears  wholly  violet  or 
slightly  white  ;  but  this  test  is  liable  to  fallacy  if  em- 
ployed when  the  gas  is  first  lighted,  because  the  coldness 
of  the  parts  makes  the  flame  much  whiter  than  it  other- 
wise would  appear.  It  is  also  fallacious,  the  flame 
appearing  whiter  than  it  really  is  when  the  crucible  is 
very  hot.  It  is,  however,  of  great  assistance,  especially  at 


GOKE'S    GAS   FURNACE.  9S 

intermediate  temperatures.  A  rough  deposit  upon  the 
outer  edge  of  the  crucible  indicates  an  excess  of  gas ;  the 
deposit  is  carbon.  Less  gas  is  required  with  a  crucible  in 
the  furnace  than  without  one :  also  less  is  required  when 
the  small  hole  at  the  top  of  the  furnace  is  open  than  when 
it  is  closed  ;  and  less  is  also  required  when  the  furnace  is 
cold  than  after  it  has  been  lighted  some  time,  because  the 
draught  gradually  increases  and  draws  in  more  air.  After 
having  accurately  adjusted  the  gas,  no  further  attention 
to  the  furnace  is  requisite. 

Having  once  found  the  proper  adjustment  of  gas  under 
certain  known  conditions,  it  is  well  to  notice  the  position 
of  the  index  pointer  N,  in  order  to  be  able  at  once  to 
adjust  it  to  about  the  right  point  on  other  occasions. 
Under  ordinary  circumstances,  during  daylight  it  is  best 
to  set  the  gas  nearly  full  on  at  first,  and  fully  on  at  about 
five  minutes  afterwards  when  the  draught  has  become  more 
powerful;  but  during  twilight,  when  the  supply  of  gas 
from  the  gas  works  is  more  free,  the  index  pointer  may  be 
set  at  the  numbers  2^  or  3.  The  gas  should  be  supplied 
by  a  pipe  of  not  less  than  §-inch  bore,  with  a  main  pipe  of 
1  an  inch  ;  but  all  depends  on  the  pressure  of  gas  at  the 
particular  locality,  which  is  very  variable.  The  consump- 
tion of  gas  varies  from  30  to  40  cubic  feet  per  hour,  the 
value  of  which  is  about  twopence. 

The  top  of  the  chimney  should  be  placed  in  a  position 
where  the  products  of  combustion  can  pass  freely  away. 
If  it  is  placed  in  an  opening  or  pipe  leading  to  another 
chimney,  care  must  be  taken  not  to  have  the  draught  too 
powerful,  otherwise  the  heat  will  be  drawn  more  into  the 
chimney,  and  the  supply  of  gas  in  the  daytime  may  be 
found  rather  deficient.  The  furnace  will  act  satisfactorily 
though  less  powerfully,  with  the  chimney  standing  in  an 
open  room  without  any  special  outlet  for  the  products  of 
combustion,  provided  the  full  height  (6  feet)  of  chimney  is 
employed.  Under  other  circumstances  a  chimney  4^  or  5 
feet  high  may  be  used. 

This  furnace  will  produce  what  is  generally  called  a 
white  heat ;  it  will  readily  melt  half  a  pound  of  copper,  or 


04  GORES   GAS   FURNACE. 

six  ounces  of  cast  iron  ;  it  will  melt  as  large  a  quantity  of 
those  substances  as  the  largest-sized  crucible  that  can  be  in- 
troduced into  it  will  contain,  sufficient  space  being  reserved 
around  the  crucible  for  draught.  It  requires  from  20  to  30 
minutes  to  acquire  its  highest  temperature,  and  then  the 
entrance  part  of  the  chimney  exhibits  a  faint  red  heat  in 
daylight.  If  it  exhibits  much  more  than  this,  the  draught 
is  too  powerful,  and,  if  less,  there  is  not  sufficient  gas. 

With  one  ounce  of  copper  put  into  the  cold  furnace, 
and  the  gas  lighted  and  properly  adjusted,  the  copper 
generally  begins  to  melt  at  about  the  tenth  or  twelfth 
minute,  and  is  completely  melted  by  the  fifteenth.  With 
the  heat  well  up,  1  ounce  of  copper  has  been  melted  in  it 
in  2J  minutes,  1  ounce  of  cast  iron  in  3  minutes,  5  ounces 
of  copper  in  4^  minutes,  and  3  ounces  of  cast  iron  in  5 
minutes.  With  the  smaller  hole  in  the  top  of  the  furnace 
open,  1  ounce  of  copper  has  been  melted  in  3],  minutes, 
and  several  ounces  of  copper  have  been  kept  in  fusion 
for  upwards  of  half  an  hour,  and  may  be  kept  so  for  any 
length  of  time  ;  cast  iron  has  also  been  fused  and  kept 
melted  under  the  same  conditions.  These  various  effects 
have  also  been  obtained  in  a  somewhat  diminished  degree 
with  the  chimney  standing  in  an  open  room. 

When  the  small  hole  D  is  open  some  air  is  drawn  in 
that  way,  and  less  air  passes  up  with  the  gas  through  the 
tube  0,  but  the  cold  air  does  not  much  diminish  the 
temperature  of  the  crucible,  because  it  combines  with  the 
•excess  of  gas  now  passing  over  the  edge  of  the  inner 
cylinder  ;  it,  however,  renders  the  flame  round  the  crucible 
white  by  deficiency  of  air,  and  this  should  be  partly  cor- 
rected by  lessening  the  gas.  An  excess  of  either  gas  or 
air  renders  the  surface  of  melted  copper  dull. 

When  it  is  desirable  to  perfectly  avoid  contact  of  air 
with  the  fused  substance  during  manipulation,  a  narrow 
crucible  should  be  employed,  and  a  thin  narrow  ring  of 
fire-clay  should  be  placed  upon  the  top  of  the  tube  0  to 
contract  its  opening  ;  the  flame  then  closes  completely 
over  the  top  of  the  crucible  and  prevents  access  of  air  ; 
a  proper  adjustment  of  gas,  together  with  exclusion  of  air 


REVERBERATORY  GAS  FURNACE.  95 

in  this  manner,  enables  a  perfectly  bright  surface  of 
melted  copper  or  even  tin  to  be  continuously  maintained 
from  which  the  images  of  parts  above  are  clearly  reflected. 
The  clay  ring  may  be  withdrawn  by  lifting  the  plate  B. 
A  less  perfect  exclusion  of  air  may  be  obtained  by  em- 
ploying a  narrow  crucible  placed  rather  low  down  in  its 
support.  A  small  iron  dish  should  be  placed  beneath  the 
tube  Z,  to  receive  any  melted  substance  that  may  fall. 
The  chief  conditions  of  success  in  the  use  of  this  furnace 
are  sufficient  gas,  a  suitable  degree  of  draught,  and  proper 
regulation  of  gas  to  air. 

Mr.  Griffin  has  devised  what  he  calls  a  Reverberatory 
Gas  Furnace,  which  also  produces  a  high  temperature 
without  the  use  of  a  blowing-machine.  It  is  especially 
suitable  for  assay  purposes  on  a  small  scale,  and  for  the 
decomposition  of  siliceous  minerals  by  fusion  with  alkaline 
-carbonates  in  platinum  crucibles,  being  capable  of  fusing 
1,000  grains  of  anhydrous  sodium  carbonate  in  ten  minutes. 

The  different  parts  of  this  furnace  are  also  arranged  in 
a  very  convenient  manner,  so  as  to  admit  of  its  being 
employed  for  various  purposes  in  a  chemical  or  assay  labo- 
ratory. It  is  based  upon  a  new  form  of  gas-burner  which, 
aided  by  suitable  bellows,  can  be  used  as  a  convenient 
source  of  heat  for  most  operations  of  the  chemical  laboratory 
and  lecture  table.  It  will  boil  a  quantity  of  liquid,  exceed- 
ing two  gallons,  at  once  ;  it  will  raise  a  4£-inch  fire-clay 
crucible  to  full  redness  ;  it  will  fuse  anhydrous  sodium  car- 
bonate in  greater  quantity  than  is  required  for  the  analysis 
of  a  siliceous  mineral;  and  it  will  melt  small  quantities 
of  sterling  silver.  This  amount  of  power  is  sufficient  for 
most  chemical  and  many  metallurgical  operations. 

Fig.  47  represents  the  gas-burner  of  this  apparatus. 
The  gas  is  supplied  by  the  horizontal  tube,  whence  it 
passes  through  a  set  of  small  holes  into  the  box  a,  in 
which  it  mixes  with  atmospheric  air  that  enters  freely  by 
the  holes  shown  in  the  sketch.  The  gaseous  mixture 
passes  up  the  vertical  tube  b,  and  is  inflamed  at  the  top, 
where  it  burns  with  a  single  tall  blue  flame,  which  gives 
no  smoke,  very  little  light,  but  much  heat.  In  this 


96 


REVERBERATORY   GAS   FURNACE. 


condition  the  apparatus  differs  from  'Bunsen's  gas-burner* 
only  in  size,  c  represents  a  thin  brass  cap,  which  fits  the 
air-box  a,  but  moves  easily  round  it ;  d  is  a  flat  cast-iron 
box  with  many  holes  around  the  margin,  and  a  few  small 
ones  on  the  top.  This  box  fits  loosely  on  the  upper  part 
of  the  tube  b,  and  when  it  is  placed  on  it  and  the  gas  is 
lighted  the  flame  produced  consists  of  a  series  of  radiating 
jets,  forming  a  horizontal  circular  flame  of  about  seven 
inches  in  diameter.  Fig.  48  shows  a  ring  of  horizontal 
flame  produced  ;  47  b  gives  a  single  vertical  flame.*  The 
ring  of  flame  is  suited  to  the  purposes  of  boiling  and 
evaporation ;  the  single  flame,  to  ignition  and  fusion. 
The  height  of  the  apparatus  represented  by  fig.  47  is 
twelve  inches ;  the  bore  of  the  tube  b  is  one  inch ;  and 
the  diameter  of  the  fire-box  d  is  four  inches. 

When  a  large  crucible  is  to  be  heated  to  redness,  the 
gas-burner  is  to  be  used  without  the  rose,  and  is  to  be 
arranged  with  the  furnace  fittings  that  are  represented  in 
perspective  by  fig.  49,  and  in  section  by  fig.  50,  and  the 
lower  part  of  fig.  51,  a,  b,  c,  d.  Letter  a  represents  the 
gas-burner ;  fig.  49  b  is  a  tall  iron  stool ;  c  a  chimney 
which  collects  atmospheric  air  toTeed  the  flame,  and  leads 
it  up  close  to  the  vertical  tube  of  a,  by  which  contrivance 
the  air  is  warmed  and  the  tube  cooled  ;  d  is  a  furnace-sole 

or  plate  of  fire-clay ; 
/  is  a  reverberatory 
dome,  the  interior  of 
which  is  best  shown 
in  the  section  fig.  50  ; 


FIG.  47. 


FIG.  48. 


e  is  a  cast-iron  ring 
or  trivet,  represented 
more  clearly  in  fig. 
52  ;  g  is  an  iron  chim- 
ney 24  inches  long 
and  3|  inches  wide ;  and  h  a  damper  to  lessen  the  draught 
when  small  crucibles  are  to  be  heated.  The  height  of 

*  Fig.  48  represents  a  small  variety  of  this  gas-burner,  in  which  the  head 
is  not  removable,  but  the  efflux  of  the  mixed  gases  is  regulated  by  a  sliding- 
valve,  which  is  represented  by  b. 


REVERBERATORY  GAS  FURXACE. 


97 


this  apparatus  from  a  to  the  top  of /is  24  inches  ;  and 
the  external  diameter  of  the  dome  /  is  about  8  inches. 
The  crucible,  which  may  be  from  4^  to  4|  inches  in 


FIG.  49. 


FIG.  50. 


FIG.  52. 


height,  is  placed  on  the  iron  ring  0,  fig.  51,  and  that  on 
the  clay  sole  d,  and  it  is  then  covered  by  the  dome/. 
The  gas  should  be  lighted  after  the  crucible  is  placed  in 
its  position  and  before  the  dome  is  put  on.  The  dome 


98  REVERBERATOKY  GAS  FURNACE. 

and  the  chimney  are  then  to  be  added  and  the  operation 
allowed  to  proceed.  With  a  crucible  of  the  above  size 
the  damper  h  is  not  required  ;  but  it  must  be  used  when 
the  crucible  is  under  4  inches  in  height,  otherwise  the 
draught  occasioned  by  extra  space  within  the  dome  causes 
the  flame  to  blow  down.  The  damper  must  be  put  on  the 
chimney  before  the  chimney  is  put  on  the  dome.  The 
iron  ring  (fig.  52  or  e  fig.  51)  suits  crucibles  of  different 
sizes,  according  to  which  side  of  it  is  turned  uppermost. 

The  figures  show  that  a  crucible  mounted  in  this 
furnace  can  lose  very  little  heat  by  radiation  or  conduc- 
tion, and  hence  it  is  that  a  small  gas  flame  produces  a 
powerful  effect.  In  half  an  hour  a  4|-inch  clay  crucible, 
filled  and  covered,  can  be  heated  to  full  redness.  The 
progress  of  the  ignition  can  be  easily  examined  by  lifting 
up  the  chimney  g  and  the  dome  /  by  their  respective 
wooden  handles.  But  the  action  of  the  furnace  can  also 
be  judged  of  by  a  peculiar  roaring  noise  which  it  pro- 
duces. If  the  gas  and  air  are  mixed  in  due  proportions, 
the  roar  is  regular  and  continuous ;  if  there  is  too  much 
gas  the  roar  is  lessened,  if  too  much  air  the  roar  is 
increased,  but  is  rendered  irregular  and  intermittent. 
The  greater  the  noise,  the  greater  the  heat  in  the  furnace. 
And  when  the  roar  becomes  spasmodic  the  flame  is  on  the 
point  of  blowing  down.  To  prevent  that  occurrence,  the 
proportion  of  air  must  be  lessened  or  that  of  gas  increased. 

The  following  arrangement  is  convenient  when  small 
crucibles  are  to  be  strongly  heated  :  anhydrous  carbonate 
of  soda  in  quantities  exceeding  1,000  grains  can  be  thus 
readily  fused  in  a  platinum  crucible,  and  sterling  silver  can 
be  melted  in  a  clay  crucible.  It  is  also  available  for  igni- 
tions or  fusions  in  small  porcelain  crucibles.  Fig.  50  re- 
presents the  arrangement  of  apparatus,  as  seen  in  section  : 
a  is  the  gas-burner  ;  b  the  stool ;  c  the  air  chimney,  and  d 
the  furnace-sole,  as  already  explained  ;  i  is  a  cylinder  of 
fire-clay,  4  inches  high,  and  4|  inches  diameter  ;  Jc  is  a 
fire-clay  furnace,  in  which  is  placed  a  small  cast-iron  ring 
about  2  inches  in  diameter,  similar  in  form  to  that  repre- 
sented by  fig.  52,  and  on  this  ring  the  platinum  crucible  is 


PRINCIPLES    OF   HEATLYG   BY   GAS. 


99 


FIG.  53. 


adjusted  ;  /  is  a  fire-clay  or  plumbago  reverberatory  dome  ; 
and  g  is  the  chimney  that  forms  part  of  the  furnace  repre- 
sented by  fig  48.  The  crucible  being  adjusted,  the  gas 
lighted,  and  the  dome  and  chimney  put  on,  the  lapse  of 
twelve  or  fifteen  minutes,  according  to  the  quality  and 
pressure  of  the  gas,  suffices  for  the  fusion  of  1,000  grains 
of  carbonate  of  soda  in  a  platinum  crucible.  At  the  heat 
which  this  furnace  produces,  the  cast-iron  ring  does  not 
melt  nor  alloy  with  the  platinum  crucible  placed  upon  it. 
By  a  modification  of  these  arrangements,  Mr.  Griffin 
has  made  a  gas  furnace  for  melting  quantities  of  lead,  zinc, 
antimony,  &c.  This  is  represented  by  fig.  53.  The  iron 
crucible  will  contain  nearly  30  Ibs. 
of  lead  and  about  24  Ibs.  of  zinc. 
The  burner  readily  melts  these  quan- 
tities, and  then,  with  a  diminished 
quantity  of  gas,  will  keep  the  metals 
fluid.  The  metals  being  protected 
from  the  air  suffer  li ttle  loss  by  oxida- 
tion. Such  operations  as  the  granula- 
tion of  zinc  are  performed  with  this 
apparatus  with  great  facility ;  it  serves 
also  for  baths  of  fused  metal.  In  a 
large  furnace  of  this  kind,  made  for 
a  special  operation,  60  Ibs.  of  zinc 
have  been  melted  with  ease,  and 
the  inventor  believes  that,  used  in 
this  manner,  the  burner  is  powerful 
enough  to  melt  a  hundredweight  of 


zinc. 


The  principles  of  heating  by  gas, 
which  have  led  Mr.  Griffin  to  the  construction  of  these 
gas  furnaces,  may  be  summed  up  as  follows:  When  a 
crucible  or  other  solid  body  is  to  be  heated,  it  is  to  be 
wrapped  in  a  single  flame  at  the  point  of  maximum  heat, 
and  loss  of  heat  by  radiation  and  conduction  is  to  be  pre- 
vented by  the  interposition  of  non-conducting  materials 
(plumbago  or  fire-clay) ;  and  when  liquids  are  to  be  boiled 
or  evaporated,  particularly  when  they  are  contained  in 


H  2 


100  BUNSEN  S   GAS    BURNER. 

vessels  of  glass  or  porcelain,  the  flame  is  to  be  broken  up 
into  numerous  horizontal  jets,  and  these  are  to  be  made 
to  supply  a  large  and  regular  current  of  highly  heated 
air,  by  which  alone,  and  not  by  the  direct  application  of 
the  flame,  the  vessel  that  contains  the  liquid  is  to  be  heated. 
In  both  cases  provision  must  be  made  to  secure  a  sufficient 
draught  of  air  through  the  furnace,  because  every  cubic 
foot  of  gas  requires  for  combustion  10  or  12  cubic  feet  of 
air,  and  the  gases  which  have  done  their  duty  must  be 
rapidly  carried  away  from  the  focus  of  heat.  If  the  steam, 
the  carbonic  acid  gas,  and  the  free  nitrogen  which  consti- 
tute the  used-up  gases  are  not  promptly  expelled,  fresh 
gaseous  mixture  in  the  act  of  producing  additional  heat 
by  combustion  cannot  get  near  the  object  that  is  to  be 
heated,  and  the  heat  so  produced  out  of  place  is  wasted. 

Bunsen's  gas-burner,  whatever  its  size,  is  subject  to 
two  defects  :  sometimes  the  flame  burns  white  and  smoky, 
and  sometimes  it  blows  down,  the  gaseous  mixture  ex- 
plodes, and  the  gas  then  burns  with  a  smoky  flame  in  the 
tube.  The  remedies  for  these  defects  are  as  follows  :  If 
the  flame  is  white  only  when  the  gas  is  turned  on  very 
full,  the  remedy  is  to  lessen  the  supply  of  gas  ;  but  if  the 
flame  continues  to  burn  white  at  the  top  when  the  gas  is 
gradually  turned  off  and  the  mass  of  flame  slowly  sinks, 
then  the  holes  which  deliver  the  gas  from  the  supply  pipe 
into  the  air-box  a  (fig.  47)  are  too  large,  and  are  placed 
too  directly  under  the  centre  of  the  vertical  tube  b  (fig.  47), 
and  these  defects  must  be  corrected  in  the  instrument. 
Finally,  when  the  flame  blows  down,  it  is  because  the 
supply  of  atmospheric  air  is  too  large  in  proportion  to  the 
supply  of  gas,  and  their  relative  proportions  must  be 
altered.  To  effect  this  alteration  the  cap  c  is  to  be  turned 
round  on  the  air-box  a  so  as  partially  to  close  the  holes, 
and  thus  lessen  the  supply  of  air.  If,  when  the  gas  is 
alight,  the  flame  needs  to  be  lowered,  first  the  supply  of 
air  is  to  be  lessened  and  then  the  supply  of  gas.  If  the 
flame  is  to  be  enlarged,  first  the  supply  of  gas  must  be 
increased  and  then  the  supply  of  air.  In  short,  to  prevent 
the  flame  blowing  down,  the  gas  must  always  be  placed  in 


BUXSEN  S   GAS-BUKNER.  1C1 

excess,  and  then  have  the  proper  quantity  of  air  adjusted 
to  suit  it  by  means  of  the  regulator  c.  When  gas-burners 
of  this  description  have  to  be  used  in  a  locality  where  the 
pressure  of  the  gas  is  slight,  especially  in  the  daytime, 
there  is  a  constant  tendency  in  the  flame  to  blow  down. 
The  best  way  to  prevent  that  occurrence  is  to  supply  the 
gas  by  a  pretty  wide  tube,  and  to  see  that  the  current  of 
gas  is  not  checked  by  a  very  narrow  bore  in  the  plug  of 
an  intervening  stop-cock,  which  is  often  the  unsuspected 
cause  of  want  of  pressure  in  the  supply  of  gas.  If  this 
does  not  suffice  to  prevent  the  blowing  down  of  the  gas, 
the  holes  which  admit  the  gas  from  the  supply  pipe  into 
the  box  a  of  the  burner  should  be  enlarged,  more  or  less 
according  to  necessity.  A  large  supply  of  gas  compen- 
sates, to  some  extent,  for  want  of  pressure. 

When  a  steady  and  long-continued  heat  is  desired  from 
a  Bunsen's  burner,  it  is  proper  to  use  tw~o  stop-cocks  and 
a  length  of  caoutchouc  tube  between  them.  One  of  these 
stop-cocks  is  to  be  affixed  to  the  burner,  and  the  other  to 
the  supply  pipe.  The  latter  is  to  be  opened  wider  than  is 
necessary  to  supply  the  required  quantity  of  gas,  and  the 
former  is  to  be  used  to  regulate  the  supply  to  the  burner 
exactly ;  under  these  circumstances,  if  another  stop-cock 
is  opened  and  gas  burnt  in  the  immediate  neighbourhood, 
the  flame  does  not  so  readily  blow  down  in  the  regulated 
burner  as  it  does  when  only  the  stop-cock  on  the  supply 
pipe  is  used. 

When  a  crucible  is  suspended  by  wires  or  by  a  ring 
over  the  flame  of  a  spirit  lamp  or  gas-burner,  the  flame 
and  the  hot  air  supplied  by  the  flame  strike  the  crucible 
for  an  instant  and  then  pass  away  to  do  no  more  good. 
At  the  same  time,  the  effect  of  the  heating  power  on  the 
crucible  is  lessened  by  other  circumstances  ;  namely,  by 
radiation  on  all  sides,  by  a  mass  of  cold  air  which  con- 
stantly rises  around  and  in  contact  with  it,  and  by  the  con- 
ducting power  of  the  metallic  apparatus  which  supports 
both  the  crucible  and  the  lamp.  These  losses  are  avoided 
if  the  crucible  is  inclosed  in  a  furnace  made  of  a  non- 
conducting material,  such  as  fire-clay,  which  can  absorb 


102  METHOD    OF   MOUNTING   CRUCIBLES. 

and  retain  heat.  In  the  descriptions  of  the  gas  furnaces, 
and  in  that  of  Mr.  Charles  Griffin's  oil-lamp  furnace,  several 
methods  of  mounting  crucibles  in  fire-clay  jackets  have 
been  shown  ;  and  we  will  now  describe  some  of  Mr.  Griffin's 
fittings  that  may  be  used  to  construct  temporary  table  fur- 
naces for  crucibles  that  are  to  be  exposed  to  the  flame 
produced  by  gas,  oils,  or  spirit  up  to  a  temperature  close 
upon,  but  not  quite  up  to,  a  white  heat ;  that  is  to  say, 
up  to  a  heat  that  will  readily  melt  anhydrous  carbonate  of 
soda  and  small  quantities  of  silver,  and  so  be  fit  for  many 
metallurgical  operations,  but  which  will  not  melt  copper 
nor  cast  iron. 

Fig.  54  represents  sections  of  cylinders  of  fire-clay 
which  are  drawn  on  a  scale  of  1  to  8,  and  have  the  rela- 
tive heights  and  bores  represented  in  the  figures.  The 
clay  pieces,  that  is  to  say,  as  many  of  them  as  are  necessary 
for  a  given  purpose,  can  be  adjusted  over  a  gas-flame  by 
means  of  a  tripod  (fig.  49)  or  a  clay  support. 

The  crucible  to  be  operated  upon  is  to  be  supported  on 
a  toothed  ring  made  either  of  cast  iron  or  fire-clay,  such 
as  are  represented  by  figs.  52  and  55.  Fig.  52  is  a  ring 
of  cast  iron,  h  representing  it  in  section  and  i  as  seen  from 
above.  It  is  about  two  inches  in  diameter,  and  has  three 
teeth  projecting  towards  the  middle  of  the  ring.  This 
ring  can  be  supported  by  any  of  the  clay  cylinders  whose 
bore  does  not  exceed  two  inches.  Fig.  55  is  a  ring  of 
fire-clay  of  4  inches  external  diameter,  and  1  inch  in  thick- 
ness, provided  with  three  teeth  that  project  inwards,  and 
upon  which  a  crucible  can  be  supported  without  injuring 
the  draught  of  the  gas  furnace. 

Both  these  grates  will  support  crucibles  at  the  highest 
temperature  which  can  be  produced  by  spirit,  oil,  or  gas, 
without  a  blast  of  air  ;  but  at  a  white  heat  produced  by  any 
of  these  fuels  with  a  blast  of  air,  the  iron  ring  melts,  and, 
if  the  heat  is  long  continued,  those  of  fire-clay  soften  and 
partially  give  way.  When  the  fire-clay  grate  (fig.  55)  is 
required  to  sustain  a  very  high  temperature  for  a  consider- 
able time,  it  is  proper  to  have  it  made  of  6  inches  diameter, 
as  represented  by  fig.  54  p^  the  air-way  in  which  is  the 


MOUNTS   FOR   CRUCIBLES. 


103 


same  as  that  of  the  small^  grate,  but  the  clay  ring  is  much 
stronger. 

The    grate    is    fixed  FlG- 54- 

above  the  flame  at  a  dis- 
tance which  is  found  by 
trial  to  place  the  crucible 
on  the  point  of  great- 
est heat.  Commonly  a 
4-inch  cylinder  (54,  h  or 
(/)  placed  upon  a  suitable 
support  serves  the  pur- 
pose. The  bore  of  the 
cylinders  at  the  bottom 
must  be  wider  than  the 
burner,  to  allow  of  a 
considerable  influx  of 
atmospheric  air  around 
the  flame.  The  grate  is 
placed  on  this  cylinder, 
the  crucible  on  the  grate, 
and  then  another  cylin- 
der around  the  crucible. 
The  choice  of  this  upper 
cylinder  depends  entirely 
upon  the  size  of  the  cru- 
cible that  is  to  be  heated. 
Whatever  the  size  of 
the  crucible,  the  cylinder 
must  be  so  chosen  as  to  fit  the  crucible  as  accurately  as 
possible,  leaving  between  it  and  the  furnace  walls  an  open 
space  of  not  less  than  -|  inch,  nor  more  than 
^  inch  all  round.  If  the  upper  cy Under  is 
not  contracted  at  top  like  54  e  f  g,  then 
a  cylinder  of  narrow  bore,  such  as  54  a 
or  c,  must  be  put  upon  it,  in  order  to  de- 
flect the  flame  and  the  rising  current  of 
hot  air  upon  the  top  of  the  crucible,  and  * 

thus  produce  a  reverberatory  furnace.     Finally,  an  iron 
chimney,  2  or  3  feet  long,  must  be  put-  upon  the  fur- 


FIG.  55. 


104  MOUNTS   FOR   CRUCIBLES. 

nace,  to   force    up    a   draught    of  air   sufficient  to  feed 
the  flame. 

Suppose  a  small  rose  gas-burner  is  to  be  arranged  for 
an  ignition,  with  the  use  of  a  fire-clay  support,  the  com- 
bination of  pieces  necessary  for  the  purpose  may  be  those 
represented  by  fig.  56,  where  A  is  the  fire-clay  support, 
and  the  rest  of  the  pieces  are  those  which  are  shown  at 
fig,  54,  and  described  at  the  letters  placed  against  each  of 
them  in  this  figure.  It  is  evident  that  the  application  of 
this  furnace  to  crucibles  of  different  sizes 'depends  upon 
the  proper  choice  of  the  cylinders  here  marked  i  and  e. 
Of  course  there  is  only  a  limited  choice  of  crucibles  suit- 
able for  such  operations.  Three  inches  is  the  extreme 
width  between  the  furnace  walls  of  any  of  the  pieces  in 
fig.  54,  from  a  to  </,  and  though  larger  cylinders  could  be 
used,  such  as  i  to  0,  it  must  be  remembered  that  the  flame 
of  a  lamp  without  blast  has  only  a  limited  power,  and  that 
although  a  given  flame  will  fuse  1,000  grains  of  carbonate 
of  soda  in  a  platinum  crucible,  it  may  only  heat  to  a 
moderate  redness  a  large  clay  crucible.  Yet,  considering 
that  low  degrees  of  heat  are  suitable  for  many  purposes,  it 
is  convenient  to  have  the  power  of  readily  adjusting  a 
temporary  furnace  to  the  bulk  of  any  crucible  which  it  is 
desired  to  heat. 

The  clay  pieces  (fig.  54  i  to  p)  are  those  that  have  been 
expressly  designed  for  the  blast  oil  furnace  already  de- 
scribed ;  but  these  can  also  be  used  for  spirit  and  gas  fur- 
naces, the  respective  sizes  being  chosen  in  each  case  ac- 
cording to  the  size  of  the  crucible  that  is  to  be  ignited. 

In  respect  to  the  means  of  supporting  a  crucible,  it  has 
been  shown  that  clay  trivets  with  a  wide  flange,  namely, 
the  6-inch  trivets  fig.  54  p,  will  support  a  crucible  contain- 
ing 5  Ibs.  of  iron  until  that  quantity  of  iron  is  melted,  even 
under  the  operations  of  a  blast ;  so  that  it  is  evident  that 
this  method  of  supporting  a  crucible  in  a  gas  flame  may 
be  always  depended  upon  when  no  blowing-machine  is 
employed. 

Fig.  57  represents  the  gas  furnace  arranged  for  boiling 
or  evaporating :  a  is  the  gas-burner  ;  b  an  iron  stool  with 


TEMPORARY   GAS   FURNACES. 


105 


three  legs  ;  c  a  furnace  body  or  iron  jacket  lined  with 
plumbago  or  fire-clay.  This  furnace  may  be  14  inches 
high  and  9  inches  in  diameter.  The  three  brackets  fixed 
on  the  upper  part  of  the  jacket  serve  to  support  the  vessel 
that  contains  the^liquid  that  is  to  be  boiled  or  evaporated. 
A  porcelain  basin  of  16  or  18  inches  in  diameter  can  be 
thus  supported.  It  is  important  to  allow  between  the 
jacket  c  and  the  evaporating  basin  plenty  of  space  for  the 
escape  of  the  heated  air,  which  ascends  from  the  interior 


FIG.  56. 


FIG.  57. 


of  the  furnace.  When  the  evapo- 
rating basin  is  of  small  diameter,  it 
may  be  supported  on  iron  triangles, 
placed  in  the  furnace  c.  The  section 
shows  that  around  the  vertical  tube 
of  the  gas-burner  a  there  is  in  the 
bottom  of  the  furnace  c  a  circular 
opening  which  is  of  2  inches  diame- 
ter, and  through  which  air  passes  freely,  partly  to  feed  the 
flame  and  partly  to  be  heated  by  the  flame  and  be  directed 
upwards  in  a  continuous  current  upon  the  lower  surface 
of  the  basin  that  is  to  be  heated.  The  flame  within  the 
furnace  burns  steadily.  No  side  currents  of  air  agitate  it. 
No  part  of  it  touches  the  basin,  which  should  receive  its 
heat  solely  from  the  mass  of  ascending  hot  air.  The  gas- 
burner  thus  arranged  and  supplied  by  a  gas-pipe  of  ^-inch 
bore,  burns  about  3  cubic  feet  of  gas  in  an  hour,  and  the 
flame  which  it  produces,  acting  upon  water  contained  in 


106  SOLID -FLAME   BURNER. 

an  open  porcelain  evaporating  basin,  will  heat  from  60° 
to  212°  P.— 

1  quart  in       5  minutes 

1  gallon  in    15       „ 

2  gallons  in  30      „ 

and  when  the  water  boils  it  is  driven  off  in  steam  at  the 
rate  of  more  than  a  gallon  of  water  per  hour.  The  method 
is  consequently  applicable  to  distillation  on  a  small  scale, 
and  to  numerous  other  laboratory  operations. 

An  excellent  gas-burner  for  general  laboratory  use  is 
Mr.  Fletcher's  solid-flame  burner,  shown  in  fig.  58.  This 
is  one  of  the  very  best  heating  burners  which  has  yet  been 
made.  The  flame  is  of  a  brilliant  green  colour,  solid,  and 

FIG.  58. 


of  the  same  temperature  throughout ;  the,  usual  heating 
burners  having  a  flame  with  a  hollow  centre  of  uncon- 
sumed  gas.  The  pattern  shown  in  the  figure  measures 
only  3^  inches  in  height,  and  it  will  melt  half  a  hundred- 
weight of  lead  in  an  iron  pot.  It  will  boil  half  a  gallon  of 
water  in  a  flat  copper  kettle  in  five  minutes,  and  will  melt 
6  Ibs.  of  lead  or  solder  in  an  iron  ladle  in  seven  minutes. 
The  burner  can  be  adapted  for  a  blast  where  very  high 
power  is  required  in  a  small  burner.  With  a  blast  it  can 
be  made  to  consume  any  gas  supply  up  to  200  cubic  feet 
per  hour,  giving  a  very  high  duty.  One  advantage  which 
this  burner  possesses  over  those  of  the  ordinary  kind  with 
wire-gauze  tops,  is  that  it  cannot  be  spoiled  by  any  acci- 
dent. In  case  a  solution  boils  over,  and  chokes  the  holes 


LUTES   AND    CEMENTS.  107 

in  the  perforated  copper  dome,  the  latter  can  be  lifted  off 
(when  the  burner  is  warm)  and  cleaned.  The  whole 
burner  is  designed  to  stand  the  roughest  and  heaviest 
work  without  injury. 

A  smaller  size  of  this  burner,  of  little  less  than  half 
the  power,  is  shown  in  fig.  59. 

The  india-rubber  tubing  for  these  burners  must  be  of 
good  size,  and  smooth  inside,  made  without  wire. 

FIG.  59.  FIG.  60. 


The  burner  shown  in  fig.  60  is  a  very  excellent  evapo- 
rating burner  for  glass  and  porcelain  vessels  and  general 
laboratory  work.  It  is  a  great  improvement  on  the  ordin- 
ary coil  burners  in  use,  owing  to  the  fact  that  no  currents 
of  cold  air,  which  are  so  fatal  to  glass  and  porcelain 
dishes,  can  reach  the  vessel,  as  is  the  case  with  all  coil 
burners.  The  flames  are  blue  and  smokeless,  and  are  not 
liable  to  be  extinguished  with  a  splash,  being  raised  above 
the  body  of  the  burner.  Vessels  must  not  be  put  in  con- 
tact with  the  flame  ;  half  the  diameter  of  the  burner  must 
be  taken  as  the  nearest  distance  at  which  a  vessel  can  be 
placed  above  the  top  of  the  burner. 

LUTES   AND    CEMENTS. 

It  may  be  as  well  to  mention  in  this  part  of  the  work 
the  various  lutes  and  cements  which  may  be  employed, 
either  in  fire  operations  or  in  making  good  joints  in 
experiments  with  gases  or  liquids.  The  following  are  the 
principal  kinds. 

FIEE  LUTE  is  composed  of  good  clay  two  parts,  sharp 
washed  sand  eight  parts,  horse-dung  one  part.  These 


108  LUTES  AND    CEMENTS. 

materials  are  to  be  intimately  mixed  ;  and  afterwards  the 
whole  is  to  be  thoroughly  tempered  like  mortar.  Mr. 
Watt's  fire  lute  is  an  excellent  one,  but  is  more  expensive. 
It  is  made  of  finely  powdered  Cornish  (porcelain)  clay 
mixed  to  the  consistence  of  thick  paint,  with  a  solution 
of  borax  in  the  proportion  of  2  ounces  of  borax  to  a  pint 
of  hot  water. 

FAT  LUTE  is  prepared  by  mixing  fine  clay,  in  a  fine 
powder,  with  drying  oil,  so  that  the  mixture  may  form  a 
ductile  paste.  When  this  paste  is  used,  the  part  to  which 
it  is  applied  ought  to  be  very  clean  and  dry,  otherwise  it 
will  not  adhere.  Glazier's  putty  is  very  similar  to  this. 

KOMAN  CEMENT. — This  must  be  kept  in  well-closed 
vessels,  and  not  moistened  until  it  is  required  for  use. 

PLASTER  OF  PARIS. — This  is  mixed  with  water,  milk,  or 
weak  glue,  or  starch  water. 

These  three  lutes  stand  a  dull  red  heat :  the  two  latter 
may  be  rendered  perfectly  impermeable  to  gaseous  bodies 
by  being  .smeared  over  with  oil,  or  a  mixture  of  oil  and 
wax. 

LINSEED  OR  ALMOND  MEAL,  mixed  to  the  consistence  of  a 
paste  with  water,  milk,  lime  water,  or  starch  paste.  This 
lute  is  very  manageable  and  impermeable,  but  does  not 
withstand  a  heat  greater  than  about  500°  F. 

LIME  AND  EGG  LUTE. — If  just  the  sufficient  quantity  of 
water  be  added  to  quick  lime  to  reduce  it  to  a  dry  powder, 
and  that  is  mixed  well  and  rapidly  with  white  of  egg 
diluted  with  its  own  volume  of  water,  and  the  mixture 
spread  immediately  on  strips  of  linen  and  applied  to  the 
part,  then  powdered  with  quick  lime,  it  forms  a  good 
cement.  Instead  of  white  of  egg,  lime  and  cheese  may 
be  used,  or  lime  with  weak  glue  water.  This  lute  dries 
very  rapidly,  becoming  very  hard  and  adhering  strongly 
to  glass  ;  but  its  great  inconvenience  is  the  want  of 
flexibility. 

WHITE  LEAD  MIXED  WITH  OIL — If  this  mixture  be  spread 
upon  strips  of  linen,  or  bundles  of  tow,  it  acts  much  in  the 
same  manner  as  the  lime  lutes. 

YELLOW  WAX  is  often  used  as  a  lute,  but  it  becomes 


LUTES  AND   CEMENTS.  109 

very  brittle  at  a  low  temperature.  It  may  be  rendered 
less  brittle,  and  at  the  same  time  more  fusible,  by  an 
admixture  of  one  eighth  crude  turpentine. 

SOFT  CEMENT  is  prepared  by  fusing  yellow  wax  with 
half  its  weight  of  crude  turpentine  and  a  little  Venetian 
red  in  order  to  colour  it.  It  is  very  flexible,  and  takes 
any  desired  form  under  the  pressure  of  the  fingers. 

WATERPROOF  CEMENT. — Mr.  Edmund  Davy,  P.E.S.,  de- 
scribed a  cement  made  by  melting  in  a  saucepan  two 
parts  by  weight  of  common  pitch,  and  adding  to  it  one 
part  by  weight  of  gutta-percha,  stirring  and  mixing  them 
well  together  until  they  were  completely  incorporated 
with  or  united  with  each  other.  The  mixture  then  forms 
a  homogeneous  fluid  which  may  be  used  in  this  state  for 
many  purposes,  and  is  remarkable  on  account  of-  the 
facility  and  tenacity  with  which  it  adheres  to  metals, 
stones,  and  glass.  It  may  be  poured  into  a  large  basin  of 
cold  water,  in  a  thinner  or  thicker  stream,  or  as  a  cake. 
In  this  state,  while  warm,  it  is  quite  soft,  but  may  be  soon 
taken  up  out  of  the  water  and  drawn  out  into  longer  or 
pressed  into  shorter  pieces,  or  cut  or  twisted  into  frag- 
ments, which  may  again  be  readily  reunited  by  pressure. 
When  the  cement  is  cold,  or  before,  it  may  be  removed 
from  the  water  and  wiped  dry,  when  it  is  fit  for  use.  It 
is  of  a  black  colour  ;  when  cold,  it  is  hard.  It  is  not 
brittle,  but  has  some  degree  of  elasticity,  which  is  in- 
creased by  a  slight  increase  of  heat.  It  appears  to  be  not 
so  tough  as  gutta-percha,  but  more  elastic.  Its  tenacity 
is  very  considerable,  but  inferior  to  gutta-percha.  It 
softens  when  put  into  water  at  about  100°  F. ;  when 
heated  to  above  100°  F.  it  becomes  a  thin  fluid  :  and  if 
the  heat  is  gradually  increased  it  passes  through  inter- 
mediate stages  of  softness,  becomes  viscous  like  bird-lime, 
and  may  be  extended  into  threads  of  indefinite  length  :  it 
remains  in  this  state  even  when  exposed  for  some  time  in 
a  crucible  to  the  heat  of  boiling  water,  212°  F.  Water 
appears  to  have  no  other  action  upon  it  but  that  of  soften- 
ing it  when  warm  or  hot,  and  slowly  hardening  it  when 
cold.  The  cement  adheres  strongly,  if  pressed  on  metal 


110  LUTES   AND   CEMENTS. 

or  other  surfaces,  though  water  be  present,  provided  such 
surfaces  be  warm.  This  cement  is  applicable  to  many 
useful  purposes.  It  adheres  with  great  tenacity  to  metals, 
wood,  stones,  glass,  porcelain,  ivory,  leather,  parchment, 
paper,  hair,  feathers,  silk,  woollen,  cotton,  linen  fabrics, 
&c.  It  is  well  adapted  for  glazing  windows,  or  as  a 
cement  for  aquariums.  This  cement  does  not  appear  to 
affect  water,  and  it  will  apparently  be  found  applicable 
for  coating  metal  tanks ;  to  secure  the  joints  of  stone 
tanks  ;  to  make  a  glue  for  joining  wood,  which  will  not 
be  affected  by  damp ;  and  to  prevent  the  depredations  of 
insects  on  wood. 

KESINOUS  OR  HARD  CEMENT  is  made  by  fusing  together  at 
the  lowest  possible  temperature  one  part  of  yellow  wax 
and  five  or  six  of  resin,  and  then  adding  gradually  one  part 
of  red  ochre  or  finely  powdered  brickdust  (plaster  of  Paris 
succeeds  very  well),  and  then  raising  the  temperature  to 
212°  at  least,  until  no  more  froth  arises  or  agitation  takes 
place,  and  stirring  it  continually  until  cold.  This  cement 
is  employed  in  a  hot  state.  This  lute  is  much  used  for 
fixing  brass  caps,  &c.,  to  air-jars. 

CAOUTCHOUC. — Tubes  of  vulcanised  caoutchouc  form  a 
very  ready  means  of  attaching  one  piece  of  apparatus  to 
another,  and  they  possess  the  peculiar  advantage  of  flexi- 
bility, which  allows  the  various  parts  of  the  apparatus 
which  they  connect  to  move  in  different  directions  to 
a  slight  extent,  so  that  the  whole  is  not  so  likely  to 
be  fractured  as  when  connected  in  an  inflexible  manner. 
Caoutchouc  is  also  less  acted  upon  by  gases  and  vapours 
than  almost  any  other  substance  we  know  ;  even  chlorine 
attacks  it  but  slowly,  and  when  un vulcanised  it  possesses 
the  valuable  property  of  forming  a  perfect  joint  when 
freshly  cut  edges  are  brought  and  pressed  together,  hence 
the  facility  with  which  it  is  manufactured  into  tubes.  The 
mode  of  manufacturing  small  connecting  tubes,  which  are 
often  required  to  be  of  unvulcanised  caoutchouc,  is  as 
follows :  Take  a  piece  of  the  sheet  caoutchouc  of  the 
required  size,  and  warm  it  either  in  the  hand  or  before  a 
fire,  until  it  is  perfectly  soft ;  then  place  it  around  a  glass 


LUTES  AND   CEMENTS.  Ill 

rod  of  the  requisite  size,  pressing  the  edges  close  together 
with  the  fingers  ;  when  close  together  cut  off  the  super- 
abundance with  a  sharp  pair  of  scissors,  and  the  newly 
cut  edges  will  unite  by  simple  pressure  of  the  nail.  When 
well  executed  the  joint  is  scarcely  apparent.  In  order 
to  prevent  the  caoutchouc  from  adhering  to  the  rods  on 
which  the  tube  is  formed,  a  little  moisture  or  dry  starch 
may  be  employed.  When  caoutchouc  is  not  at  hand, 
oiled  paper  may  be  substituted,  the  joint  being  made  of 
wax. 

Faraday  gives  the  following  directions  for  luting  iron, 
glass,  or  earthenware  retorts,  tubes,  &c.,  for  furnace  opera- 
tions. When  the  lute  has  to  withstand  a  very  high  tem- 
perature it  should  be  made  of  the  best  Stourbridge  clay, 
which  is  to  be  made  into  a  paste  varying  in  thickness 
according  to  the  opinion  of  the  operator.  The  paste 
should  be  beaten  until  it  is  perfectly  ductile  and  uniform, 
and  a  portion  should  then  be  flattened  out  into  a  cake  of 
the  required  thickness,  and  of  such  a  size  as  shall  be  most 
manageable  with  the  vessel  to  be  coated.  If  the  vessel  be 
a  retort  or  flask,  it  should  be  placed  in  the  middle  of  the 
cake,  and  the  edges  of  the  latter  raised  on  all  sides  and 
gradually  moulded  and  applied  to  the  glass  ;  if  it  be  a 
tube  it  should  be  laid  on  one  edge  of  the  plate,  and  then 
applied  by  rolling  the  tube  forward.  In  all  cases  the 
surface  to  be  coated  should  be  rubbed  over  with  a  piece 
of  the  lute  dipped  in  -vyater  for  the  purpose  of  slightly 
moistening  and  leaving  a  little  of  the  earth  upon  it ;  if 
any  part  of  the  surface  becomes  dry  before  the  lute  is 
applied,  it  should  be  re-moistened.  The  lute  should  be 
pressed  and  rubbed  down  upon  the  glass  successively 
from  the  part  where  contact  was  first  made  to  the  edges, 
for  which  purpose  it  is  better  to  make  them  thin  by 
pressure  and  also  somewhat  irregular  in  form,  and  if 
at  all  dry  they  should  be  moistened  with  a  little  soft 
lute.  The  general  thickness  may  be  about  i  to  1  of  an 
inch. 

Being  thus  luted,  the  vessels  are  afterwards  to  be 
placed  in  a  warm  situation,  over  the  sand-bath  or  near 


112  LUTES   AND    CEMENTS. 

the  ash-pit,  or  in  the  sun's  rays.  They  should  not  be 
allowed  to  dry  rapidly  or  irregularly,  and  should  be 
moved  now  and  then  to  change  their  positions.  To  pre- 
vent cracking  during  desiccation,  and  the  consequent 
separation  of  the  coat  from  the  vessel,  some  chemists 
recommend  the  introduction  of  fibrous  substances  into 
the  lute,  so  as  mechanically  to  increase  the  tenacity  of  its 
parts.  Horse-dung,  chopped  hay  and  straw,  horse-  and 
cow-hair,  and  tow  cut  short,  are  amongst  the  number. 
When  these  -  are  used,  they  should  be  added  in  small 
quantity,  and  it  is  generally  necessary  to  add  more 
water  than  with  simple  lute,  and  employ  more  labour 
to  insure  a  uniform  mixture.  It  is  best  to  mix  the 
chopped  material  with  the  clay  before  the  water  is  put 
to  it,  and,  when  adding  the  latter,  to  mix  at  first  by 
stirring  up  the  mass  lightly  with  a  pointed  stick  or  fork  ; 
it  will  then  be  found  easy,  by  a  little  management,  to 
obtain  a  good  mixture  without  making  it  very  moist. 

The  luting  ought  to  be  made  as  dry  as  possible  con- 
sistent with  facility  in  working  it.  The  wetter  it  is,  the 
more  liable  to  crack  in  drying,  and  vice  versa. 

Mr.  Willis  recommends,  when  earthenware  retorts, 
&c.,  are  to  be  rendered  impervious  to  air,  the  following 
coating:  One  ounce  of  borax  is  to  be  dissolved  in  half  a 
pint  of  boiling  water,  and  as  much  slaked  lime  added  as 
will  make  a  thin  paste.  This  composition  is  to  be  spread 
over  the  vessel  with  a  brush,  and,  when  dry,  a  coating  of 
slaked  lime  and  linseed  oil  is  to  be  applied.  This  will  dry 
sufficiently  in  a  day  or  two,  and  is  then  fit  for  use. 

IRON  CEMENT. — This  mixture  is  used  for  making  per- 
manent joints  generally  between  surfaces  of  iron.  Clean 
iron  borings  or  turnings  are  to  be  slightly  pounded,  so  as 
to  be  broken  but  not  pulverised  :  the  result  is  to  be  sifted 
coarsely,  mixed  with  powdered  sal-ammoniac  and  sulphur, 
and  enough  water  to  moisten  the  whole  slightly.  The 
proportions  are — 1  sulphur,  2  sal-ammoniac,  and  80  iron. 
No  more  should  be  mixed  than  can  be  used  at  one  time. 
Mr.  Cooley  states  that  he  is  informed  by  one  of  the  first 
engineers  in  London  that  the  strongest  cement  is  made 


PLUMBAGO   AND   CLAY   CRUCIBLES.  113 

without  sulphur,  and  with  only  one  or  two  parts  of  sal- 
ammoniac  to  100  of  iron  borings  :  but  that  when  the 
work  is  required  to  dry  rapidly,  as  for  the  steam  joints  of 
machinery  wanted  in  haste,  the  quantity  of  sal-ammoniac 
is  increased  a  little,  and  a  very  small  quantity  of  sulphur 
is  added.  This  addition  makes  it  set  quicker,  but  reduces 
its  strength.  Several  excellent  cements  are  described  in 
Oooley's  '  Cyclopaedia  of  Practical  Eeceipts.'  From  these 
the  following  are  selected  : — 

BEALE'S  CEMENT. — Chalk,  60  parts  ;  lime  and  salt,  of 
each  20  parts ;  Barnsey  sand,  10  parts ;  iron  filings  or 
dust,  and  blue  or  red  clay,  of  each  5  parts.  Grind  together 
and  calcine.  This  is  patented  as  a  fire-proof  cement. 

BOILEE  CEMENT. — Dried  clay  in  powder,  6  Ibs. ;  iron 
filings,  1  lb.,  made  into  a  paste  with  boiled  linseed  oil. 
This  is  used  to  stop  leaks  and  cracks  in  iron  boilers, 
stoves,  &c. 

BRUYERE'S  CEMENT. — Clay,  3  parts  ;  slaked  lime,  1  part ; 
mix  and  expose  them  to  a  full  red  heat  for  3  hours,  then 
grind  to  powder. 

This  makes  a  good  hydraulic  cement. 

OXYCHLORIDE  OF  ZINC  CEMENT. — In  solution  of  zinc  chlo- 
ride, of  1*49  to  1*65  specific  gravity,  dissolve  3  per  cent, 
of  borax  or  sal-ammoniac,  and  then  add  zinc  oxide,  which 
has  been  heated  to  redness,  until  the  mass  is  of  a  proper 
consistency.  This  cement  becomes  as  hard  as  marble.  It 
may  be  cast  in  moulds  like  plaster  of  Paris. 

CRUCIBLES,    CUPELS,   ETC. 

The  crucibles  best  known  in  commerce  are  the  Hessian, 
the  Cornish,  the  Stourbridge,  and  the  London  clay  cru- 
cibles ;  charcoal,  plumbago,  iron,  porcelain,  platinum, 
silver,  and  gold  crucibles  are  also  required  in  small 
operations.  Of  the  clay  crucibles,  the  London  pots  are 
much  to  be  preferred,  on  account  of  their  very  refractory 
nature.  They  resist  the  action  of  fused  oxide  of  lead 
better  than  most  clay  crucibles,  and  they  are  also 
better  made  than  the  two  other  kinds,  being  much 

I 


114  PLUMBAGO   AND    CLAY   CRUCIBLES. 

smoother  and  more  regularly  formed.  They  have  the 
form  of  a  triangular  pyramid  (see  fig.  61,  crucibles  and 
cover),  and  are  made  in  such  sizes  that  they  fit  one  into 
the  other,  forming  nests.  The  triangular  form  is  very 
convenient,  because  there  are  three  spouts,  from  either  of 
which  can  be  poured  the  fused  contents  of  the  pot.  The 
Cornish  crucibles  are  circular,  and  do  not  stand  changes 
of  temperature  so  well  as  the  London  pots,  neither  can 
FIG.  6i.  they  endure  such  an  extreme 

of  heat,  for  they  agglutinate 
and  run  together  at  a  tempe- 
rature which  does  not  touch 
the  others.  Dr.  Percy  says 
they  are  more  generally  useful 
than  any  other  crucible.  The 
Hessian  pots  are  the  worst  of 
all ;  they  do  not  stand  mode- 
rate change  of  temperature 
without  risk  of  fracture,  so 
that  they  require  to  be  very 
carefully  used.  There  is  also  another  kind  of  pot  in  user 
made  of  the  same  material  as  the  London  crucibles,  termed 
a  '  skittle  pot,'  from  its  resemblance  to  the  ordinary  wooden 
skittle  or  ninepin.  They  are  exceedingly  useful  for  the 
fusion  of  large  masses  of  matter,  or  such  substances  as 
boil  or  bubble  much  when  heated.  Plumbago  or  graphite 
crucibles  are  rapidly  superseding  all  other  kinds  when 
metals  have  to  be  melted.  They  possess  many  advan- 
tages over  clay  crucibles.  Their  surface  is  very  smooth  ; 
they  are  not  liable  to  crack,  however  violent  the  changes 
of  temperature  may  be  to  which  they  are  subjected ;  they 
bear  the  highest  heat  without  softening,  and  can  be  used 
repeatedly.  Owing  to  the  reducing  property  of  the  carbon 
they  contain,  they  must  not  be  employed  when  oxidising 
actions  are  required. 

Crucibles  and  all  plumbago  fittings  for  furnaces  should 
be  of  the  '  Salamander  '  brand.  These  require  no  anneal- 
ing or  care  in  heating  up,  and  stand  strong  fluxes  better 
than  the  ordinary  make. 


PLUMBAGO   AND    CLAY   CRUCIBLES,  115 

The  Patent  Plumbago  Crucible  Company  have  recently 
introduced  a  very  excellent  fluxing  crucible.  It  is  made 
of  fine  white  china  clay,  is  perfectly  smooth  inside  and 
out,  and  will  stand  very  high  temperatures  without  soften- 
ing. 

Stourbridge  clay  crucibles  are  not  much  used.  They 
require  the  greatest  care  in  using  them,  and  are  spoilt 
after  the  first  operation. 

Porcelain  crucibles  are  not  used  in  large  assaying  or 
metallurgical  operations,  but  they  are  invaluable  in  small 
laboratory  experiments.  They  are  practically  infusible, 
are  little  liable  to  crack,  and  are  almost  unacted  on  by 
reagents  and  fluxes.  In  many  cases  they  will  replace  the 
more  expensive  platinum  crucibles,  and  where  easily  re- 
ducible metals  are  under  treatment  they  must  be  used  in 
preference  to  platinum. 

Crucibles,  in  order  to  be  perfect  and  capable  of  being 
used  indifferently  for  any  operation,  ought  to  possess  the 
four  following  qualities  :  first,  not  to  break  or  split  when 
exposed  to  sudden  changes  of  temperature  ;  secondly,  to 
be  infusible  ;  thirdly,  to  be  only  slightly  attacked  by  the 
fused  substances  they  may  contain  ;  fourthly  and  lastly,  to 
be  impermeable,  or  nearly  so,  to  liquids  and  gases.  But 
as  it  is  very  difficult  to  unite  all  these  qualifications, 
various  kinds  of  pots  are  made  to  fulfil  one  or  more  of 
them. 

In  order  to  render  crucibles  capable  of  withstanding 
changes  of  temperature  without  breaking,  a  certain  pro- 
portion of  substances  infusible  by  themselves  is  mixed 
with  the  pasty  clay ;  sand,  flint,  fragments  of  old  crucibles, 
black-lead,  and  coke  are  used  for  this  purpose.  They  are 
reduced  to  a  state  of  division  more  or  less  fine,  according 
to  the  grain  of  the  clay  paste.  For  ordinary  pots  the 
powder  ought  not  to  be  very  fine  ;  but  for  porcelain  cru- 
cibles it  ought  to  be  as  fine  as  flour.  The  choice  of  these 
various  bodies  depends  upon  the  use  for  which  the  crucible 
is  intended. 

The  most  refractory  crucibles  are  those  made  with  the 
pure  clays,  or  such  as  contain  little  or  no  , oxide  of  ironr 

i  2 


116  PLUMBAGO  AND    CLAY   CRUCIBLES. 

and  especially  those  free  from  calcareous  matters.  Amongst 
clays,  the  best  are  those  which  contain  most  silica  ;  never- 
theless, these  are  not  absolutely  infusible,  and  in  the  high 
temperature  of  a  wind  furnace  they  sometimes  soften  so 
much  as  actually  to  fall  into  a  shapeless  mass.  This  defect, 
as  before  stated,  can  be  in  some  measure  diminished  by 
mixing  with  the  clay  a  quantity  of  graphite  or  coke  ; 
either  of  these  substances  forms  a  kind  of  solid  skeleton, 
which  retains  the  softened  clay,  and  prevents  its  falling- 
out  of  shape. 

Coke  and  black-lead  are  more  efficacious  than  sand, 
because  they  have  no  action  on  clay,  whilst  sand  forms  a 
fusible  compound  with  it.  If  too  large  a  quantity  of 
black-lead  or  coke  be  employed,  it  gradually  consumes  in 
the  fire,  and  the  pots  become  porous,  and  break  at  the 
least  movement.  Wood  charcoal  can  be  used  instead  of 
black-lead  or  coke,  but  is  not  so  good,  as  it  burns  more 
readily. 

Black-lead  crucibles  are  generally  composed  of  1  part 
of  refractory  clay,  and  from  2  to  3  of  black-lead.  These 
pots  withstand  all  possible  changes  of  temperature  without 
cracking,  and  their  form  is  rarely  changed  by  the  heat ; 
not  because  they  are  absolutely  infusible,  but  because  they 
are  supported  by  the  skeleton  of  graphite. 

Crucibles  into  whose  composition  carbonaceous  matters 
enter,  reduce  any  oxides  that  may  be  heated  in  them,  and 
hence  are  inconvenient  in  certain  cases.  They  can,  neverthe- 
less, be  employed  in  all  cases  by  giving  them  a  lining  of  clay, 
which  must  be  tolerably  thick,  and  well  dried  before  use. 

Earthen  crucibles  which  have  not  been  baked  at  a 
white  heat  are  more  or  less  permeable  to  liquids  and 
gases,  according  to  the  grain.  In  order  to  render  them 
impermeable  to  liquids,  they  must  be  heated  to  such  a 
temperature  as  will  suffice  to  fuse  the  outside.  When 
treated  in  this  way,  however,  they  are  very  liable  to  crack 
with  sudden  changes  of  temperature :  the  best  method, 
therefore,  of  rendering  them  capable  of  containing  water, 
•&c.,  is  to  coat  them  with  the  mixture  of  borax  and  lime 
described  as  Willis's  lute. 


GOOD   AXD    BAD    CRUCIBLES.  117 

In  order  that  crucibles  may  resist  the  corrosive  action 
of  the  fused  substances  contained  within  them,  they  must 
be  as  compact  as  possible,  and  the  substance  of  which 
they  are  made  must  have  little  or  no  tendency  to  combine 
with  the  fused  contents.  The  metals  and  their  non-oxi- 
dised compounds  attack  neither  clay  nor  black-lead  ;  but 
there  are,  nevertheless,  some  metallic  substances — galena, 
for  instance — which,  without  exercising  any  chemical 
action,  on  earthy  matters,  have  the  property  of  filtering 
through  their  pores. 

The  readily  reducible  oxides  gradually  corrode  black- 
lead  crucibles  and  those  pots  into  the  composition  of  which 
coke  enters,  by  burning  the  carbonaceous  matter.  The 
greater  number  of  these  oxides,  the  alkalies,  earths,  and 
glasses  (which  are  fusible  silicates,  borates,  &c.),  act  more 
or  less  powerfully  on  the  earthy  base  of  all  crucibles  ;  so 
that  these  substances  are  most  difficult  to  keep  in  fusion 
for  any  length  of  time.  They  attack  the  crucible  layer 
by  layer,  dissolving  the  substance  of  which  it  is  composed, 
and  after  a  lapse  of  time  rendering  it  so  thin  that  it  can- 
not withstand  the  pressure  of  the  molten  mass  within  it ; 
and  the  fracture  of  the  pot,  and  consequent  loss  of  con- 
tents, is  inevitable. 

Under  the  same  circumstances,  all  those  crucibles 
whose  texture  is  loose  are  more  readily  corroded  than 
those  with  a  firm,  compact  body  ;  because  the  corrosive 
substance  filters  to  a  certain  depth  in  the  former  crucibles, 
and  in  consequence  has  a  larger  surface  to  act  upon  than 
when  it  is  contained  in  a  compact  pot. 

Earthen  crucibles  may  be  assayed  by  noticing  the  time 
they  will  contain  fused  litharge,  which  exercises  a  very 
corrosive  action  on  them,  honeycombing  them  in  all  di- 
rections ;  and  those  pots  which  contain  it  longest  without 
undergoing  much  damage,  may  be  considered  the  best. 
However,  this  method  of  assay  is  not  exact,  even  by  taking 
into  account  the  thickness  of  the  pot,  for  litharge  runs 
through  crucibles :  first,  because  it  is  very  fusible,  and 
easily  filters  through  their  pores  ;  and  secondly,  it  has  the 
property  of  forming  fusible  compounds  with  all  the  sili- 


118  GOOD    AND   BAD    CRUCIBLES. 

cates  by  combining  with  them.  From  these  remarks  it 
will  be  evident  that  a  crucible  whose  grain  is  loose  will 
readily  allow  litharge  to  pass  through  it,  however  slightly 
its  substance  may  be  fusible  or  acted  on ;  or,  on  the  con- 
trary, it  may  be  very  easily  acted  on  (even  when  infusible) 
when  it  has  an  extremely  fine  grain ;  so  that  the  prompti- 
tude with  which  a  crucible  is  pierced  by  litharge  bears 
no  relation  to  its  fusibility.  A  crucible  of  pure  quartz 
will  be  very  readily  attacked  by  litharge,  because  the 
latter  has  much  affinity  for  silica,  and  the  simple  silicates 
of  lead  ^are  all  very  fusible  ;  whilst  a  crucible  composed  'of 
silica,  alumina,  and  lime,  which  by  itself  is  very  fusible, 
would  be  corroded  less  rapidly,  because  the  oxide  of  lead  has 
much  less  affinity  for  the  earths  than  it  has  for  the  silica  ; 
moreover,  it  forms  less  fusible  compounds  with  the  earths 
than  with  silica  alone.  The  assay  of  crucibles  with  li- 
tharge, if  not  of  use  in  ascertaining  their  degree  of  fusi- 
bility, fulfils  perfectly  its  object  when  it  is  wished  to  prove 
the  resistance  a  crucible  has  to  the  corrosive  action  of 
various  bodies  in  a  state  of  fusion ;  for  of  all  fusible  sub- 
stances, none  exercise  such  a  powerful  action  on  earthy 
matters  as  litharge. 

Crucibles  ought  not  only  to  resist  the  corrosive  action 
of  those  bodies  they  may  contain,  but  also  that  of  the  ash 
produced  by  the  combustion  of  the  fuel  in  which  they 
may  be  placed.  These  ashes  being  often  calcareous,  alka- 
line, or  ferruginous,  act  on  the  clayey  part  of  the  crucibles 
exactly  as  the  fluxes.  Whence  it  follows,  that  those  cru- 
cibles which  contain  litharge  longest  will  also  resist  the 
action  of  the  fluxes  best. 

In  order  to  ascertain  the  fusibility  of  a  crucible,  a 
direct  experiment  must  be  made,  either  by  heating  a  piece 
in  a  crucible  lined  with  charcoal,  and  ascertaining  if  its 
angles  be  rounded,  if  its  substance  has  become  translucent, 
&c.  ;  or,  better  still,  by  heating  the  crucible  to  be  assayed 
with  another  whose  properties  are  well  known. 

As  to  permeability,  it  may  approximately  be  ascer- 
tained by  filling  two  crucibles  with  water,  and  noting  what 
length  of  time  is  required  to  empty  them  completely ;  the 


CHARCOAL   CEUCIBLES.  119 

crucible  which  contains  it  longest  being,  of  course,  the 
least  permeable. 

To  prove  if  a  crucible  be  able  to  sustain  great  changes 
of  temperature  without  breaking,  introduce  it,  perfectly 
cold,  into  a  furnace  full  of  lighted  coal :  take  it  out  when 
reddish  white,  and  expose  it  to  a  current  of  cold  air  pro- 
duced by  a  bellows  or  otherwise  :  if  it  stand  these  trials, 
it  may  be  heated  afresh  and  plunged  red-hot  into  water, 
and,  if  it  be  not  broken,  placed  immediately  in  the  fire. 
The  best  pots  support  all  these  operations  without  break- 
ing ;  but  it  often  happens  that  they  are  filled  with  innu- 
merable small  fissures,  through  which  fused  matters  can 
pass.  This  can  be  ascertained  by  fusing  rapidly  in  the 


assay  pot  a  quantity  of  litharge  :  if  these  fissures  be  pre- 
sent, the  fused  oxide  will  readily  filter  through  them. 

CHARCOAL  CRUCIBLES. — As  all  oxidised  matters  act  readily 
on  clay  pots,  and  a  great  number  of  the  metals  and  their 
compounds  adhere  to  them,  they  have  long  since  been 
replaced,  under  certain  circumstances,  by  charcoal  cru- 
cibles, which  do  not  possess  these  disadvantages.  The 
older  assay ers  used  merely  a  piece  of  charcoal,  with  a 
hole  made  in  it,  and  then  bound  round  with  iron  or  other 
wire.  The  use  of  these  has,  however,  been  abandoned  for 
some  time,  and  earthenware  crucibles  lined  with  charcoal 
have  been  substituted  (see  fig.  62,  a,  b,  and  c).  These  may 
be  considered  as  charcoal  pots  enveloped  with  refractory 


120  LINED    CRUCIBLES. 

clay  ;  they  are  solid,  always  free  from  cracks,  and  easy  of 
preparation,  and  they  have  the  same  properties  as  the 
solid  charcoal  crucibles  without  their  inconveniences. 

In  order  to  prepare  these  crucibles,  the  charcoal  must  be 
chosen  carefully,  so  as  to  contain  no  foreign  substances;  it 
must  be  pulverised  and  passed  through  a  sieve  ;  the  powder 
moistened  with  water  or  treacle,  mixed  with  a  spatula,  and 
then  kneaded  with  the  fingers  until  it  just  adheres,  and 
forms  adhesive  lumps  without  being  sufficiently  wet  to 
adhere  to  the  hand.  Some  advise  the  addition  of  gum  to 
the  water  with  which  the  charcoal  is  moistened.  The 
crucible  is  moistened  slightly  by  being  plunged  into  water, 
and  withdrawn  as  speedily  as  possible,  and  about  half  an 
inch  in  depth  of  the  charcoal  paste,  prepared  as  above,  is 
placed  in  it ;  the  paste  is  then  pressed  firmly  down,  by 
means  of  a  wooden  pestle :  the  blows  are  to  be  slight  at 
first,  and  then  increase  in  force  until  it  is  as  firm  as  possible  : 
another  layer  is  then  applied  and  pressed  as  before,  and 
the  process  repeated  until  the  crucible  is  quite  full,  taking 
great  care  to  render  all  as  firm  as  possible,  especially  at 
the  sides.  In  order  to  make  each  layer  adhere  firmly  to 
the  other,  the  surface  must  be  scratched  rather  deeply 
with  the  point  of  a  knife  before  a  new  layer  is  applied. 
When  the  crucible  is  completely  filled,  a  hole  is  to  be 
scooped  in  the  charcoal  of  about  the  form  of  the  pot.  The 
sides  are  then  rendered  smooth  by  friction  with  a  glass 
rod.  This  is  absolutely  necessary,  so  that  the  metallic 
globules  produced  in  an  assay  may  not  be  retained  by  the 
asperities  of  the  lining,  but  may  be  readily  enabled  to  unite 
into  one  button.  When  a  lined  charcoal  pot  is  well  made, 
its  sides  are  very  smooth  and  shining.  For  ordinary  use, 
the  lining  may  be  f  ths  of  an  inch  thick  at  the  bottom  and 
-|th  or  so  at  the  sides  :  but  in  some  cases,  for  instance, 
when  the  substance  to  be  fused  is  capable  of  filtering 
through  the  lining  and  attacking  the  pot  as  a  flux,  it  must 
be  at  least  twice  the  above  thickness  in  every  part. 

Lined  crucibles  have  many  advantages  over  plain 
crucibles.  The  lining  gives  them  greater  solidity,  and 
prevents  a  loss  of  shape  when  softened  ;  for  plain  crucibles 


LIME    CRUCIBLES.  12i 

are  always  three-fourths  empty  when  their  contents  are 
fused,  on  account  of  contraction  in  volume  :  the  pots  then 
have  nothing  to  sustain  their  sides  when  they  soften  to- 
wards the  end  of  the  assay,  at  which  period  the  highest 
temperature  is  employed.  Besides,  vitreous  matters  do 
not  penetrate  the  lining,  and  exercising  no  action  on  it,, 
can  be  obtained  in  a  state  of  purity,  and  the  exact  weight 
determined :  if  fused  in  a  plain  pot,  the  weight  could  not 
be  ascertained,  because  a  portion  would  adhere  to  the 
sides,  and  the  resulting  mass  would  not  be  pure,  having 
taken  up  a  portion  of  the  crucible  in  which  the  fusion  was 
effected. 

The  lining,  too,  effects  the  reduction  of  certain  metallic 
oxides  by  cementation,  and  does  away  with  the  necessity 
of  adding  powdered  charcoal  to  the  body  to  be  reduced. 
This  property  is  very  valuable,  because,  when  an  oxide  is 
reduced  by  mixing  it  with  charcoal,  an  excess  must  always 
be  employed,  and  this  excess  remains  with  the  metal,  and 
prevents  its  exact  weight  from  being  ascertained.  No 
oxidising  substances  or  bodies  which  readily  part  with 
oxygen  (oxide  of  copper,  for  example)  must  be  calcined  in 
a  plumbago  or  charcoal-lined  crucible,  unless  indeed  the 
chemical  union  of  the  charcoal  with  the  oxygen  is  desired. 

LIME  CRUCIBLES. — Some  years  ago  Deville  proposed  the 
use  of  crucibles  cut  out  of  solid  blocks  of  pure  lime,  in 
order  to  prevent  the  introduction  of  carbon  and  silicon 
into  metals  and  alloys  during  the  process  of  fusion. 

The  results  of  experiments  made  with  such  crucibles 
were  found  to  be  extremely  satisfactory,  and  metals  fused 
therein,  as  iron,  manganese,  nickel,  cobalt,  &c.,.  were 
obtained  far  purer  and  more  malleable  and  ductile  than 
when  fused  in  the  usual  clay  or  brasqued  crucibles.  Un- 
less, however,  the  crucibles  required  were  of  very  small 
size,  it  was  found  difficult  to  obtain  blocks  of  lime  for 
shaping  them  sufficiently  large  and  free  from  flaws  ;  and 
experiment  showed  a  considerable  loss,  both  by  breakage 
when  shaping  them,  and  by  their  cracking  when  in  the 
furnace.  In  order  to  obviate  this,  trials  were  made  with 
clay  crucibles  lined  with  lime,  but  ineffectually,  as  these 


122  LIME    CEUCIBLES. 

crucibles  invariably  melted  down  before  the  requisite  heat 
was  arrived  at — a  result  due  to  the  action  of  the  lime 
itself  upon  the  outer  clay  crucible. 

Mr.  David  Forbes,  F.E.S.,  has  published  in  the  '  Chemi- 
cal News  '  the  result  of  some  very  valuable  experiments 
on  this  subject.  The  arrangement  he  proposes  fully 
answers  the  purpose,  the  crucibles  being  capable  of  stand- 
ing the  heat  of  melted  wrought  iron  or  cobalt  without 
fusion  or  cracking,  as  well  as  of  being  made  of  any  reason- 
able size. 

A  clay  crucible  of  somewhat  larger  capacity  than  the 
desired  hme  one,  is  filled  with  common  lamp-black,  com- 
pressing the  same  by  stamping  it  well  down.  The  centre 
is  then  cut  out  with  a  knife  until  a  shell  or  lining  of  lamp- 
black is  left  firmly  adherent  to  the  sides  of  the  crucible, 
and  about  half  an  inch  or  less  in  thickness,  according  to 
the  size  of  the  crucibles  ;  this  lining  is  now  well  rubbed 
down  with  a  thick  glass  rod  until  its  surface  takes  a  fine 
glaze  or  polish,  and  the  whole  cavity  is  then  filled  up  with 
finely  powdered  caustic  lime,  thoroughly  pressed  down, 
and  a  central  cavity  cut  out  as  before  ;  or  the  lime  powder 
may  be  at  once  rammed  down  round  a  central  core  of  the 
dimensions  of  the  intended  lime  crucible. 

This  lime  lining  is  naturally  rather  soft  before  being 
placed  in  the  furnace,  but  upon  heating,  it  agglutinates,  and 
forms  a  strong  and  compact  crucible,  which  is  prevented 
from  acting  upon  the  outer  one  by  the  interposed  thin  layer 
of  lampblack,  and  at  the  end  of  the  experiment  it  generally 
turns  out  as  solid  and  compact  as  those  made  in  the  lathe. 

Experiments  made  with  such  crucibles,  even  up  to 
dimensions  containing  several  pounds  of  metal,  have  proved 
them  extremely  well  suited  for  these  operations,  and  doubt- 
less similar  crucibles  could  be  made,  lined  with  magnesia 
or  alumina  as  required.  In  some  cases  ordinary  black- 
lead  crucibles,  lined  with  powdered  lime,  magnesia,  or 
alumina,  might  possibly  be  found  to  answer. 

Having  frequently  used  lime  crucibles  in  metallurgical 
operations,  and  having  met  with  the  inconvenience  pointed 
out  by  Mr.  Forbes,  the  editor  can  appreciate  the  great 


ALUMINA   CEUCIBLES.  123 

value  of  his  improvement.  It  is  one  which  cannot  fail  to 
be  extensively  adopted  in  metallurgical  laboratories. 

In  certain  particular  experiments,  crucibles  are  lined 
with  other  bodies  besides  charcoal  and  lime,  such  as  silica, 
alumina,  magnesia,  or  chalk,  by  merely  moistening  their 
respective  powders  with  water,  and  applying  the  paste  as 
above  described  for  the  charcoal.  A  slight  layer  of  chalk 
lessens  the  liability  of  attack  from  fused  litharge. 

ALUMINA  CRUCIBLES  are  strongly  to  be  recommended  in 
many  metallurgical  operations.  They  are  made  in  the 
following  manner.  Ammonia  alum  is  ignited  at  a  full  red 
or  white  heat,  when  it  leaves  behind  pure  alumina  in  a 
dense  compact  form :  this  is  to  be  finely  powdered.  To  a 
solution  of  another  portion  of  ammonia  alum  in  water, 
ammonia  is  added,  when  alumina  is  precipitated  in  a  gela- 
tinous state  :  this  is  to  be  washed  until  free  from  sulphate 
of  ammonia.  The  dense  alumina  is  then  mixed  with  water 
and  worked  up  into  a  paste,  the  precipitated  gelatinous 
alumina  being  kneaded  in  from  time  to  time ;  this  gives 
coherency :  and  when  sufficient  has  been  added  (which 
must  be  ascertained  experimentally),  the  mass  may  be 
moulded  into  shape.  These  crucibles  require  slow  and 
careful  drying ;  but  they  well  repay  all  the  care  which  is 
bestowed  on  them,  for  they  do  not  readily  crack,  are 
attacked  by  very  few  fluxes,  give  out  no  impurities  to 
metals  which  are  melted  in  them,  and  are  infusible  at  the 
highest  heat  of  the  furnace. 

MAGNESIA  CRUCIBLES  AND  BRICKS.  —  M.  H.  Caron  has 
pointed  out  the  advantages  which  would  accrue  to  metal- 
lurgy from  the  employment  of  magnesia  as  a  refractory 
material.  Formerly  the  high  price  of  this  earth  appeared 
likely  to  confine  it  to  the  laboratory.  Now,  circumstances 
have  happily  changed ;  recent  modifications  introduced 
into  the  manufacture  of  cast  steel,  and  especially  the  em- 
ployment of  Siemens's  furnace  and  Martin's  process,  abso- 
lutely demand  more  refractory  bricks  than  those  at  present 
in  use,  irrespective  of  price.  On  the  other  hand,  native 
carbonate  of  magnesia,  which  formerly  cost  ~LQL  the  ton, 
may  now  be  obtained  at  the  price  of  21.  15s.  delivered  at 


124  MAGNESIA   CRUCIBLES   AND   BRICKS. 

Marseilles,  or  delivered  at  Dunkirk.  Calcination  at  the 
place  where  the  carbonate  is  obtained  may  still  further 
reduce  its  price.*  The  following  is  M.  Caron's  process- 
for  its  agglomeration,  which  may  be  employed  by  the 
chemist  for  the  ready  preparation  of  refractory  vessels 
of  all  forms  ;  by  the  physicist  to  obtain  pencils  for  oxy- 
hydrogen  lighting  purposes ;  and  also  by  the  manu- 
facturer, to  replace,  in  some  cases,  fire-bricks  which  have 
become  insufficient  in  carrying  out  different  processes- 
of  heating. 

The  magnesia  which  he  employs  comes  from  the  island 
of  Elba,  where  it  is  found  in  considerable  quantities  as  a 
native  carbonate,  white,  very  compact,  and  of  great  hard- 
ness. This  carbonate  contains  traces  of  lime,  silica,  and 
iron ;  it  is,  besides,  interspersed  sometimes  with  serpentine 
and  large  plates  of  silica,  which  would  diminish  the  in- 
fusibility  of  the  substance,  and  render  it  especially  unfit 
for  oxyhydrogen  illumination  if  their  removal  is  neglected. 
These  plates  are,  however,  easily  recognised,  and  may 
be  readily  separated,  even  in  working  on  the  large  scale, 
In  the  case  of  refractory  bricks,  the  presence  of  a  small 
quantity  of  these  foreign  bodies  would,  at  the  most,  give 
rise,  under  the  influence  of  the  highest  temperatures,  to  a 
slight  vitrification,  offering  no  serious  inconvenience. 

Before  powdering  the  carbonate,  it  is  advisable  to  bake 
it  at  the  temperature  necessary  for  the  expulsion  of  the 
carbonic  acid  ;  the  material  then  becomes  very  friable, 
and  may  be  pulverised  more  easily.  It  is  then  possible  to 
separate  the  serpentine  and  silica,  which  do  not  become 
friable  under  the  influence  of  heat.  This  preliminary 
treatment  does  not  permit  of  the  agglomeration  of  the 
magnesia,  and,  even  were  this  difficulty  to  be  overcome,  a 
temperature  higher  than  that  of  the  original  calcination 
would  cause  an  enormous  contraction,  producing  fissures 
and  alterations  in  shape  which  would  interfere  with  the 
use  of  this  substance.  It  is  therefore  indispensable,  before 
moulding  the  magnesia,  to  submit  it  to  a  very  intense  heat, 

*  This  preliminary  calcination  requires  less  heat  than  burning  lime,  and 
diminishes  the  weight  of  the  carbonate  one-half. 


MAGNESIA   CKUCIBLES   AND    BKICKS.  125 

at  least  equal  to  that  which  it  is  intended  to  support  sub- 
sequently. 

Thus  calcined  it  is  not  plastic,  its  appearance  is  sandy, 
and  compression  does  not  cause  it  to  acquire  any  cohesion ; 
a  mixture  of  magnesia,  less  calcined,  imparts  to  it  this 
quality.  The  quantity  of  the  latter  to  be  added  necessarily 
varies  with  the  degree  of  calcination  of  the  two  magnesias ; 
it  is  scarcely  one-sixth  of  the  weight  of  that  which  has 
been  exposed  to  the  temperature  of  melting  steel.  It  only 
now  remains  to  moisten  it  with  10  or  15  per  cent,  of  its 
weight  of  common  water,  and  strongly  compress  it  in  iron 
moulds,  as  adopted  in  making  artificial  fuel.  The  brick 
produced  in  this  operation  hardens  on  drying  in  the  air, 
and  becomes  still  more  resisting  when  it  is  subsequently 
calcined  at  a  red  heat.  The  same  process  would  appeal- 
practicable,  varying  the  form  of  the  moulds,  for  obtaining 
crucibles  of  great  capacity  ;  but  compression  is  difficult  in 
large  masses,  as  well  as  when  the  moulds  have  a  large 
surface,  as  the  magnesia  adheres  strongly  to  the  sides. 
Although  M.  Caron  has  been  able  to  obtain  small  crucibles 
for  the  laboratory,  he  does  not  consider  this  process 
adapted  to  make  the  large  crucibles  employed  in  steel 
melting.  In  this  and  other  cases  it  is  preferable  to  ag- 
glomerate the  magnesia  in  the  humid  way. 

To  endow  magnesia  with  a  sort  of  plasticity,  advantage 
is  taken  of  a  property  of  this  earth  pointed  out  in  '  Ber- 
zelius's  Chemistry.'  When  strongly  calcined  and  then 
moistened,  it  hardens  in  drying.  This  fact  is  doubtless 
due  to  a  hydration  which  takes  place  without  sensible  in- 
crease of  temperature.  When  solidified  in  this  manner 
the  magnesia  only  loses  the  assimilated  water  at  a  high 
temperature.  Then  calcination  not  only  does  not  disin- 
tegrate it,  but,  on  the  contrary,  confers  upon  it  a  hardness 
and  resistance  comparable  to  those  of  ordinary  crucibles 
after  their  baking.  This  being  understood,  the  appli- 
cation of  this  fact  is  obvious.  Thus,  the  magnesia  to  be 
employed  in  the  manufacture  of  crucibles  should  only  be 
moistened,  moulded  into  shape,  dried,  and  then  ignited. 
Por  the  construction  of  steel  melting  furnaces,  a  paste  of 


126  PLATINUM    CRUCIBLES. 

moistened  magnesia  should  be  plastered  over  the  walls  ;  it- 
will  become  ignited  in  due  course  without  any  particular 
precautions  being  taken.  It  sometimes  happens,  however, 
either  owing  to  the  magnesia  being  too  much  or  too  little 
hydrated,  or  owing  to  its  containing  siliceous  matter,  that 
the  vessels  before  or  after  firing  do  not  possess  quite  the 
desirable  solidity ;  they  should  then,  to  acquire  this,  be 
simply  moistened  in  a  cold  saturated  solution  of  boracic 
acid,  dried,  and  then  fired  as  before.  This  operation  does 
not  render  the  magnesia  more  fusible ;  it  only  causes  the 
grains  of  the  substance  to  cohere  more  strongly  together. 

Magnesia,  very  pure,  strongly  calcined  and  finely  pul- 
verised, may  be  employed  in  the  form  of  paste  (barbotine) 
and  yield  the  most  delicate  and  translucent  crucibles,  as- 
well  as  the  sharpest  and  most  complicated  impressions. 

MALLEABLE  IRON  CRUCIBLES  are  often  very  serviceable  in 
assays  of  fusibility,  and  of  certain  selinides  and  sulphides, 
as  in  assays  of  galena  or  ordinary  lead  ore.  They  are 
either  made  of  hammered  sheet  iron,  or  by  plugging  up 
small  iron  tubes,  as  gun-barrels,  &c.  The  latter  are  pre- 
ferable, because  thick  solid  crucibles  can  be  used  a  number 
of  times,  whilst  the  others  are  necessarily  very  thin  and 
can  be  used  only  once.  Whenever  iron  crucibles  are  em- 
ployed at  a  very  high  temperature,  they  must  be  placed 
in  those  of  earthenware,  which  protect  them  from  the 
oxidising  action  of  the  air  ;  but  when  they  are  not  heated 
above  the  temperature  of  a  copper  assay,  they  may  be  used 
naked,  if  tolerably  thick. 

For  assays  at  the  above  temperature,  cast-iron  crucibles 
may  be  employed  with  advantage,  instead  of  wrought-iron, 
because  they  are  very  nearly  as  good,  and  much  less 
expensive. 

PLATINUM  CRUCIBLES. — Platinum  crucibles  are  invalu- 
able in  a  laboratory.  Few  pieces  of  apparatus  are  used 
so  frequently  by  the  chemist.  Their  chief  use  is  in  the 
ignition  of  precipitates  and  the  decomposition  of  siliceous 
minerals  by  fusion  with  alkaline  carbonates.  They  are 
preferable  to  porcelain,  as  not  being  fragile  and  being 
more  readily  heated  to  redness  over  the  gas  or  spirit  flame. 


PLATINUM   CRUCIBLES.  127 

Their  most  convenient  size  is  1^  inch  high  and  1J  inch 
wide  at  the  top. 

In  employing  a  crucible  for  the  incineration  of  filters 
in  quantitative  assays  by  the  wet  way,  it  sometimes  happens 
(as,  for  instance,  with  chloride  of  silver  or  sulphate  of  lead) 
that  the  employment  of  platinum  is  inadmissible.  In  these 
cases  thin  porcelain  crucibles  must  be  used.  The  analyst 
will,  however,  frequently  experience  difficulty,  owing  to 
the  extreme  slowness  with  which,  in  many  cases,  the  last 
portions  of  the  carbon  of  a  filter  are  consumed  when 
ignited  in  a  porcelain  crucible.  It  does  not  appear,  how- 
ever, that  the  following  simple  method  of  obviating  the 
difficulty,  as  practised  in  the  laboratory  of  Professor 
Sheerer,  in  Freiburg,  has  ever  received  the  publicity  which 
it  deserves.  Whenever  a  filter  upon  which  a  substance 
capable  of  injuring  platinum  has  been  collected,  has  to  be 
incinerated,  the  porcelain  crucible  or  capsule  in  which  the 
process  is  to  be  conducted  should  be  placed  within  a  vessel 
of  platinum  of  similar  form,  and  the  whole  ignited  in  the 
usual  way.  Whether  the  greatly  accelerated  rapidity  of 
combustion  of  the  carbon  which  ensues  depends  upon  a 
more  equal  distribution  of  heat  brought  about  by  the 
greater  conductirig  power  of  the  metal — an  explanation 
which  is  current  for  the  somewhat  analogous  case  of  copper- 
coated  glass  flasks — or  whether,  as  seems  probable,  the 
power  of  the  porcelain  vessel  to  absorb  heat  be  really 
increased  by  the  interposition  of  the  platinum  ;  whether 
both  these  causes  be  of  influence,  or,  the  result  depends 
upon  another  less  apparent  reason  ;  or  finally,  whether 
vessels  of  some  other  metal  would  not  be  preferable  to 
those  of  platinum,  are  questions  which  are  open  to  dis- 
cussion. 

Fresenius  gives  the  following  excellent  directions  as  to 
the  preservation  of  platinum  crucibles.  The  analyst  should 
acquire  the  habit  of  cleaning  and  polishing  the  platinum 
crucible  always  after  using  it.  This  should  be  done,  as 
recommended  by  Berzelius,  by  friction  with  moist  sea-sand, 
whose  grains  are  all  round,  and  do  not  scratch.  The 
writer  has  found  this  method  to  answer  extremely  well. 


128  PLATINUM   CRUCIBLES. 

The  sand  is  rubbed  on  with  the  finger,  and  the  desired 
effect  is  produced  in  a  few  minutes.  The  adoption  of  this 
habit  is  attended  with  the  pleasure  of  always  working  with 
a  bright  crucible,  and  the  profit  of  prolonging  its  existence. 
This  mode  of  cleaning  is  all  the  more  necessary  when  one 
ignites  over  gas-lamps,  since  at  this  high  temperature 
crucibles  soon  acquire  a  grey  coating,  which  arises  from 
a  superficial  loosening  of  the  platinum.  A  little  scouring 
with  sea-sand  readily  removes  the  appearance  in  question, 
without  causing  any  notable  diminution  in  the  weight  of 
the  crucible. 

The  ordinary  Bunsen  burner  is  known  to  act  upon  the 
surface  of  platinum  vessels  brought  into  contact  with  the 
inner  line  of  the  flame  ;  the  metal  loses  its  polish,  becom- 
ing superficially  porous  and  spongy,  and  requires  the  use 
of  the  burnisher  to  bring  it  back  to  its  original  state.  This 
alteration  of  the  surface  Mr.  Dexter  has  found  to  be  at- 
tended with  a  change  of  weight,  so  that  for  some  years  he 
has  used  a  lamp  of  different  construction  for  the  heating 
of  platinum  crucibles  in  analytical  operations.  Such  a 
lamp  may  be  made  by  removing  the  air-tube  of  a  common 
Bunsen  lamp,  and  putting  in  its  place  a  somewhat  longer 
one  of  glass  or  iron  of  about  12  millimetres  internal  dia- 
meter. The  gas  jet  should  have  a  single  circular  aperture, 
and  be  in  proper  proportion  to  the  diameter  of  the  tube, 
which  may  be  held  in  any  of  the  ordinary  clamp  supports. 
The  tube  being  raised  sufficiently  above  the  jet  to  allow 
free  entrance  of  air,  and  a  full  stream  of  gas  let  on,  a  '  roar- 
ing '  flame  is  produced,  of  which  the  interior  blue  cone  is 
pointed,  sharply  defined,  and  extends  only  about  half  an 
inch  from  the  top  of  the  tube.  A  polished  platinum  sur- 
face is  not  acted  upon  by  this  flame,  provided  it  be  not 
brought  into  contact  with  the  interior  cone.  In  the 
Bunsen  burner,  as  usually  made,  the  supply  of  air  depends 
upon  the  diameter  of  the  tube,  the  holes  at  its  base  being 
more  than  sufficient  to  supply  the  draught.  With  the 
wider  tube  it  is  necessary  to  limit  the  admission  of  air  by 
depressing  the  tube  upon  the  lamp  when  the  force  of 
the  gas  is  diminished.  Otherwise  the  proportion  becomes 


PLATINUM   CRUCIBLES.  129 

such  that  an  explosive  mixture  is  formed ;  for  this  reason 
it  is  more  convenient  to  use  an  arrangement  in  which  the 
access  of  air  can  be  regulated  by  an  exterior  tube  sliding 
obliquely  downward  over  the  air-apertures.  The  gas  jet 
should  be  on  a  level  with  the  top  of  these  apertures,  which 
must  be  much  larger  than  those  of  the  ordinary  Buiisen's 
burner.  On  account  of  the  liability  to  explode  and  burn 
at  the  jet  inside,  the  lamp  is  not  well  adapted  for  ordinary 
use  ;  but  for  ignition  of  crucibles,  working  of  glass,  &c., 
it  has  proved  efficient  and  practical. 

In  connection  with  some  sensible  remarks  upon  the 
before-mentioned  use  of  sand  in  cleaning  platinum  cru- 
cibles, Erdmann  explains  in  the  following  way  the  cause 
of  this  grey  coating  which  forms  upon  platinum  crucibles 
whenever  they  are  ignited  in  the  flame  of  Bunsen's  gas- 
burner.  This  coating  has  given  rise  to  much  annoyance 
and  solicitude  among  chemists.  Indeed  it  has  often  been 
asserted  that  the  use  of  Bunsen's  burner  is  unadvisable  in 
quantitative  analysis,  since  by  means  of  it  the  weight  of 
platinum  crucibles  is  altered  and  the  crucibles  themselves 
injured.  The  coating  is  produced  most  rapidly  when  the 
crucible  is  placed  in  the  inner  cone  of  the  flame,  and  the 
more  readily  in  proportion  as  the  pressure  under  which 
the  gas  is  burned  is  higher.  Having  found  it  advantageous 
to  maintain,  by  means  of  a  special  small  gas-holder,  a 
pressure  of  four  or  five  inches  upon  the  gas  used  in  his  own 
laboratory,  Erdmann  observed  that  the  strong  gas-flame 
thus  afforded  immediately  occasioned  the  formation  of  a 
dull  ring  upon  the  polished  metal  placed  in  the  inner 
flame,  this  ring  being  especially  conspicuous  when  the 
crucible  becomes  red-hot ;  it  increased  continually,  so 
that  after  long-continued  ignition  the  whole  of  the  bottom 
of  the  crucible  was  found  to  be  grey  and  with  its  lustre 
dimmed. 

The  ring  is  caused  neither  by  sulphur,  as  some  have 
believed,  nor  by  a  coating  of  inorganic  matter,  but  is  simply 
a  superficial  loosening  of  the  texture  of  the  platinum,  in 
consequence  of  the  strong  heat,  whence  it  first  of  all 
appears  in  the  hottest  part  of  the  flame.  In  consequence 

K 


130  PRESERVATION    OF   PLATINUM   CRUCIBLES. 

of  the  serious  damage  which  the  gas  furnace  causes,  many 
chemists  now  discard  gas  and  ignite  platinum  crucibles 
over  specially  constructed  spirit  lamps. 

In  conjunction  with  Pettenkofer,  Erdmann  instituted 
several  experiments,  which  have  left  but  little  doubt  that 
the  phenomenon  depends  upon  a  molecular  alteration  of 
the  surface  of  the  metal.  If  a  weighed  polished  crucible 
be  ignited  for  a  long  time  over  Bunsen's  lamp,  the  position 
of  the  crucible  being  changed  from  time  to  time,  in  order 
that  the  greatest  possible  portion  of  its  surface  shall  be 
covered  with  the  grey  coating,  and  its  weight  be  then  de- 
termined anew,  it  will  be  found  that  this  has  not  increased. 
The  coating  cannot  be  removed  either  by  melting  with 
bisulphate  of  potash  or  with  carbonate  of  soda.  It  dis- 
appears, however,  when  the  metal  is  polished  with  sand  ; 
the  loss  of  weight  which  the  crucible  undergoes  being 
exceedingly  insignificant,  a  crucible  weighing  25  grammes 
having  lost  hardly  half  a  milligramme.  When  the  grey 
coating  of  the  crucible  is  examined  under  the  microscope, 
it  may  be  clearly  seen  that  the  metal  has  acquired  a  rough, 
almost  warty,  surface,  which  disappears  when  it  is  polished 
with  sand.  Platinum  wires,  which  are  frequently  ignited 
in  the  gas-flame — for  example,  the  triangles  which  are 
used  to  support  crucibles — become,  as  it  is  known,  grey 
and  brittle.  Under  the  microscope  they  exhibit  a  mul- 
titude of  fine  longitudinal  cracks,  which,  as  the  original 
superficial  alteration  penetrates  deeper,  become  more  open, 
or,  as  it  were,  spongy,  until  finally  the  wire  breaks. 

If  such  wire  is  strongly  and  perseveringly  rubbed  with 
sand,  the  cracks  disappear,  and  the  wire  becomes  smooth 
and  polished  ;  for  the  grains  of  sand,  acting  like  burnishers, 
restore  the  original  tenacity  of  the  metal,  very  little  of  its 
substance  being  rubbed  off  meanwhile.  The  loosening 
effect  of  a  strong  heat  upon  metals  is  beautifully  exhibited 
when  silver  is  ignited  in  the  gas-flame,  a  thick  polished 
sheet  of  silver  immediately  becoming  dull  white  when  thus 
heated.  Under  the  microscope  the  metal  appears  swollen 
and  warty.  Where  it  has  been  exposed  to  the  action  of 
the  inner  flame  along  its  circumference,  this  warty  con- 


CLEANING   PLATINUM   CRUCIBLES.  131 

dition  is  visible  to  the  naked  eye.  A  stroke  with  the 
burnishing  stone,  however,  presses  down  the  loosened  par- 
ticles, and  reproduces  the  original  polish.  This  peculiar 
condition  which  the  surface  of  silver  assumes  when  it  is 
ignited,  is  well  known  to  silversmiths  ;  it  cannot  be  re- 
placed by  any  etching  with  acids,  and  it  must  be  remem- 
bered that  what  is  dull  white  in  silver  appears  grey  in 
platinum. 

If  each  commencement  of  this  loosening  is  again  de- 
stroyed, the  crucibles  will  be  preserved  unaltered,  other- 
wise they  must  gradually  become  brittle.  Crucibles  of 
the  alloy  of  platinum  and  iridium  are  altered  like  those  of 
platinum,  when  they  are  ignited.  It  is,  however,  some- 
what more  difficult  to  reproduce  the  original  polish  of  the 
metal  by  means  of  sand,  as  might  be  expected,  from  the 
greater  hardness  of  the  alloy. 

The  sand  used  should  be  well  worn.  When  examined 
under  the  microscope  no  grain  of  it  should  exhibit  sharp 
edges  or  corners ;  all, the  angles  should  be  obtuse. 

If  there  are  spots  on  the  platinum  crucibles  which 
cannot  be  removed  by  the  sand  without  wearing  away  too 
much  of  the  metal,  a  little  potassium  bisulphate  is  fused 
in  the  crucible,  the  fluid  mass  shaken  about  inside,  allowed 
to  cool,  and  the  crucible  finally  boiled  with  water.  There 
are  two  ways  of  cleaning  crucibles  soiled  outside ;  either 
the  crucible  is  placed  in  a  larger  one,  and  the  interspace 
filled  with  potassium  bisulphate,  which  is  then  heated  to 
fusion,  or  the  crucible  is  placed  on  a  platinum- wire  triangle 
heated  to  redness,  and  then  sprinkled  over  with  powdered 
potassium  bisulphate.  Instead  of  the  bisulphate,  borax 
may  be  used.  Never  forget  at  last  to  polish  the  crucible 
with  sea-sand  again. 

A  remarkably  rapid  and  perfect  method  of  cleaning 
platinum  apparatus  consists  in  gently  rubbing  upon  the 
dirty  metal  a  small  lump  of  sodium-amalgam.  Sodium  has 
the  curious  property  of  lending  to  mercury  the  power  of 
'  wetting '  platinum  in  so  complete  a  manner  that  the 
positive  capillarity  between  platinum  and  an  amalgam  con- 
taining even  only  one  per  cent,  of  sodium  appears  to  be  as 


132  CLEANING    PLATINUM    CKUCIBLES. 

great  as  that  between  mercury  and  zinc,  with  this  im- 
portant difference,  however — in  the  former  case,  the 
4  wetted  '  metal  does  not  suffer  the  least  trace  of  amalga- 
mation. Even  when  foreign  metals,  such  as  lead,  tin, 
zinc,  silver,  are  purposely  added  to  the  sodium-amalgam, 
the  platinum  surface  suffers  no  disintegration. 

When  the  amalgam  has  been  rubbed  on  with  a  cloth 
until  the  whole  surface  is  brilliantly  metallic,  water  is  ap- 
plied which  oxidises  the  sodium  and  allows  the  cohesion 
of  the  mercury  to  assert  itself.  On  wiping  the  mercury 
off,  the  platinum  surface  is  left  in  admirable  condition  for 
the  burnisher. 

When  the  crucible  is  clean  it  is  placed  upon  a  clear 
platinum-wire  triangle,  ignited,  allowed  to  cool  in  the 
desiccator,  and  weighed.  This  operation,  though  not  in- 
dispensable, is  still  always  advisable,  that  the  weighing  of 
the  empty  and  the  filled  crucible  may  be  performed  under 
as  nearly  as  possible  the  same  circumstances. 

In  using  platinum  crucibles,  it  must  be  remembered 
that  certain  substances  must  not  be  ignited  in  them. 
Berzelius  says  that  '  it  is  improper  to  ignite  in  platinum 
vessels  the  caustic  alkalies  or  the  nitrates  of  any  alkaline 
base,  such  as  lime,  baryta,  or  strontia,  because  the  affinity 
of  the  alkali  for  platinum  oxide  causes  a  very  considerable 
oxidation  of  the  metal ;  and  after  the  saline  matter  is  re- 
moved, the  surface  of  the  metal  is  found  to  be  honey- 
combed.' 

The  alkaline  sulphides  or  the  alkaline  sulphates  mixed 
with  charcoal  are  inadmissible,  because  the  sulphides  so 
formed  attack  platinum  even  more  energetically  than  the 
caustic  alkalies  ;  so  are  metals  whose  fusing-point  is  lower 
than  that  of  platinum,  because  an  alloy  would  be  formed. 
Gold,  silver,  and  copper  may  be  heated  to  dull  redness  in 
platinum  vessels  without  danger  ;  but  fused  lead  cannot 
come  in  contact  with  platinum  without  destroying  it. 
A  drop  of  fused  lead,  tin,  zinc,  or  bismuth,  placed  on 
red-hot  platinum,  always  produces  a  hole.  Neither  can 
a  phosphide  or  phosphoric  acid  mixed  with  charcoal 
be  ignited  in  vessels  of  platinum,  because  a  platinum 


SILVER  CRUCIBLES — CUPELS.  133 

phosphide  is  produced,  which  is  an  exceedingly  brittle 
compound. 

In  analyses  by  the  humid  method,  nitro-hydrochloric 
acid  (aqua  regia\  even  when  very  dilute,  must  not  be 
allowed  to  come  in  contact  with  platinum,  and,  as  a 
general  rule,  liquids  containing  either  free  chlorine,  bro- 
mine, or  iodine  must  not  be  boiled  in  platinum  capsules. 

SILVEE  CRUCIBLES  can  only  be  used  at  temperatures 
below  full  redness.  They  are  not  affected  by  caustic 
alkalies,  but  must  not  come  in  contact  with  sulphur  or  be 
heated  over  coke,  coal,  gas,  or  other  fuel  containing 
sulphur. 

CUPELS. — These  are  vessels  in  which  the  operation 
termed  cupellation  is  carried  on.  They  must  be  made  of 
such  substances  as  are  not  acted  upon  by  certain  fused 
oxides,  as  those  of  lead  or  bismuth,  and  their  texture  has 
to  be  sufficiently  loose  to  allow  of  the  oxides  penetrating 
their  substance  readily,  and  yet  be  sufficiently  strong  to 
bear  handling  without  breaking. 

There  are  several  substances  of  which  cupels  might  be 
made,  which  will  fulfil  all  these  conditions,  but  only  one 
is  in  general  use,  viz.  the  ash  of  burnt  bones.  This  consists 
principally  of  calcium  phosphate,  with  a  little  calcium  car- 
bonate and  fluoride.  Berzelius  found  that  bones  of  oxen 
contained  57  parts  of  calcium  phosphate  for  every  3'8 
parts  of  calcium  carbonate,  whilst,  according  to  Barros, 
sheep  bones  contain  80  parts  of  calcium  phosphate  to  19 
parts  of  calcium  carbonate.  When  bones  are  burnt  whole 
they  likewise  contain  mineral  matter  derived  from  the 
cartilage,  such  as  alkaline  sulphates  and  carbonates.  The 
greater  part  of  the  calcium  carbonate  is  likewise  converted 
into  caustic  lime. 

The  bones  of  sheep  and  horses  are  best  for  cupels.  In 
getting  rid  of  the  organic  matter,  it  is  advisable  to  boil 
them  repeatedly  in  water  before  burning  them.  This  dis- 
solves a  great  part  of  the  organic  matter.  If  the  bones 
are  not  rendered  quite  white  by  the  first  ignition,  but  con- 
tain a  little  carbon,  they  should  be  ground  up,  moulded 
into  shape,  and  burned  again. 


134  MANUFACTURE   OF   CUPELS. 

Care  should  be  taken  not  to  heat  the  bone  earth  too 
strongly.  In  this  case  the  bones  will  have  a  smooth,  glassy 
fracture,  and  will  not  be  sufficiently  spongy  or  absorbent 
to  make  good  cupels. 

When  the  bones  are  burnt  white  throughout,  they  must 
be  finely  ground,  sifted,  and  washed  several  times  with 
boiling  distilled  water  till  all  soluble  salts  are  removed. 
The  finest  particles  of  the  powdered  bone  earth  will  remain 
longest  suspended  in  the  washing  waters.  This  must  be 
allowed  to  settle  separately,  and  should  be  reserved  for 
giving  a  final  coating  to  the  surface  of  the  cupels ;  this 
coating  acts,  to  a  certain  extent,  like  a  fine  filter,  and  may 
be  applied  to  all  cupels,  although  the  body  of  the  cupel  is 
made  of  different  materials. 

For  the  body  of  the  cupels,  the  bone-ash  should  be 
about  as  fine  as  wheat  flour.  If  too  coarse,  litharge  con- 
taining silver  will  be  absorbed  into  its  pores,  and  will  occa- 
sion a  loss  of  silver. 

Cupels  must  neither  crack  nor  alter  in  texture  at  a 
white  heat.  It  is  very  important  that  they  should  not 
contain  carbon,  and  therefore,  in  making  them,  the  bone 
earth  must  not,  as  sometimes  recommended,  be  mixed  with 
beer,  or  water  containing  adhesive  substances.  Nothing 
but  pure  water  should  be  used,  and  the  mixture  should  be 
just  sufficiently  moist  to  adhere  strongly  when  well  pressed, 
but  not  so  moistj  as  to  adhere  to  the  finger  or  the  mould 
employed  to  fashion  the  cupels.  The  mould  (fig.  63)  con- 
.  63.  sists  of  three  pieces  :  one  a  ring,  6,  having  a 
conical  opening ;  another  a  pestle,  «,  having 
a  hemispherical  end  fitting  the  larger  opening 
of  the  ring  ;  and  the  third,  c,  a  piece  of  turned 
metal,  into  which  b  fits  ;  c  serves  to  form  an 
even  bottom  to  the  cupel.  In  order  to  mould 
the  cupels,  proceed  as  follows  :  Place  the  ring 
on  the  lower  piece  c,  and  fill  it  with  the  com- 
position ;  then  place  the  pestle  upon  it,  and 
force  it  down  as  much  as  possible  :  by  this  means  the 
moistened  bone  ash  will  become  hardened,  and  take  the 


MANUFACTURE    OF    CUPELS.  135 

form  of  the  pestle  ;  the  latter  must  then  be  driven  as 
much  as  possible  by  repeated  blows  from  a  hammer, 
until  quite  home.  The  surface  of  the  cupel  may  then 
have  sifted  over  it  a  little  of  the  very  fine  levigated  bone- 
ash,  and  the  pestle  hammered  again  on  it.  It  is  then  to 
be  turned  lightly  round,  so  as  to  smooth  the  inner  sur- 
face of  the  cupel,  and  withdrawn  :  the  cupel  is  removed 
from  the  mould  by  a  gentle  pressure  on  the  narrowest  end. 
When  in  this  state,  the  cupel  must  be  dried  gently  by  a 
stove  ;  and  lastly,  ignited  in  a  muffle,  to  expel  all  moisture. 
It  is  then  ready  for  use. 

There  are  two  or  three  points  to  attend  to  in  manufac- 
turing the  best  cupels.  First,  the  powdered  bone-ash  must 
be  of  a  certain  degree  of  fineness  ;  secondly,  the  paste  must 
be  neither  too  soft  nor  too  dry ;  and  thirdly,  the  pressure 
must  be  made  with  a  certain  degree  of  force.  A  coarse 
powder,  only  slightly  moistened  and  compressed,  furnishes 
cupels  which  are  very  porous,  break  on  the  least  pressure, 
and,  as  before  mentioned,  allow  small  globules  of  metal  to 
enter  into  their  pores. 

When,  on  the  contrary,  the  powder  is  very  fine,  the 
paste  moist,  and  compressed  strongly,  the  cupels  have 
much  solidity,  and  are  less  porous  ;  the  fine  metal  cannot 
penetrate  them,  but  the  operation  proceeds  very  slowly  : 
besides,  the  assay  is  likely  to  become  dulled,  and  incapable 
of  proceeding  without  a  much  higher  degree  of  tempera- 
ture being  employed. 

Cupels  for  assaying  silver  bullion  are  sometimes  made 
of  equal  parts  of  bone-ash  and  beechwood-ash ;  and  for 
assaying  gold.  2  parts  of  beechwood-ash  and  1  part  of 
bone-ash  are  used.  The  hemispherical  cavity  of  both 
these  kinds  are  coated  with  the  fine  levigated  powder  of 
bone-ash. 

Beechwood-ash  is  preferred  for  the  manufacture  of 
cupels  on  account  of  the  larger  proportion  of  phosphoric 
acid  it  contains. 

According  to  Hertwig,  beechwood-ash  contains  in  100 
parts : — 


136 


PYROMETRY. 


Potassium  carbonate 
Sodium  carbonate 
Potassium  sulphate 
Calcium  carbonate 
Magnesium  carbonate 
Calcium  phosphate 
Magnesium       „ 
Iron  „ 

Aluminium  „ 
Manganese  „ 
Silica 


1172 
12-37 
3-49 
49-54 
779 
3-32 
2-92 
0-76 
1-51 
1-59 
2-46 


SCORIFIERS. — A  scorifier  (fig.  64)  is  a  vessel  made  much 
in  the  shape  of  a  cupel,  but  of  crucible  earth.  The  proper 
use  both  of  cupels  and  scorifiers  will  be  explained  under 
the  head  of  silver-assaying. 

METHODS  OF  MEASURING  THE  HEAT  OF  FURNACES. — As 
much  of  the  accuracy  of  an  assay  depends  on  the  tempera- 
ture at  which  it  is  made,  and  as  the  temperature  required 


FIG.  64. 


varies  with  each  metal,  it  is  very  desirable  to  possess  some 
means  of  ascertaining  the  heat  of  the  furnace  more  accu- 
rately than  by  the  eye.  Many  persons  have  devised 
instruments,  called  pyrometers,  for  this  purpose ;  the 
earliest  being  those  of  Mr.  Wedgwood  and  the  late  Pro- 
fessor Daniel,  of  King's  College. 

We  shall  not  give  a  description  of  Wedgwood's  pyro- 
meter, as  its  indications  are  inaccurate,  from  the  fact  that 
the  clay  cylinders,  whose  contraction  serves  to  measure 
the  temperature,  will  contract  as  much  by  the  long  con- 
tinuance of  a  low  heat  as  by  the  short  continuance  of  a 
high  one.  Hence  the  degrees  of  heat  measured  by  Wedg- 


DANIELS   PYROMETER. 


137 


wood's  pyrometer  have  been  enormously  exaggerated.  It 
was  long  since  noticed  that  it  did  not  produce  comparable 
effects  ;  and  this  was  supposed  to  proceed  wholly  from 
the  impossibility  of  obtaining  clay  perfectly  alike  for  each 
experiment. 

Daniel's  pyrometer  is  composed  of  a  rod  of  platinum 
simply  laid  in  a  groove  made  of  refractory  clay,  and  baked 
in  the  highest  degree  of  heat.  This  rod  rests  at  one  end 
on  the  edge  which  terminates  the  groove,  and  at  the  other 
on  a  lever  with  two  arms,  the  larger  of  which  forms  a 
needle  on  a  graduated  arc  of  a  circle  ;  so  that  the  removal 

FIG.  65. 


of  this  needle  from  its  position  marks  the  additional  length 
which  the  metal  acquires  by  the  heat.  The  following  is 
Daniel's  description  of  his  pyrometer :  '  It  consists  of  two 
parts  (see  fig.  65),  which  may  be  distinguished  as  the 
register  and  the  scale.  The  register  is  a  solid  bar  of  black- 
lead  or  earthenware  highly  baked.  In  this  a  hole  is  drilled, 
into  which  a  bar  of  any  metal,  «,  six  inches  long,  may  be 
dropped,  and  which  will  then  rest  upon  its  solid  end.  A 
cylindrical  piece  of  porcelain,  &,  called  the  index,  is  then 
placed  upon  the  top  of  the  bar,  and  confined  in  its  place 
by  a  ring  or  strap  of  platinum  passing  round  the  top  of  the 
register,  which  is  partly  cut  away  at  the  top,  and  tightened 


138  DANIEL'S  PYROMETER. 

by  a  wedge  of  porcelain.  When  such  an  arrangement  is 
exposed  to  a  high  temperature,  it  is  obvious  that  the  ex- 
pansion of  the  metallic  bar  will  force  the  index  forward  to 
the  amount  of  the  excess  of  its  expansion  over  that  of  the 
black-lead,  and  that  when  again  cooled  it  will  be  left  at  the 
point  of  greatest  elongation.  What  is  now  required  is  the 
measurement  of  the  distance  which  the  index  has  been 
thrust  forward  from  its  first  position,  and  this,  though  in 
any  case  but  small,  may  be  effected  with  great  precision 
by  means  of  the  scale,  c.9  * 

This  is  independent  of  the  register,  and  consists  of  two 
rules  of  brass  accurately  joined  together  at  a  right  angle 
by  their  edges,  and  fitting  square  upon  the  two  sides  of  the 
black-lead  bar.     At  one  end  of  this  double  rule  a  small 
plate  of  brass  projects  at  a  right  angle,  which  may  be 
brought  down  upon  the  shoulder  of  the  register  formed  by 
the  notch  cut  away  for  the  reception  of  the  index.     A 
movable  arm  is  attached  to  this  frame,  turning  at  its  fixed 
extremity  on  a  centre,  and  at  its  other  carrying  the  arc  of 
a  circle,  whose  radius  is  exactly  five  inches,  accurately 
divided  into  degrees,  and  thirds  of  a  degree.     Upon  this 
arm,  at  the  centre  of  the  circle,  another  lighter  arm  is  made 
to  turn,  one  end  of  which  carries  a  nonius  with  it,  which 
moves  upon  the  face  of  the  arc,  and  subdivides  the  former 
graduation  into  minutes  of  a  degree  ;  the  other  end  crosses 
the  centre,  and  terminates  in  an  obtuse  steel  point,  turned 
inwards  at  a  right  angle.     When  an  observation  is  to  be 
made,  a  bar  of  platinum  or  malleable  iron  is  placed  in  the 
cavity  of  the  register  ;  the  index  is  to  be  pressed  down  upon 
it,  and  firmly  fixed  in  its  place  by  the  platinum  strap  and 
porcelain  wedge.     The  scale  is  then  to  be  applied  by  care- 
fully adjusting  the  brass  rule  to  the  sides  of  the  register, 
and  fixing  it  by  pressing  the  cross  piece  upon  the  shoulder, 
and  placing  the  movable  arm  so  that  the  steel  part  of  the 
radius  may  drop  into  a  small  cavity  made  for  its  reception, 
and  coinciding  with  the  axis  of  the  metallic  bar.  The  minute 
of  the  degree  must  then  be  noted  which  the  nonius  indicates 
upon  the  arc.     A  similar  observation  must  be  made  after 

*  Daniel's  '  Chemical  Philosophy,'  p.  111. 


DANIELS   PYROMETER. 


139 


the  register  has  been  exposed  to  the  increased  temperature 
which  it  is  designed  to  measure,  and  again  cooled,  and  it 
will  be  found  that  the  nonius  has  been  moved  forward  a 
certain  number  of  degrees  or  minutes.  The  scale  of  this 
pyrometer  is  readily  connected  with  that  of  the  thermometer 
by  immersing  the  register  in  boiling  mercury,  whose  tem- 
perature is  as  constant  as  that  of  boiling  water,  and  has 
been  accurately  determined  by  the  thermometer.  The 
amount  of  expansion  for  a  known  number  of  degrees  is 
thus  determined,  and  the  value  of  all  other  expansions  may 
be  considered  as  proportionate. 

By  Daniel's  pyrometer  the  melting  point  of  cast  iron 
has  been  ascertained  to  be  2,786°,  and  the  highest  tem- 
perature of  a  good  wind  furnace  3,300°  Fahrenheit — points 
which  were  estimated  by  Mr.  Wedgwood  at  17,977°  and 
21,877°  respectively. 

The  following  is  a  list  of  the  melting  points  of  some  of 
the  metals  as  ascertained  by  Professor  Daniel ;  and  it  is 
obvious  that  in  an  assay  of  each  particular  metal  the  tem- 
perature employed  must  exceed  by  a  considerable  number 
of  degrees  its  melting  point.  The  table  is,  therefore,  very 
useful. 

Fahr. 

422° 
442 
497 
612 


Tin  melts  at 
Cadmium 
Bismuth 
Lead    . 
Zinc      . 
Silver  . 

gar. 

Cast  iron 

Cobalt  and  nickel  rather  less  fusible  than  iron. 


773 

1860 
1996 
2016 
2786 


Mr.  S.  Wilson*  has  described  an  ingenious  process  of 
measuring  high  temperatures.  He  exposes  a  given  weight 
of  platinum  or  Stourbridge  clay  to  the  action  of  the  heat 
which  is  to  be  measured,  and  then  quenches  it  in  a  definite 
weight  of  water  at  a  certain  temperature.  Thus,  if  the 
piece  of  platinum  weigh  1,000  grains  and  the  water  2,000 
grains  at  60°  F.,  and  should  the  heated  platinum  when 
dropped  into  the  water  raise  its  temperature  to  90°,  then, 

*  '  Philosophical  Magazine/  ser.  iv.  vol.  iv.  p.  157. 


140 


COMPARISON    OF    HIGH   TEMPERATURES. 


FIG.  66. 


90° -60°=  30°  ;  which,  multiplied  by  2  (because  the  weight 
of  the  water  is  twice  that  of  the  platinum),  gives  60° — 
the  temperature  to  which  a  weight  of  water  equal  to  the 
platinum  would  have  been  raised.  To  convert  this  into 
Fahrenheit  degrees  we  must  multiply  by  31^,  which  is  the 
specific  heat  of  water  as  compared  with  platinum,  that  of 
the  latter  being  1.  Therefore,  60°  x  31|=1875°,  which 
will  be  the  temperature  of  the  furnace. 

One  or  two  other  methods  of  measuring  high  tempera- 
tures applicable  to  special  cases  may  here  be  mentioned. 

Mr.  C.  W.  Siemens,  C.E.,  F.E.S.,  has  invented  an  inge- 
nious pyrometer,  the  principle  of  which  is,  that  as  the 
electrical  conductivity  of  platinum,  iron,  and 
other  metals  decreases  as  they  rise  in  tem- 
perature, their  increase  of  resistance  to  the 
passage  of  the  current  is  a  measure  of  the  heat 
to  which  the  metals  are  subjected. 

The  principle  of  construction  may  be  ex- 
plained by  the  aid  of  fig.  66,  in  which  FAB 
is  a  tube  of  pipe-clay,  and  the  length  between 
the  projections,  A  and  B,  has  a  screw-shaped 
spiral  groove  cut  on  its  outer  surface  ;  the 
length  of  this  part  of  the  tube  is  about  3  inches. 
A  spiral  of  fine  platinum  wire  lies  in  the  groove, 
each  turn  of  the  platinum  spiral  being  thus  pro- 
tected from  lying  in  contact  with  its  neighbour 
by  the  projecting  edges  of  the  groove,  by  which 
plan  of  insulation  the  current  is  forced  to  pass 
through  the  whole  length  of  the  fine  wire.  D 
is  a  little  platinum  clam,  connected  with  one 
pole  of  the  battery,  and  the  position  of  this 
clam  on  the  spiral  regulates  the  length  of  pla- 
tinum wire  through  which  the  current  shall 
pass.  By  this  plan  of  adjustment,  all  the  py- 
rometers constructed  by  Mr.  Siemens  are  made 
to  agree  with  each  other. 

At  F>  the  ends  of  the  thin  platinum  wire  are  connected 
with  very  thick  platinum  wire,  and  higher  up,  near  E, 
where  the  heat  of  the  furnace  is  less  felt,  the  thick  platinum 


E 

K 

F 

' 

r 

R 

I' 

~5T 

R 

A* 

COMPARISON   OF   HIGH   TEMPERATURES.  141 

wires  are  connected  with  thick  copper  wires,  shown  at  P ; 
from  E  to  F,  these  connecting  wires  are  protected  by  clay 
pipes,  as  shown  in  the  cut. 

When  this  arrangement  has  to  be  used,  the  whole  of  it 
is  dropped  into  a  thick  metal  pipe  made  of  iron,  copper,  or 
platinum,  according  to  the  heat  of  the  furnace  to  be  tested. 
The  lower  end  of  this  outer  pipe  is  shown  at  K  M,  and  when 
it  is  used  the  spiral,  A  B,  lies  inside  it  at  x  M.  At  R  there  is 
a  very  thick  collar  of  metal  in  which  the  heat  accumulates, 
and  this  prevents  the  cooling  action  of  the  length  K  R  (most 
of  which  does  not  enter  the  furnace)  from  interfering  with 
the  accuracy  of  the  indications.  The  ends  of  the  wires,  P, 
are  connected  with  suitable  and  very  delicate  electrical 
apparatus,  by  which  the  increasing  electrical  resistance  of 
the  hot  spiral  is  measured. 

A  good  plan  for  comparing  the  temperatures  of  two  fur- 
naces is  to  prepare  alloys  of  platinum  and  gold,  containing 
definite  quantities,  say,  5, 10,  15,  20  per  cent.  &c.,  of  gold. 
These  fuse  at  intermediate  temperatures  between  gold  and 
platinum.  By  placing  small  angular  chips  of  these  alloys 
separately  in  muffles,  and  noticing  which  are  melted,  which 
softened  only,  and  which  resist  the  action  of  the  heat,  an 
idea  of  the  power  of  the  furnace  is  obtained.  In  this  way 
the  amount  of  heat  required  to  perform  any  operation 
may  be  registered  for  future  reference,  by  simply  recording 
that  it  was  sufficient  just  to  melt,  say,  a  20  gold  80  pla- 
tinum allov. 


142 


CHAPTEE  V. 

FUEL:     ITS   ASSAY   AND   ANALYSIS. 

BEFORE  treating  of  the  assay  of  metals  and  metalliferous 
ores,  it  is  advisable  to  devote  some  space  to  the  important 
subject  of  fuel.  The  substances  employed  as  fuel,  although 
all  of  vegetable  origin,  are  derived  either  from  the  vege- 
table kingdom  (wood),  or  from  the  mineral  kingdom  (peat, 
brown  coal,  coal,  anthracite).  These  natural  fuels  can 
be  converted  into  artificial  fuels  by  heating  them  more 
or  less  out  of  contact  with  the  air  (charcoal,  turf-charcoal, 
coke). 

The  essential  elements  of  combustible  matters  are  car- 
bon, oxygen,  and  hydrogen  ;  nitrogen  being  present  some- 
times, but  only  in  small  proportions.  These  constitute  the 
organic  part ;  various  salts  and  silica  constitute  the  inor- 
ganic part,  or  ash.  The  valuable  constituents  of  fuel,  on 
which  its  calorific  and  reducing  powers  depend,  are  the 
carbon  and  hydrogen,  and  it  is  upon  the  combustion  or 
union  of  these  elements  with  oxygen  to  form  carbonic 
acid  and  water,  that  the  heating  effect  of  the  fuel  depends. 

The  more  oxygen  a  fuel  contains,  the  less  carbon  and 
combustible  gases  it  will  yield,  and  the  more  hydrogen, 
the  more  combustible  gases. 

The  proportion  of  hydrogen  to  oxygen  in  wood        .  is     1  :  7 

»  »  v  "  turf          .  ,,1:6 

„  „  „  fossil-wood  „    1:4 

„  „  „  coal  .  „     1  :  2-3 

„  „  „  anthracite  „     1:1 

The  more  oxygen,  the  less  carbon  the  fuel  contains, 
thus : — 

Anthracite  contains  about  90  per  cent,  carbon 
Coal  „  „     80      „  „ 

Brown  coal       „  „     70      „  „ 

Fossil-wood  and  turf     „     60      „  „ 

Wood  „  „     50      „ 


ASSAY   OF   FUEL.  143 

The  more  carbon  a  fuel  contains,  the  greater  heat  it  pro- 
duces, and  the  more  difficult  it  is  to  ignite. 

The  greater  the  amount  of  hydrogen  in  a  fuel,  the 
more  inflammable  it  will  be,  and  the  larger  flame  it  gives, 
the  hydrogen  being  evolved  below  a  red  heat.  But  the 
more  carbon  present,  the  less  flame.  These  differences 
are  shown  in  a  blazing  fire  and  a  glowing  fire.  In  a  flame 
the  hottest  part  is  at  the  periphery,  whilst  in  a  glowing 
fire  the  greatest  heat  is  in  the  immediate  contact  of  the 
burning  surface. 

An  elementary  analysis  of  coal  teaches  little  with 
regard  to  the  nature  or  practical  value  of  the  combustible. 
A  proximate  analysis,  on  the  contrary,  enables  us  to  learn 
something  in  regard  to  the  real  nature  of  the  coal.  The 
moisture  and  ash  are  not  only  diluents  of  the  fuel,  but 
are  in  themselves  obstacles  to  its  effectiveness ;  the  vapo- 
risation of  the  moisture  causes  a  serious  loss  of  heat,  whilst 
the  ashes,  by  hindering  complete  combustion  and  by  the 
heat  they  contain  when  dropped  through  the  grate,  con- 
stitute another  loss.  By  furthermore  determining  the 
total  amount  of  volatile  matter  we  learn  both  the  per- 
centage of  coke  in  the  fuel  and  the  amount  of  carbon 
(fixed  combustible)  and  bitumen  (volatile  combustible 
matter).  Although  neither  of  these  two  products  can 
be  considered  as  simple  chemical  compounds,  it  is  never- 
theless of  the  utmost  practical  importance  to  know  these 
two  quantities,  because  of  the  great  value  of  coke  and  gas 
in  manufactures. 

The  assay  of  fuel  comprises  the  following  examinations : 

1.  The  examination  of  the  external  appearance  of  the 
fuel,  its  porosity  or  compactness,  its  fracture,  the  size  and 
shape  of  the  pieces  composing  it. 

2.  Determination  of  the  adhering  water. 

3.  Determination  of  the  specific  gravity. 

4.  Determination  of  the  absolute  heating  power. 

5.  Determination  of  the  specific  heating  power. 

6.  Determination  of  the  pyrometric  heating  power. 

7.  Determination  of  the  volatile  products  of  carbonisa- 
tion. 


144  ASSAY   OF    FUEL. 

8.  Examination  of  the  coke  or  charcoal  left  behind  on 
carbonisation,  both  with  regard  to  quality  and  quantity. 

9.  Determination  of  the  amount  of  ash,  and  its  compo- 
sition. 

10.  Determination  of  the  amount  of  sulphur. 

11.  Examination  of  any  other  peculiarity  which  may 
be  noticed  during  the  burning  or  carbonisation  of  the  fuel. 

1.  EXTERNAL  APPEARANCE  OF  THE  FUEL,  ITS  POROSITY, 
COMPACTNESS,  FRACTURE,  SIZE,  AND  SHAPE  OP  PIECES. — From 
the  outward  appearance  of  a  fuel,  its  cleavage,  and  an 
examination  of  the  embedded  earthy  matter,  iron  pyrites, 
gypsum,  &c.,  its  applicability  to  any  special  purpose  may 
be  judged.  Its  degree  of  inflammability,  together  with 
the  pressure  of  blast  which  it  will  bear  in  the  furnace, 
partly  depend  on  the  more  or  less  compactness  of  the  fuel. 
The  amount  of  loss  which  it  will  suffer  in  transport  de- 
pends upon  its  friability.  Playfair  and  De  la  Beche  * 
determined  the  amount  of  this  loss  in  coal  by  rotating 
in  a  barrel  different  qualities  of  coal  for  the  same  time. 
The  powder  produced  was  separated  and  weighed,  and  in 
this  way  the  friability  or  cohesion  of  a  fuel  could  be  ex- 
pressed in  percentages.  Schrotterf  made  the  same  experi- 
ments with  brown  coal. 

The  size  and  form  of  the  pieces  composing  the  fuel  is 
important,  as  on  this  depends  the  space  occupied  in  its 
stowage — an  important  point  for  steam- vessels.  This 
space  cannot  be  calculated  from  its  specific  gravity,  but 
must  be  ascertained  by  direct  measurement.  The  space 
occupied  will  be  smallest  when  the  form  of  the  lumps  is 
cubical.  Playfair  and  De  la  Beche  have  also  investigated 
this  subject. 

2.  DETERMINATION  OF  THE  ADHERING  WATER. — The  water 
contained  in  a  fuel  exerts  great  influence  on  its  heating 
power.  It  not  only  increases  its  bulk,  but  it  acts  in- 
juriously by  abstracting  a  certain  quantity  of  heat  required 
for  its  evaporation,  and  it  also  causes  imperfect  combus- 

*  Dingl.  ex.  212,  262 ;  cxiv.  346.  Liebig's  <  Jahresber.,'  1847-1848,  p. 
1117  ;  1849,  p.  708. 

f  Wien.  Akad.  Ber.  1849,  Nov.  and  Dec.  p.  240.  Liebig's  '  Jahresber.' 
1849,  p.  709. 


ASSAY    OF   FUEL.  145 

tion.  For  this  reason,  wood,  turf,  and  brown  coal  never 
give  so  high  a  temperature  as  coal,  anthracite,  and  coke. 

The  determination  of  the  adhering  water  is  effected  by 
drying  a  certain  weight  of  the  pounded  fuel  in  a  water- 
bath  at  212°  F.,  or  in  an  air-bath  at  220°.  It  may  also  be 
ascertained  by  placing  a  certain  weight  of  the  powdered 
fuel  in  a  glass  tube,  heating  to  212°,  and  passing  over  it 
air  dried  by  means  of  chloride  of  calcium,  till  the  fuel  no 
longer  loses  weight.  The  amount  of  water  which  the 
dried  fuel  will  absorb  from  the  atmosphere  in  twenty-four 
hours  should  also  be  determined,  in  order  to  ascertain  its 
hygroscopic  qualities. 

3.  DETERMINATION  OF  THE  SPECIFIC  GRAVITY. — The  specific 
gravity  of  a  fuel  depends  on  its  density  and  the  amount 
of  ash,  and  it  appears  also  to  be  in  proportion  to  its  greater 
or  less  inflammability.  Of  two  equal  volumes  of  carbonised 
fuel,  the  one  will  produce  the  greatest  heating  effect  which 
has  the  greatest  specific  gravity,  provided  the  density  is 
not  produced  by  mineral  constituents. 

The  determination  of  the  specific  gravity  is  difficult, 
and  sometimes  uncertain,  owing  to  the  cleavage  of  the 
fuel,  and  the  entanglement  of  air  in  its  pores.  The  best 
way  of  obviating  this  difficulty  is  as  follows  : — 

Coarse  fragments,  freed  by  means  of  a  sieve  from  all 
small  particles,  and  averaging  1-1  Oth  c.c.  in  volume,  are 
introduced  into  a  fifty-gramme  flask  provided  with  a 
thermometer  stopper.  The  constants  for  this  flask  for 
temperatures  varying  from  50°  to  80°  F.  are  previously 
carefully  determined. 

The  given  sp.  gr.  corresponds  to  the  coal  perfectly 
soaked,  so  that  all  its  pores  are  filled  with  water.  That 
requires,  on  the  average,  12  hours,  permitting  two  de- 
terminations per  day,  one  in  the  morning,  another  in  the 
evening. 

That  this  precaution  is  important  may  be  seen  from 
the  following  example  :  2760  grms.  coal  gave  the  sp.  gr. 
1-309  at  64°  F.,  immediately  after  filling  the  flask  with 
water:  after  about  12  hours'  soaking,  the  sp.  gr.  had 
increased  to  1-328,  for  the  same  temperature.  According 

L 


146  ASSAY   OF   FUEL. 

to  this  latter  determination,  a  cubic  foot  of  this  coal  would 
weigh  82'76  Ibs. ;  according  to  the  former,  only  81-58,  or 
1-18  Ibs.  less.  This  shows  a  considerable  degree  of  po- 
rosity of  the  coal,  and  indicates  the  absurdity  of  giving 
the  weight  in  pounds  of  a  cubic  foot  of  coal  with  four 
decimals,  although  no  statement  in  regard  to  temperature 
or  time  of  weighing  is  made. 

4.  DETERMINATION  OF  THE  ABSOLUTE  HEATING  POWER  — 
The  value  of  a  fuel  for  any  purpose  depends  chiefly  on 
its  price  and  the  quantity  required  for  that  purpose.  The 
quantity  required  depends  on  the  heating  power  possessed 
by  a  certain  weight  of  fuel  (its  absolute  heating  power)  or 
that  possessed  by  a  certain  volume  (its  specific  heating 
power). 

The  less  oxygen,  ash,  and  water  the  fuel  contains,  the 
greater  its  heating  power  will  be,  and  this  will  also  increase 
in  proportion  to  the  carbon  and  hydrogen  present. 

Whether  the  combustion  is  effected  quickly  or  slowly, 
the  amount  of  heat  produced  will  be  the  same,  but  the 
degree  of  temperature  attained  will  be  very  difficult.  This 
latter  constitutes  the  pyrometric  heating  power. 

The  determination  of  the  absolute  heating  powder  of  a 
fuel  may  be  effected — 

a.  By  heating  a  definite  quantity  of  water  from  32°  F. 
to  212°  ; 

b.  By  ascertaining  how  much  fuel  is  required  to  melt 
a  known  weight  of  ice  ; 

c.  By  ascertaining  how  much  water  may  be  evaporated 
by  1  Ib.  of  different  kinds  of  fuel ; 

d.  By  ascertaining  how  much  the  temperature  of  a 
room  increases  by  burning  a  certain  weight  of  a  fuel  in 
a  stove. 

e.  By  ascertaining  the  elementary  composition  of  the 
fuel,  and  calculating  how  much  oxygen  will  be  required 
to  convert  the  carbon  and  hydrogen  into  carbonic  acid 
and  water ;  the  quantity  of  heat  produced  will  be  in  pro- 
portion to  the  amount  of  oxygen  consumed. 

/.   By  Berthier's  method. 
(j.  By  Dr.  lire's  method. 


BERTHIER'S  METHOD  FOE  ASSAY  OF  FUEL.  147 

According  to  Berthier,  the  most  convenient  method 
for  ascertaining  the  comparative  calorific  power  of  any 
combustible  matter  is  by  means  of  litharge.  He  says :  It 
has  been  proved  by  the  experiments  of  many  philosophers 
that  the  quantities  of  heat  emitted  by  combustible  sub- 
stances are  exactly  proportioned  to  the  amounts  of  oxygen 
required  for  their  complete  combustion.  Whence,  after 
the  elementary  constitution  of  any  combustible  is  known, 
its  calorific  power  is  easily  determined  by  calculation. 
.For  instance,  it  is  only  necessary  to  ascertain  the  quantity 
of  oxygen  absorbed  in  the  conversion  of  all  its  carbon 
into  carbonic  acid,  and  all  its  hydrogen  into  water,  and 
compare  that  quantity  with  that  which  is  consumed  in 
burning  a  fuel  whose  calorific  power  is  well  ascertained. 
Such  a  fuel  is  pure  charcoal. 

By  adopting  the  principle  just  pointed  out,  it  may  be 
conceived  that,  without  knowing  the  composition  of  a 
fuel,  its  heating  power  may  be  ascertained  by  determining 
the  amount  of  oxygen  it  absorbs  in  burning.  This  can  be 
done  in  a  very  simple  and  expeditious  manner,  if  not 
exactly,  at  least  with  sufficient  exactitude  to  afford  very 
useful  results  in  practice.  It  is  as  follows  :  many  metallic 
oxides  are  reduced  with  such  facility  that  when  heated 
with  a  combustible  body,  the  latter  burns  completely, 
without  any  of  its  elements  escaping  the  action  of  the 
oxygen  of  the  oxide,  if  the  operation  be  suitably  per- 
formed. The  composition  of  the  oxide  being  well  known,  if 
the  weight  of  the  part  reduced  to  the  metallic  state  be  taken, 
the  quantity  of  oxygen  employed  in  the  combustion  can 
be  ascertained.  In  order  to  collect  the  metal  and  separate 
it  from  the  non-reduced  mass,  it  must  be  fusible  as  well  as 
its  oxide.  Litharge  fulfils  these  conditions,  and  experi- 
ment has  proved  that  it  completely  burns  the  greater  part 
of  all  ordinary  fuels ;  the  only  exceptions  are  some  very 
bituminous  matters  containing  a  large  proportion  of  vola- 
tile elements,  a  portion  of  which  escapes  before  the  tem- 
perature is  sufficiently  high  to  allow  the  reduction  to  take 
place.  The  experiment  is  made  as  follows  :  10  grains  of 
the  finely  powdered  or  otherwise  divided  fuel  is  mixed 

L  2 


148  BERTHIEK'S  METHOD  FOK  ASSAY  OF  FUEL. 

with  about  400  grains  of  litharge.  The  mixture  is  care- 
fully placed  in  an  earthen  crucible,  and  covered  with  200 
grains  more  litharge.  The  crucible  is  then  placed  in  the 
fire  and  gradually  heated.  When  the  fusion  is  perfect,  the 
heat  is  urged  for  about  ten  minutes,  in  order  that  all  the 
lead  may  collect  into  a  single  button.  The  crucible  is 
then  taken  from  the  fire,  cooled,  broken,  and  the  button 
of  lead  weighed.  Sometimes  the  button  is  livid,  leafy, 
and  only  slightly  ductile  ;  in  which  case  it  has  absorbed 
a  little  litharge.  This  can  be  partially  prevented  by  fusing 
slowly,  and  adding  a  little  borax. 

Two  assays,  at  least,  ought  to  be  made,  and  those  re- 
sults which  differ  more  than  a  grain  or  two  ought  not  to 
be  relied  on.  The  purer  the  litharge,  the  better  the  re- 
sult ;  it  ought  to  contain  as  little  minium  as  possible.  It 
is.  an  excellent  plan  to  mix  up  the  litharge  of  commerce 
with  one  or  two  thousandths  of  its  weight  of  charcoal,  and 
fuse  the  whole  in  a  pot ;  when  cold,  pulverise  the  litharge, 
which  will  now  be  deprived  of  minium. 
:,:..  Pure  carbon  produces,  with  pure  litharge,  thirty-four 
times  its  weight  of  lead,  whilst  hydrogen  gives  103'7  times 
its,  weight  of  lead  ;  that  is  to  say,  a  little  more  than  three 
times  as  much, as  .carbon.  We  can,  therefore,  from  these 
data,  find  the  equivalent  of  any  fuel,  either  in  carbon  or 
hydrogen. 

'-•ic  When  a  fuel  contains  volatile  matters,  the  quantity  can 
be,  ascertained,  as  before  pointed  out,  by  ignition  in  a  close 
tube  or  crucible.  If,  further,  we  ascertain  the  proportion 
Qjf  lead  it  gives  with  litharge,  it  is  easy  to  calculate  the 
equivalent  in  carbon  of  the  volatile  matters,  and,  in  con- 
sequence, to  ascertain  its  calorific  value. 
.  •  ;j /.Supposing  that  a  substance  gives  by  distillation  C  parts 
of  coke,  or  carbon,  having  deducted  the  weight  of  the  ash 
and  of  volatile  substances,  and  that  it  produces  P  parts  of 
lead.^ith  litharge.  The  quantity  C  of  carbon  would  give 
34  x  C  of  lead  ;  the  quantity  of  volatile  matter  would  give 
but  P—  34  x  C  ;  it  would  be  equivalent  to  p— *—  of  carbon : 
whence  it  follows  that  the  quantity  of  heat  developed  by 
1jhe  charcoal,  the  volatile  matter,  and  the  unaltered  com- 


DR.  URE  ON  BERTHIER'S  METHOD.  149 

bustible,  will  be  to  each  other  as  the  numbers  34  x  C, 
P-34xC,  arid  P. 

Dr.  Ure  *  says,  speaking  of  the  above  method  of  assay, 
*  On  subjecting  this  theory  to  the  touchstone  of  experi- 
ment, I  have  found  it  to  be  entirely  fallacious.  Having 
mixed  very  intimately  10  grains  of  recently  calcined  char- 
coal with  1000  parts  of  litharge,  both  in  fine  powder,  I 
placed  the  mixture  in  a  crucible,  which  was  so  carefully 
covered  as  to  be  protected  from  all  fuliginous  fumes,  and 
exposed  it  to  distinct  ignition. 

'  No  less  than  603  grains  of  lead  were  obtained,  whereas, 
by  Berthier's  rule,  only  340  or  3 46 '6  were  possible.  On 
igniting  a  mixture  of  10  grains  of  pulverised  anthracite 
with  500  grains  of  pure  litharge  previously  fused  and 
pulverised,  I  obtained  380  grains  of  metallic  lead.  In  a 
second  experiment,  with  the  same  anthracite  and  the  same 
litharge,  I  obtained  450  grains  of  lead ;  and  in  a  third, 
only  350  grains.  It  is  therefore  obvious  that  this  method 
of  Berthier's  is  altogether  nugatory  for  ascertaining  the 
quantity  of  carbon  in  coals,  and  is  worse  than  useless 
in  judging  of  the  calorific  qualities  of  different  kinds  of 
fuel.' 

This  discrepancy  in  the  results  obtained  by  Dr.  Ure  is 
very  perplexing,  and  does  not  at  all  accord  with  Berthier's 
experience,  as  shown  by  his  experiments,  or  by  the  author's 
on  the  subject.  The  latter  never  had  a  difference  of  more 
than  50  grains,  and  in  general  only  two  or  three,  which 
latter  result  is  satisfactory.  The  only  precaution  he  found 
necessary  was  to  heat  very  gradually  until  the  mixture 
was  fully  fused,  and  then  to  increase  the  fire  to  bright 
redness  for  a  few  minutes. 

Further  experiments  have  been  made  by  the  author 
-on  this  subject,  and  he  has  succeeded  most  perfectly  in 
estimating  the  value  of  a  fuel.  With  the  litharge  of  com- 
merce, which  contains  much  minium,  the  process  is  never 
exact :  results  have  been  obtained  differing  as  much  as  40 
or  50  grains  when  the  litharge  employed  had  not  been 
purified,  and  to  purify  it  completely  is  a  troublesome 

*  '  Supplement  to  the  Dictionary  of  Arts,  Mines,  and  Manufactures.' 


150  URE'S   CALORIMETER, 

process.  This  difficulty  may  be  completely  obviated ,, 
however,  by  substituting  for  litharge,  white  lead,  using 
for  each  10  grains  of  fuel  700  grains  of  white  lead,  which 
are  well  mixed  with  it,  and  300  grains  of  pure  white  lead 
to  cover  the  mixture. 

When  the  whole  is  heated,  the  carbonate  of  lead  de- 
composes, forming  pure  lead  oxide,  which  is  then  reduced,, 
as  in  the  former  case.  By  this  process  the  results  corre- 
spond to  1  grain  in  the  quantity  of  lead  produced  from  a 
given  sample  of  fuel.  Of  course  great  care  must  be  taken 
that  the  white  lead  is  genuine. 

Commercial  samples  are  frequently  adulterated  with 
lead  sulphate  and  barium  sulphate,  lead  oxychloride,  zinc 
oxide,  &c.  This  is  a  serious  drawback  to  this  otherwise 
excellent  modification. 

The  following  is  the  method  of  ascertaining  the  calorific 
power  of  fuel,  employed  by  Dr.  Ure,  and  described  in  his 
'  Supplement.' 

'  The  following  calorimeter,  founded  upon  the  same 
principle  as  that  of  Count  Eumford,  but  with  certain  im- 
provements, may  be  considered  as  an  equally  correct  in- 
strument for  measuring  heat  with  any  of  the  preceding 
(Lavoisier's,  Meyers',  and  others),  but  one  of  much  more 
general  application,  since  it  can  determine  the  quantity 
of  heat  disengaged  in  combustion,  as  well  as  the  latent 
heat  of  steam  and  other  vapours. 

'  It  consists  of  a  large  copper  bath  capable  of  holding 
100  gallons  of  water.  It  is  traversed  four  times  backwards 
and  forwards  in  four  different  vessels,  by  a  zigzag  horizontal 
flue  or  flat  pipe,  nine  inches  broad  and  one  deep,  ending 
below  in  a  round  pipe,  which  passes  through  the  bottom 
of 'the  bath  and  receives  there  into  it  the  top  of  a  small 
black-lead  furnace,  the  innermost  crucible  of  which  con^ 
tains  the  fuel.  It  is  surrounded  at  the  distance  of  an  inch 
by  a  second  crucible,  which  is  inclosed  at  the  same  time  by 
the  sides  of  the  outermost  furnace,  the  stratum  of  stagnant 
air  between  the  crucibles  serving  to  prevent  the  heat  being 
dissipated  into  the  atmosphere  by  the  body  of  the  furnace. 
A  pipe  from  a  double  pair  of  bellows  enters  the  ashpit  of 


URE'S   CALORIMETER.  151 


the  furnace  at  one  side,  and  supplies  a  steady  but  gentle 
draught  to  carry  on  the  combustion  kindled  at  first  by 
half  an  ounce  of  burning  charcoal.  So  completely  is  the 
heat  which  is  disengaged  by  the  burning  fuel  absorbed  by 
the  water  in  the  bath,  that  the  air  discharged  at  the  top 
pipe  is  generally  of  the  same  temperature  as  the  atmo- 
sphere. The  vessel  is  made  of  copper,  weighing  2  Ibs.  per 
square  foot;  it  is  5^  feet  long,  1^  wide,  2  deep,  with  a 
bottom  54  feet  long,  and  1J  broad  upon  an  average.  In- 
cluding the  zigzag  tin-plate  flue,  and  a  rim  of  wrought 
iron,  it  weighs  altogether  85  Ibs.  Since  the  specific  heat 
of  copper  is  to  that  of  water  as  94  to  1,000,  the  specific 
heat  of  the  vessel  is  equal  to  that  of  8  Ibs.  of  water ;  for 
which,  therefore,  the  exact  correction  is  made  by  leaving 
8  Ibs.  of  water  out  of  the  600  or  1,000  Ibs.  used  in  the 
experiment. 

'  In  the  experiments  made  with  former  calorimeters  of 
this  kind,  the  combustion  wras  maintained  by  a  current  or 
draught  of  a  chimney  open  at  bottom,  which  carried  off 
at  the  top  orifice  of  the  flue  a  variable  quantity  of  heat, 
very  difficult  to  estimate. 

4  The  heating  power  of  the  fuel  is  measured  by  the 
number  of  degrees  of  temperature  wrhich  the  combustion 
of  1  Ib.  of  it  raises  600  or  1 ,000  Ibs.  of  water  in  the  bath,  the 
copper  substance  of  the  vessel  being  taken  into  account. 
1  Ib.  of  dry  wood  charcoal,  by  its  combustion,  causes 
0,000  Ibs.  of  water  to  become  20°  hotter.  For  the  sake  of 
brevity,  we  shall  call  this  calorific  energy  12,000  units. 
In  like  circumstance,  1  Ib.  of  Llangennock  coal  will  yield 
by  combustion  11,500  calorific  units.' 

This  vform  of  calorimeter  of  Dr.  Ure's  seems  to  possess 
many  advantages  over  Laplace's  and  others,  and  is,  no 
doubt,  very  convenient  in  use,  although  rather  bulky. 

The  instrument  known  as  Wright's  calorimeter  gives 
very  accurate  results,  and  is  the  one  most  generally  used 
now  in  experiments  on  the  heating  power  of  fuel,  in  all 
but  the  most  refined  investigations.  It  is  shown  in  the 
accompanying  figure  (fig.  67).  rj  Vo  •• 

The  copper  cylinder  A  B  is  filled  with  a  mixture  of  20 


152 


WRIGHT  S   CALOE1METER. 


grains  of  the  combustible,  and  240  of  the  deflagrating  com- 
pound, which  is  composed  of  three  parts  of  potassium 
chlorate,  and  one  of  potassium  nitrate.  A  little  piece  of 
cotton  soaked  in  potassium  chlorate  is  placed  partly  in  the 


FIG.  67. 


AB-3J  in. ;  diameter  f  in. 
CD=2in. 
CB,  socket  for  AB. 
Diameter  across  D=4  in. 
EF=6in. 

FG = 5  in. ;  diameter  H  G  =  1|  in. 
AB  weighs  39J  grammes. 
The  remainder  of  the  apparatus,  including 
the  stop-cock,  weighs  391  grammes. 


SCALE  OF  12  INCHK? 


mixture,  the  other  end  projecting  above  the  top  of  the 
cylinder ;  this  is  ignited,  quickly  covered  with  the  bell- 
shaped  part  of  the  apparatus,  and  immersed  in  a  measured 
quantity  of  water.  As  constructed,  the  whole  metallic 


PYROMETRIC   EXAMINATION   OF   FUEL.  153 

apparatus  weighs  6,642'7  grains,  and  with  this  weight 
290-1  grains  of  water  are  used.  The  temperature  is  re- 
corded before  and  after  making  the  experiment.  During 
the  deflagration  the  stop-cock  is  closed ;  it  is,  however, 
opened  before  taking  the  temperature  the  second  time.  A 
tenth  of  the  temperature  that  the  water  is  raised  by  the 
combustion  is  added  for  errors  that  are  incidental  to  the 
use  of  the  instrument. 

If  the  instrument  is  made  of  the  weight  above  given, 
the  result  is  obtained  by  a  very  simple  calculation.  Each 
Fahrenheit  degree  by  which  the  temperature  of  the  water 
has  been  augmented  corresponds  to  a  pound  of  water 
converted  into  steam. 

,     n  t    .  r   i  "* 

EXAMPLE. 

Fahr. 

Temp,  of  water  before  making  experiment  =  56° 
-  „  „      after  the  combustion         .  -  65 

9°  +  &th 
„       produced  by  the  combustion  =  9'1 

20  grains  of  the  coal  will  convert  into  steam  (maximum  effect)  9*1  Ibs.  of  water 

>ix  row  x  2240  =  Effectofaton 

5.  DETERMINATION  OF  THE  SPECIFIC  HEATING  POWER — This 
represents  the  heat  produced  from  a  certain  volume  of 
fuel.     It  may  be  ascertained  by  multiplying  the  absolute 
heating  power  by  the  specific  gravity. 

6.  DETERMINATION  OF  THE  PYROMETRIC  HEATING  POWER. — 
By   pyrometric   heating   power   is  meant  the  degree  of 
temperature  which  may  be  obtained  by  completely  burning 
the  fuel.     This  heating  power  not  only  depends  upon  the 
composition  of  the  fuel,  but  chiefly  on  the  time  required 
for  its  combustion,  and  this  again  depends  on  the  looseness 
and   inflammability  of  the   fuel.     The   absolute   heating 
power  of  hydrogen  is  greater  than  that  of  carbon,  but  with 
regard  to  the  pyrometric  heating  power  it  will  be  found 
that  the  reverse  is  the  case. 

Carbon  burned  in  contact  with  the  air  to  carbonic 
acid  will  produce  a  heat  of  2,558°  C. ;  if  burned  to  car- 
bonic oxide  it  only  produces  1,310° ;  hydrogen  burning  to 
water  will  produce  a  heat  of  2,080°.  From  this  we  learn 


154  ASSAY   OF   FUEL. 

that  fuel  rich  in  carbon,  such  as  anthracite,  coal,  and  coke, 
will  produce  a  greater  pyrometric  effect  than  fuel  rich  in 
hydrogen,  as  wood,  &c. 

Density  is  an  essential  quality  of  fuel  required  to  pro- 
duce great  pyrometric  effect.  This  is  proved  in  the  follow- 
ing way. 

When  atmospheric  air  first  acts  on  the  carbon  con- 
tained in  fuel,  carbonic  acid  is  formed,  and  the  tempera- 
ture rises  to  a  certain  degree,  but  on  passing  over  glowing 
coal,  carbonic  acid  becomes  converted  into  carbonic  oxide, 
and  this  causes  a  portion  of  the  heat  at  first  produced  to 
become  latent.  This  conversion  of  carbonic  acid  into  car- 
bonic oxide  is  more  easy  and  complete  as  the  fuel  used  is 
more  inflammable ;  and  as  a  greater  quantity  of  heat  is 
thereby  rendered  latent,  it  follows  that  the  heating  power 
of  such  a  fuel  is  inferior.  This  accords  with  general  ex- 
perience ;  for  it  is  well  known  that  coke  is  able  to  produce 
a  greater  heat  than  charcoal. 

Several  good  methods  for  determining  pyrometric 
heating  power  were  given  in  the  last  chapter. 

7.  DETERMINATION  OF  THE  VOLATILE  PRODUCTS  OF  CARBONI- 
SATION.— The  amount  of  volatile  matter  yielded  on  car- 
bonising a  fuel  depends  partly  on  the  composition  of  the 
fuel,  and  partly  on  the  temperature  employed.  If  a  fuel 
rich  in  oxygen  and  hydrogen  is  quickly  heated,  it  will  yield 
the  greatest  amount  of  volatile  products.  These  are 
partly  liquid  (tar,  naphtha,  and  acetic  or  ammoniacal  water), 
and  partly  gaseous  (carbonic  oxide,  carbonic  acid,  and 
light  and  heavy  carburetted  hydrogen).  "The  more  oxy- 
gen a  fuel  contains,  the  more  carbonic  acid  and  carbonic 
oxide  it  will  produce  ;  the  more  hydrogen  it  contains,  the 
more  illuminating  gas  it  yields.  The  applicability  of  a 
sample  of  coal  to  the  production  of  illuminating  gas 
depends  on  these  conditions. 

Coal  distilled  at  a  low  temperature  yields  much  tar  and 
comparatively  little  gas,  and,  when  a  very  high  temperature 
has  been  used,  less  tar  and  more  gas  is  produced,  but  the 
great  heat  will  have  reacted  on  the  gas  and  injured  its 
illuminating  qualities.  If  the  coal  contains  pyrites,  the 


EXAMINATION  OF  COKE  OF  FUEL.  155 

gas  will    contain    sulphur    compounds.     The   amount    of 
water  produced  is  generally  larger  than  that  of  the  tar. 

In  order  to  estimate  the  amount  of  volatile  matter  given 
off  from  any  particular  sample  of  coal,  proceed  in  the  fol- 
lowing manner :  Place  a  given  weight,  say  200  grains, 
of  the  coal  in  an  iron  tube,  closed  at  one  end,  to  the  other 
end  of  which  adapt,  by  means  of  a  cork,  a  glass  or  other 
tube,  which  must  be  conducted  into  an  inverted  jar  full  of 
water  standing  in  the  pneumatic  trough.  Raise  the  tem- 
perature very  gradually  to  redness,  and  continue  the  heat 
until  no  more  gas  is  given  off,  then  ascertain  its  quantity 
in  cubic  inches,  with  due  correction  for  temperature  and 
pressure. 

8.  EXAMINATION  OP  THE  COKE  OR  CHARCOAL  LEFT  BEHIND  ON 
CARBONISATION. — The  amount  of  coke  or  charcoal  yielded 
by  a  sample  of  fuel  is  found  by  the  last  operation.     This 
residue  is  the  amount  of  coke  which  that  particular  sample 
of  coal  produces  ;  and  its  weight,  divided  by  two,  gives 
the  percentage  of  coke. 

The  process  of  coking,  charring,  or  carbonising  fuel, 
whilst  it  drives  off  some  of  the  valuable  hydrocarbon  con- 
stituents, also  gets  rid  of  all  the  aqueous  elements.  And 
therefore,  the  coke  or  charcoal  which  is  left  behind  has 
its  value  greatly  increased  when  high  temperatures  are 
required,  although,  from  the  absence  of  flame-yielding 
constituents,  it  is  much  more  difficult  to  ignite. 

The  degree  of  inflammability  of  coke  or  charcoal  is 
relatively  the  same  as  that  of  the  raw  fuel  from  which  they 
were  produced.  The  more  inflammable  a  fuel  has  been, 
the  more  inflammable  will  be  the  coke  or  charcoal  pro- 
duced from  it. 

The  temperature  employed  in  the  carbonisation,  as  has 
been  already  explained,  exerts  great  influence  on  the  yield 
of  coke. 

If  the  fuel  contains  iron  pyrites,  part  of  the  sulphur 
goes  off  in  the  volatile  portion,  but  from  |  to.^  is  retained 
in  the  form  of  FeS. 

9.  DETERMINATION  OF  THE  AMOUNT  OF  ASH. — In  order  to 
ascertain  the  amount' of  ash  :  Fully  ignite  about  50  grains 


156  DETERMINATION    OF   SULPHUR   IN   FUEL. 

of  coal  in  a  platinum  capsule,  allowing  the  air  to  have  free 
access  all  the  time  until  nothing  but  ash  is  left.  Its 
amount  may  then  be  ascertained  by  weighing  :  good  fuel 
should  contain  little  ash.  It  may  vary  from  1  to  10  per 
cent.,  but  if  it  exceeds  5  per  cent,  it  becomes  deleterious. 
The  chemical  composition  of  the  ash  also  influences  the 
quality  of  the  fuel  to  some  extent. 

10.  DETERMINATION  OF  THE  AMOUNT  OF  SULPHUR. — This  is 
an  important  operation  in  the  assay,  as  a  coal  containing 
sulphur  cannot  be  employed  for  particular  operations,  and, 
indeed,  those  which  contain  much  sulphur  ought  only  to 
be  used  for  the  commonest  purposes.  This  assay  is  most 
important  to  ironmasters  as  well  as  to  steamboat  and  other 
companies,  who  consume  fuel  under  steam-boilers  ;  and 
the  coal  they  purchase  should  always  be  subjected  to  this 
particular  test,  as  sulphur  has  a  corroding  and  destroying 
action  on  iron  and  copper.  Where  sulphurous  coals  are 
continually  burnt  under  boilers,  the  metal  of  the  latter 
becomes  deteriorated,  and  the  boiler  is  rapidly  rendered 
useless.  Sulphur  exists  in  coal  in  the  form  of  iron  pyrites  ; 
this  can  generally  be  detected  by  its  brassy  colour.  Some 
coals  and  lignites  also  contain  calcium  sulphate,  and  in 
rare  cases  barium  sulphate. 

The  process  for  the  determination  of  the  amount  of 
sulphur  in  coal  is  not  difficult.  1  part  of  the  coal  is  to  be 
finely  pulverised,  and  then  mixed  with  7  or  8  parts  of 
potassium  nitrate,  16  parts  of  common  salt,  and  four  parts 
of  potassium  carbonate,  all  of  which  must  be  perfectly 
pure  ;  the  mixture  is  then  placed  in  a  platinum  crucible 
and  gently  heated.  At  a  certain  temperature,  the  whole 
ignites  and  burns  quietly.  The  heat  is  then  increased  until 
the  mass  is  fused  :  the  operation  is  finished  when  the  mass 
is  white.  It  must,  when  cold,  be  dissolved  in  water,  the 
solution  slightly  acidulated  by  means  of  hydrochloric  acid, 
and  barium  chloride  added  to  it  as  long  as  a  white  preci- 
pitate forms.  This  precipitate  is  barium  sulphate,  which 
must  be  collected  on  a  filter,  washed,  dried,  ignited,  the 
filter  burnt  away,  and  the  remaining  barium  sulphate 
weighed  :  every  116  parts  of  it  indicate  16  of  sulphur.  ;-i 


DETERMINATION   OF   SULPHUR    IX    FUEL.  157 

Dr.  Price  lias  drawn  attention  to  a  source  of  error 
which  has  hitherto  escaped  notice  in  the  estimation  of  sul- 
phur, where  fusion  of  the  substance  with  nitre  is  the  pro- 
cess employed.  This  author  has  found  that  unless  great 
care  be  taken  to  prevent  the  fused  mass  passing  over  to 
the  outside  of  the  vessel,  and  so  coming  in  contact  with 
the  flame,  or  products  of  combustion,  an  appreciable  and, 
in  some  cases,  serious  error  will  arise,  owing  to  the  sul- 
phuric acid  produced  from  the  sulphurous  acid  in  the 
flame — a  product  of  the  oxidation  of  the  sulphide  of  car- 
bon contained  in  the  gas — combining  with  the  potash  of 
the  fused  salt.  Several  experiments  have  been  made  to 
ascertain  the  amount  of  error  that  may  be  occasioned  from 
the  above  cause.  In  one  instance,  the  flame  issuing  from 
a  Bunsen's  burner  was  made  to  strike  against  a  little  fused 
nitre  on  the  under-side  of  a  small  platinum  dish,  when,  in 
three  quarters  of  an  hour,  as  much  sulphuric  acid  w^as 
obtained  as  is  equivalent  to  12  milligrammes  of  sulphur. 
As  a  check  on  these  experiments,  nitre  was  fused  by  the 
flame  of  the  spirit  lamp,  when,  as  was  to  be  anticipated, 
not;  a  trace  of  sulphuric  acid  could  be  detected  upon  the 
addition  of  a  barium-salt  to  the  aqueous  solution  of  this 
fused  mass,  rendered  acid  by  hydrochloric  acid.  In  de- 
terminations of  sulphur  in  coke  or  coal,  great  care  should, 
therefore,  be  taken  to  prevent  any  of  the  fused  saline  con- 
tents of  the  crucible  from  getting  on  to  the  outside.  In 
fusing  pig-iron  with  nitre,  a  process  recommended  by  some 
for  the  estimation  of  the  sulphur  it  contains,  the  mass, 
especially  if  the  iron  be  rich  in  manganese,  invariably 
creeps  over  to  the  outer  wall  of  the  crucible ;  and  it  is, 
therefore,  impossible  to  obtain  correct  results  when  the 
operation  is  conducted  over  the  gas  flame.  The  assayist 
should  for  these  reasons  always  employ  a  spirit  flame  in 
preference  to  gas  in  sulphur  determinations. 

Teikichi  Makamura  recommends  the  following  proce- 
dure :  3  or  4  parts  of  the  mixed  alkaline  carbonates,  or  of 
sodium  carbonate,  are  intimately  mixed  with  one  part  of 
coal  in  very  fine  powder  in  a  large  platinum  dish.  The 
mixture  is  heated  at  first  very  gently,  a  spirit  lamp  being 


158  ASSAY   OF   FUEL. 

used  instead  of  a  Bunsen,  to  prevent  possible  absorption 
of  sulphur  ;  the  heat  is  then  raised  slowly  without  attain- 
ing that  of  visible  redness,  until  the  surface  becomes 
only  faintly  grey.  No  smoke  or  odorous  gases  should 
escape  during  the  whole  of  the  oxidation.  The  tem- 
perature is  now  raised  to  a  faintly  red  heat  for  sixty 
minutes,  at  the  end  of  which  time  the  mass  is  perfectly 
white  or  reddish  if  iron  be  present.  The  mass  is  not 
to  be  stirred  during  the  ignition.  The  residue  is  heated 
with  water,  filtered,  and  the  sulphates  determined  in 
the  ordinary  way. 

11.  EXAMINATION  OF  OTHER  PECULIARITIES  OF  FUEL. — 
Besides  the  above-named  examinations,  the  assayist  should 
notice  the  degree  of  inflammability  of  the  fuel,  and  whether 
any  particular  smell  is  evolved  during  combustion  ;  whether 
the  coal  is  good  for  coking  purposes ;  whether  it  burns 
with  a  large  smoky  flame  or  a  luminous  flame  ;  whether  it 
burns  quietly  or  with  decrepitation  ;  and  whether  the  ash 
is  dusty  or  fusible,  and  likely  to  accumulate  and  clog  up 
the  grate-bars. 

CALCULATION  OF  RESULTS. — It  may  be  sufficient  here  to 
state  that,  beside  the  percentage  composition  of  the  coal, 
it  is  proper  to  reduce  the  composition  to  the  combustible 
=  100,  in  order  to  obtain  a  proper  comparative  estimate 
of  the  character  of  the  fuel  itself  (in  regard  to  the  propor- 
tion of  bitumen  and  carbon),  and  of  the  amount  and 
quality  of  the  impurities  (ash  and  moisture).  It  has  also 
been  shown  that,  for  considerable  areas  of  the  coal-field, 
the  sum  of  the  constituents  on  the  scale  of  combustible  = 
100  is  the  proper  calorific  equivalent,  and  that  the  percent- 
age of  the  combustible  in  the  fuel  gives  a  proper  estimate 
of  its  value. 

ASSAY  OF  COAL  BEFORE  THE  BLOWPIPE. — The  blowpipe 
method  is  well  adapted  to  the  assaying  of  coal.  Not  only 
does  the  portableness  of  the  apparatus  make  it  very  con- 
venient for  use  away  from  home,  wherever  the  balance 
can  be  set  up ;  but  its  use  at  home  is  quite  as  satisfactory 
on  the  score  of  exactness  as  the  assay  with  the  muffle  or 
retort,  or  large  platinum  crucible  and  large  balance.  Mr. 


ASSAY   OF   FUEL,  159 

J}.  S.  Lyman  gives  the  following  directions  for  carrying 
out  this  assay  : — 

Besides  the  ordinary  pieces  of  the  blowpipe  apparatus, 
as  made  at  Freiburg,  all  that  needs  to  be  made  expressly 
for  the  coal  assay  is  a  small  covered  platinum  crucible  of 
the  same  size  and  shape  as  the  clay  crucibles  of  that  appa- 
ratus ;  and  there  must  be  a  little  ring  for  the  crucible  to 
stand  on,  of  German  silver,  about  three-eighths  of  an  inch 
across  and  half  that  in  height.  Such  a  crucible  cover  and 
ring  weigh  about  2|  grammes  more  than  the  ordinary 
metallic  cup  that  rests  on  the  pan  of  the  balance ;  the 
•crucible  and  ring  with  the  cover  weigh  less  than  2  grammes 
more  than  the  cup.  If  it  be  desired  to  determine  the 
amount  of  hygroscopic  moisture  in  the  coal,  a  small  drying 
bath  must  be  made  too ;  but  the  hygroscopic  water  in 
ordinarily  well-dried  coals  (not  brown  coals)  is  of  little 
importance. 

The  size  of  the  crucible  allows  the  coking  of  200  to 
600  or  more  milligrammes  of  coal,  according  to  the  dry- 
ness  of  the  coal  and  the  extent  of  its  swelling  up  when 
heated  ;  and  as  the  blowpipe  balance  weighs  within  l-10th 
of  a  milligramme,  it  is  easy  to  weigh  within  much  less  than 
1-1  Oth  of  one  per  cent,  of  the  amount  of  coal  assayed, 
much  nearer,  in  fact,  than  the  exactness  of  the  coke  assay 
in  other  respects.  On  this  point,  indeed,  the  blowpipe 
assay  is  quite  as  good  as  the  assay  with  the  larger  balance, 
especially  the  muffle  assay,  where  the  coal  must  be  brushed 
into  a  clay  receptacle  after  weighing,  and  the  coke  or  ashes 
brushed  off  from  it  before  weighing ;  while  here  the  cru- 
cible is  weighed  each  time  without  removal  of  its  contents, 
and  without  danger,  therefore,  of  losing  anything  or  adding 
any  dust.  It  may  be  objected  that  the  smallness  of  the 
amount  of  coal  that  can  be  assayed  with  the  blowpipe 
makes  it  a  less  trustworthy  indicator  of  the  general  com- 
position of  the  coal  than  a  larger  assay  ;  but  the  size  of 
the  lumps  or  powder  assayed  may  be  made  finer  accord- 
ingly, so  that,  when  mixed  up,  an  equally  just  sample  of 
the  whole  mass  would  be  got  for  the  small  assay  as  for  the 
large. 


160  ASSAY   OF    FUEL. 

Anyone  who  has  had  a  little  experience,  both  in  the  use- 
of  the  blowpipe  and  in  the  ordinary  muffle  assay  of  coalr 
will  scarcely  need  any  further  teaching  for  the  coal  assay 
with  the  blowpipe.  For  others  it  is  worth  while  to  say 
that  the  coal  may  be  assayed  either  in  a  fine  powder  or  in 
little  lumps,  and  either  with  a  slowly  increasing  or  with  a 
quickly  increasing  heat.  A  quick  heat  will  give  less  coke 
by  several  per  cents.,  but  will  often  make  a  dry  coal  cake 
together  that  would  not  cake  with  a  slow  heat.  The 
cover  of  the  crucible  should  be  left  open  a  little,  for  the 
easy  escape  of  the  gas,  but  covered  enough  to  prevent  any 
flying  off  of  solid  material.  The  heat  should  increase  to- 
redness,  and  as  soon  as  the  escaping  gas  stops  burning  the 
heat  should  be  stopped.  As  some  coals  part  with  their 
gas  more  quickly  than  others,  of  course  no  definite  time 
can  be  fixed  for  heating  all  coals  ;  but  the  burning  of  the 
gas  is  a  good  enough  sign.  Care  should  be  taken  not  to 
let  the  coke  take  up  moisture  from  the  air  before  weighing, 
as  it  will  quickly  do  if  it  has  a  chance.  Of  course,  owing 
to  the  different  effects  of  quick  or  slow  heating,  a  certain 
uniformity  of  result,  even  with  perfectly  uniform  samples 
of  coal,  can  only  be  got  without  error  by  practice  and  by 
mechanical  skill,  by  reproducing  with  nicety  the  same  con- 
ditions in  successive  assays. 

After  the  coke  has  been  weighed,  it  can  be  heated 
again  with  very  free  access  of  air,  say  with  the  crucible 
tilted  to  one  side,  and  the  cover  off,  until  everything  is 
thoroughly  burnt  to  ashes  ;  and  these  should  be  re-heated 
until  no  change  for  the  less  is  made  in  the  weight.  With 
free  burning,  soft  (semibituminous)  coals  this  burning  to 
ashes  is  v,ery  slow,  so  that  it  is  very  fatiguing  or  even  im- 
possible to  carry  it  out  with  a  blowpipe  ;  but  in  that  case 
the  crucible  may  be  heated  over  a  Bunsen  gas-burner  or 
an  alcohol  lamp,  and  left  to  glow  for  hour  after  hour. 
The  coking  is  far  more  conveniently  done  in  the  same  way 
than  by  blowing  with  the  mouth. 

As  an  illustration  of  the  degree  of  accuracy  which  this 
method  may  be  expected  to  give,  the  author  adduces  a 
pair  of  blowpipe  assays,  made  five  years  ago,  of  some  West 


ASSAY   OF   FUEL.  161 

Virginia  asphaltum,  that  seemed  itself  to  be  much  more 
uniform  in  composition  than  coal  from  different  benches  in 
one  bed  is  apt  to  be  : — 

Volatile  Matter  Coke  Ashes 

No.  1         .         .     47-29  per  cent.         52-71  per  cent.         1-65  per  cent. 
No.  2        .        .     46-93      „  53-07     „  1-61      „ 

Mean        .         .     47-11      „  52-89      „  173      „ 

VALUATION  OF  COAL  FOE  THE  PRODUCTION  OF  ILLUMINATING 
GAS. — Take  100  grs.  of  the  coal  in  small  lumps,  so  that 
they  may  be  readily  introduced  into  a  rather  wide  com- 
bustion-tube. This  is  drawn  out  at  its  open  end  (after  the 
coal  has  been  put  in)  so  as  to  form  a  narrow  tube,  which 
is  to  be  bent  at  right  angles  ;  this  narrower  open  end  is  to 
be  placed  in  a  wider  glass  tube,  fitted  tight  into  a  cork 
fastened  into  the  neck  of  a  somewhat  wide-mouthed  bottle 
serving  as  tar  vessel  (hydraulic  main  of  the  gasworks). 
The  cork  alluded  to  is  perforated  with  another  opening, 
wherein  is  fixed  a  glass  tube,  bent  at  right  angles  for  con- 
veying the  gas  first  through  a  chloride  of  calcium  tube, 
next  through  Liebig's  potash  bulbs  containing  a  solution 
of  caustic  potash,  having  lead  oxide  dissolved  in  it.  Next 
follows  another  tube,  partly  filled  with  dry  caustic  potash, 
and  partly  with  calcium  chloride ;  from  this  last  tube  a 
gas-delivery  tube  leads  to  a  graduated  glass  jar  standing 
over  a  pneumatic  trough,  and  acting  as  gas-holder.  Before 
the  ignition  of  the  tube  containing  the  coal  is  proceeded 
with,  all  the  portions  of  the  apparatus  are  carefully  weighed 
and  next  joined  by  means  of  india-rubber  tubing.  After 
the  combustion  is  finished,  which  should  be  carefully  con- 
ducted, so  as  to  prevent  the  bursting  or  blowing  out  of 
the  tube,  the  different  pieces  of  the  apparatus  are  discon- 
nected and  weighed  again.  The  combustion- tube  has  to 
be  weighed  with  the  coal  after  it  has  been  drawn  out  at 
its  open  end,  and  with  the  coke  after  the  end  of  the  com- 
bustion when  it  is  again  cold  ;  and  for  that  reason  care  is 
required  in  managing  it.  We  thus  get  the  quantity  of 
tar,  ammoniacal  water,  carbonic  acid,  and  sulphuretted 
hydrogen  (as  lead  sulphide) ;  and  the  gas  is  measured  by 

H 


162  ASSAY  OF   FUEL. 

immersing  the  jar  in  water,  causing  it  to  be  at  the  same 
level  inside  and  out.  Empty  the  Liebig's  bulbs  into  a 
beaker,  and  separate  the  lead  sulphide  by  filtration,  wash 
carefully,  dry  at  100°  C.,  and  weigh.  From  the  lead  sul- 
phide the  sulphuretted  hydrogen  present  is  calculated. 
This  process,  devised  by  the  late  Dr.  T.  Eichardson,  of 
Newcastle-on-Tyne,  was  found  by  him  to  yield  very  trust- 
worthy results,  so  as  to  be  suitable  for  stating  what 
quantity  of  gas  a  ton  of  coal  thus  analysed  would  yield. 


163 


CHAPTEK  VI. 

REDUCING   AND    OXIDISING   AGENTS FLUXES,    ETC. 

IN  some  assay  operations  in  the  dry  way,  bodies  are  heated 
in  suitable  vessels  per  se ;  but  it  is  more  often  necessary  to 
add  to  the  bodies  submitted  to  assay  other  substances, 
which  are  varied  according  to  the  nature  of  the  change  to 
be  effected.  These  substances  may  be  divided  into  five 
classes :  I.  reducing  agents ;  II.  oxidising  agents ;  HI. 
desulphurising  agents  ;  IV.  sulphurising  agents  ;  and  lastly, 
V.  fluxes  properly  so  called. 

I.    REDUCING    AGENTS. 

The  substances  belonging  to  this  class  have  the  power 
of  removing  oxygen  from  those  bodies  with  which  it  may 
be  combined.  In  assaying,  the  substance  under  examina- 
tion is  generally  fully  oxidised  either  naturally  or  artifi- 
cially before  reduction  is  required  to  be  effected.  The 
most  common  reducing  agents  are  as  follows  : — 

1.  Hydrogen  gas. 

2.  Carbon. 

3.  The  fatty  oils,  tallow,  pitch,  and  resins. 

4.  Sugar,  starch,  and  gum. 

5.  Tartaric  acid. 

6.  Oxalic  acid. 

7.  Metallic  iron  and  lead. 

HYDKOGEN  GAS. — The  most  common  method  of  prepar- 
ing this  gas  consists  in  dissolving  zinc  in  dilute  sulphuric 
acid.  But  as  this  plan  gives  the  gas  in  the  moist  state,  it 
must  be  dried  by  being  allowed  to  bubble  through  oil  of 

M  2 


164  EEDUCING   AGENTS. 

vitriol  or  by  being  passed  through  a  bottle  containing 
fragments  of  dried  calcium  chloride  before  it  is  used  for 
assaying  purposes.  This  gas  will  only  be  required  in  very 
accurate  assays,  which  are  generally  performed  where 
there  are  ample  conveniences  for  generating  pure  hydro- 
gen gas.  The  gas  is  inodorous,  invisible,  and  colourless 
when  absolutely  pure.  It  is  a  most  powerful  reducing 
agent,  and  reduces  a  great  number  of  metallic  oxides  at  a 
red  or  white  heat,  viz.  the  oxides  of  lead,  bismuth,  copper, 
antimony,  iron,  cobalt,  nickel,  tungsten,  molybdenum,  and 
uranium.  When  any  metal  is  required  in  a  state,  of  abso- 
lute purity,  this  is  the  only  reducing  agent  admissible,  as 
others  give  the  metal  combined  with  a  certain  proportion 
of  carbon. 

CARBON — Found  in  large  quantities  in  the  mineral 
kingdom,  but  generally  combined  with  other  bodies.  In 
a  state  of  purity  it  constitutes  the  diamond.  The  diamond, 
like  all  other  species  of  carbon,  is  unacted  on  by  the  highest 
possible  temperature  when  in  close  vessels.  It  burns  in 
atmospheric  air  and  oxygen  gas,  but  requires  for  combus- 
tion a  higher  temperature  than  ordinary  charcoal.  After 
the  diamond,  the  varieties  of  carbon  found  in  nature  or 
artificially  prepared,  are  : — 

1.  BLACK-LEAD  or  GRAPHITE. — This  is  a  mineral  found 
in  beds  in  the  primitive  formations,  principally  in  granite 
and  mica-schist.  It  is  generally  mixed  with  earthy  sub- 
stances, and  rarely  yields  less  than  10  per  cent,  of  ash. 
Before  employing  it  for  reduction  purposes  it  should  be 
purified.  Lowe  *  has  given  an  excellent  plan  for  effecting 
this  object. 

DETERMINATION  OP  THE  VALUE  OF  GRAPHITE. — G.  C.  Witt- 
stein  f  heats  a  gramme  ©f  the  sample  to  dull  redness,  and 
takes  the  loss  as  water.  The  residue  is  ground  up  with 
3  grammes  of  a  mixture  of  equal  equivalents  of  potassium 
and  sodium  carbonates,  introduced  into  a  platinum' cru- 
cible, covered  with  one  gramme  of  potash  or  soda,  and 
slowly  heated  to  redness.  The  crust  which  is  formed 

*  Polyt.  Centr.  1855,  p.  1404.  f  Dingler's  Polyt.  Journal,  216,  45. 


REDUCING   AGENTS.  165 

must  be  from  time  to  time  pushed  down  with  a  platinum 
wire.  After  fusion  for  half  an  hour  it  is  let  cool,  softened 
with  water,  heated  almost  to  a  boil  for  a  quarter  of  an 
hour,  filtered,  washed  well,  and  the  liquid  set  aside. 

The  residue  on  the  filter  is  dried,  placed  in  a  small 
flask,  the  ashes  of  the  filter  added,  and  about  three  grms. 
of  hydrochloric  acid  (sp.  gr.  1-12)  poured  in.  On  the 
mixture  becoming  slightly  gelatinous  a  few  more  drops  of 
the  acid  are  added,  the  digestion  is  continued  for  an  hour, 
the  mixture  diluted  with  water,  filtered,  and  washed.  Pure 
graphitic  carbon  remains  on  the  filter,  and  is  dried,  slightly 
ignited,  and  weighed.  The  acid  filtrate  mixed  with  the 
former  one  of  an  alkaline  character  is  evaporated  to  dry- 
ness,  and  in  it  silica,  alumina,  ferric  oxide,  &c.,  are  deter- 
mined in  the  usual  manner. 

2.  ANTHRACITE. — This  is  another  species  of  fossil  carbon 
much  resembling  ordinary  coal,  but  differing  from  it  by 
burning  with  neither  smell,  smoke,  nor  flame. 

3.  COKE. — This   is  the  residue   of  coal   after   all   the 
volatile  matter  is   expelled.     It   is   generally  iron-black, 
and  has  nearly  a  metallic  lustre ;  it  is  difficult  to  inflame, 
and  burns  well  only  in  small  pieces,  but  gives  a  very  in- 
tense heat.     Oven  or  furnace  coke  is  preferable,  as  it  is 
harder,  lasts  longer,  and  is  more  economical  in  use. 

4.  WOOD  CHARCOAL. — This  is  obtained  by  burning  the 
woody  part  of  plants,  with  a  limited  supply  of  air,  so  as 
to  drive  off  all  their  volatile  matters,  and  leave  merely 
their  carbon.     It  is  this  kind  that  is  generally  employed 
in  assays.    It  ought  to  be  chosen  with  care,  well  pulverised, 
passed  through  a  sieve,  and   preserved   in  well-stopped 
vessels.     Wood  charcoal  is  never  perfectly  pure,  generally 
containing,  besides  ash,   a  proportion   of  hydrogen   and 
watery  vapour  ;  these  bodies  are  not  generally  prejudicial, 
but  in  some  experiments  ash  must  not  be  present :  in  that 
case  pure  charcoal  may  be  procured  by  heating  sugar  to 
redness  in  a  closed  crucible. 

The  advantage  of  carbon  as  a  reducing  agent  consists 
in  its  great  affinity  for  oxygen,  which  at  a  red  heat  sur- 
passes that  of  most  other  substances.  Charcoal  by  itself 


166  REDUCING   AGENTS. 

possesses  two  inconveniences  :  first,  it  has  the  property  of 
combining  with  many  metals ;  and  in  the  second  place,  it 
is  infusible,  and  cannot  combine  with  vitreous  substances. 
The  property  it  possesses  of  combining  with  iron,  nickel, 
cobalt,  &c.,  is  of  no  consequence  to  the  assay er,  for  the 
increase  of  weight  it  gives  is  not  material,  excepting  under 
the  circumstances  to  be  hereafter  pointed  out ;  but  its 
in  fusibility  and  inability  to  combine  with  fluxes  is  a  very 
serious  inconvenience  ;  for  after  the  reduction,  that  portion 
which  has  not  been  consumed  remains  disseminated  with 
the  grains  of  metal  in  the  fused  slag,  and  prevents  the 
separation  of  all  the  metal,  and  the  consequent  formation 
of  a  good  button  ;  a  large  quantity  of  charcoal  can  thus 
irreparably  injure  an  assay.  This  inconvenience  does  not 
happen,  however,  when  an  oxide  is  reduced  by  cementa- 
tion in  a  lined  crucible,  but  there  are  some  cases  in  which 
this  mode  of  reduction  is  inadmissible. 

Coke  should  never  be  used  as  a  reducing  agent  in 
assays  when  it  is  possible  to  avoid  it.  It  often  contains 
a  very  large  proportion  of  earthy  and  other  extraneous 
matters  (more  particularly  sulphur,  which  is  very  in- 
jurious). Coke  is  never  so  good  as  wood  charcoal  as  a 
reducing  agent,  because  it  burns  more  slowly.  When  it 
is  used,  the  temperature  employed  for  an  assay  must  be 
much  increased. 

Coal  is  nearly  always  inconvenient,  because  it  swells 
by  heat ;  nevertheless,  as  it  is  not  required  in  very  large 
quantities,  it  is  sometimes  employed,  being  finely  powdered 
and  sifted  previous  to  use. 

THE  FATTY  OILS. — The  name  oil  is  generally  given  to 
those  bodies  that  are  fat  and  unctuous  to  the  touch,  more 
or  less  fluid,  insoluble  in  water,  and  combustible.  They 
all  become  solid  at  various  degrees  of  temperature. 
There  are  some  which,  at  the  temperature  of  our  climate, 
have  constantly  a  solid  form,  as  butter,  palm-oil,  cocoa-nut- 
oil,  &c. 

TALLOW  is  an  animal  product  analogous  to  the  fatty  oils 
in  properties. 

RESINS. — The  greater  part  of  the  resins  are  solid,  but 


EEDUCIXG   AGEXTS.  167 

some  are  soft.  They  are  brittle,  with  a  vitreous  and 
shining  fracture,  and  are  often  transparent.  They  are  very 
fusible,  but  cannot  be  raised  to  their  boiling  point  without 
partial  decomposition. 

Although  all  the  bodies  just  mentioned  consume  in 
their  combustion  a  large  quantity  of  oxygen,  they  cannot 
generally  effect  the  total  reduction  of  an  oxide  on  account 
.of  their  volatility  ;  so  that,  before  the  temperature  at 
which  the  reduction  takes  place  can  be  attained,  the 
greater  part  of  the  reducing  agent  has  been  expelled. 
They  generally  act  only  by  virtue  of  the  small  carbonaceous 
residue  produced  by  the  action  of  heat ;  so  that  their  use 
is  very  limited  and  uncertain.  Whenever  they  are  em- 
ployed as  reducing  agents,  without  covering  the  substance, 
a  loss  is  experienced,  on  account  of  the  bubbling  and  boil- 
ing caused  by  their  decomposition :  this  will  always  take 
place  unless  the  contents  of  the  crucible  be  covered  with 
charcoal  powder.  Oils  are  very  serviceable  in  the  reduc- 
tion of  a  large  mass  of  oxide  by  cementation  ;  in  this  case, 
after  the  oxide  has  been  placed  in  the  crucible,  as  much 
oil  is  added  as  the  oxide  and  the  lining  of  the  crucible  will 
soak  up.  Fat  or  resin  is  also  used  to  prevent  the  oxida- 
tion of  the  surface  of  a  metallic  bath  (as  in  the  fusion  of 
bar-lead  samples),  by  coating  the  metal,  and  preventing 
the  action  of  the  atmospheric  oxygen. 

SUGAR  in  its  decomposition  by  heat  leaves  a  much  larger 
proportion  of  carbon  than  the  oils,  fats,  or  resins  ;  so  that 
it  would  appear  serviceable  as  a  reducing  agent.  There 
are  some  cases  in  which  it  may  be  used  with  advantage, 
but  it  undergoes  a  great  increase  in  volume  when  heated  ; 
so  that  losses  in  an  assay  may  occur  by  the  use  of  this 
agent.  To  purify  sugar  from  mineral  ingredients  it  should 
be  recrystallised  from  alcohol.  It  then  may  be  used 
as  such,  or  after  carbonisation.  It  yields  about  14  per 
cent,  of  charcoal :  this  is  pure  carbon,  and  leaves  no  resi- 
due when  burnt ;  it  is,  therefore,  preferable  to  wood  char- 
coal in  cases  where  no  foreign  matter  should  be  introduced 
into  the  assay. 

STARCH,  well  dried,  and,  better  still,  torrified,  is  em- 


168  COMPARATIVE   REDUCING   POWER. 

ployed  with  advantage  as  a  reducing  agent,  and  is  better 
than  sugar,  as  it  neither  fuses,  swells  up,  nor  spirts,  and  in 
many  cases  is  even  preferable  to  charcoal,  because  it  is  in 
such  a  fine  state  of  division  that  it  can  be  more  readily  and 
intimately  mixed  with  the  substance  to  be  reduced.  Wheat 
and  rye  flour  have  nearly  the  same  qualities  as  starch. 
They  are  sometimes  used. 

GUM  decrepitates  slightly  by  heat,  softens,  agglomerates, 
and  boils,  without  spirting.  The  gums  can  be  employed  as 
reducing  agents  under  the  same  circumstances  as  sugar  and 
starch,  but  the  two  latter  are  preferable,  because  they  con- 
tain no  earthy  substances. 

TARTARIC  ACID  is  the  reducing  agent  in  cream  of  tartar > 
or  argol,  of  which  so  frequent  use  is  made  ;  but  the  acid  is 
never  employed  by  itself.  When  heated  in  close  vessels,, 
it  fuses  and  decomposes,  giving  off  combustible  gases,  leav- 
ing a  little  charcoal.  It  burns  when  heated  in  contact 
with  air,  giving  rise,  to  a  peculiar  and  not  unpleasant 
odour. 

OXALIC  ACID  fuses  at  a  temperature  of  208°  without 
decomposing,  but  when  heated  to  230°  it  is  decomposed,, 
giving  rise  to  carbonic  acid,  carbonic  oxide,  and  a  little 
formic  acid  vapour,  and  when  heated  strongly  some  por- 
tions volatilise  without  decomposition ;  it  does  not  leave  a 
carbonaceous  residue. 

The  property  which  oxalic  acid  possesses  of  not  leaving 
a  residue  would  render  it  remarkably  valuable  for  the  re- 
duction of  the  metallic  oxides  in  cases  where  the  slightest 
trace  of  carbon  is  to  be  avoided,  if  its  reducing  power  were 
greater ;  but  it  decomposes  at  a  low  temperature,  and  in 
burning  absorbs  but  a  small  quantity  of  oxygen,  especially 
when  it  has  not  been  dried ;  so  that  even  for  the  most 
easily  reducible  oxides  a  .large  proportion  must  be  em- 
ployed. When  it  is  combined  with  a  base,  as  potash  in 
potassium  binoxalate,  its  reducing  power  is  much  aug- 
mented. 

AMMONIUM  OXALATE,  when  heated  in  close  vessels,  is  de- 
composed. Its  reducing  power  is  nearly  double  that  of 
oxalic  acid. 


COMPARATIVE   REDUCING   POWER. 


169 


COMPARATIVE  REDUCING  POWER  OF  THE  ABOVE  AGENTS. — In 
order  to  give  an  idea  of  the  comparative  reducing  power 
of  the  agents  just  described,  the  result  of  some  assays 
made  on  them  by  Berthier,  by  means  of  litharge,  are  given 
below. 

By  heating  the  same  weight  of  each  reducing  agent 
with  an  excess  of  litharge,  buttons  of  lead  were  obtained, 
whose  weights  were  proportional  to  the  quantity  of  oxygen 
absorbed,  and  by  comparing  them  with  each  other  the  re- 
ducing power  of  each  flux  is  given  ;  by  taking  for  unity 
the  weight  of  the  reagent,  calculation  has  proved  that 
1  part  of  pure  carbon  reduces  from  litharge  34*31  of 
lead.  The  following  are  the  results  of  Berthier 's  experi- 
ments :— 

Hydrogen  . 

Pure  carbon 

Calcined  woe 

Amber  resin 

Ordinary  wo< 

Animal  oil 

Tallow 

Eesin 

Sugar 

Terrified  starch  . 

Common  starch  . 

Gum-arabic 

Tartaric  acid 

Ammonium  oxalate 

Oxalic  acid 

It  must  be  borne  in  mind  that  these  numbers  do  not 
represent  the  quantities  of  oxygen  each  reagent  would  ab- 
sorb in  complete  combustion  ;  but  that  it  only  indicates 
the  quantity  of  metal  produced  by  equal  weights  of  the 
reagents. 

In  assaying,  however,  it  is  rarely  that  these  agents  are 
used  by  themselves ;  they  are  generally  mixed  with  a  flux 
properly  so  called,  which  will  be  more  particularly  de- 
scribed under  the  head  of  Fluxes. 

METALLIC  IRON  removes  oxygen  from  the  oxides  of  lead, 
bismuth,  copper,  &c.,  but  is  rarely  added  for  that  especial 
purpose  ;  and  when  it  does  produce  this  effect,  it  is  gener- 
ally secondary,  because  it  previously  existed  in  the  matter 
subjected  to  assay,  or  was  added  for  some  other  purpose. 


.             m 

• 

104-00 

.             . 

34-31 

aarcoal 

31-81 

.:        - 

30-00 

harcoal 

28-00 

.  '     .'. 

17-40 

•       •  •  • 

15-20 

•   '  -  •• 

14-50 

.        . 

14-50 

.        . 

13-00 

•  .      :  • 

11-50 

11-00 

6-00 

ate     . 

170 

•90 

170  OXIDISING   AGENTS. 

METALLIC  LEAD  reduces  but  a  very  small  number  of 
oxides,  but  it  reduces  many  to  the  minimum  of  oxidation  ; 
it  also  decomposes  some  sulphates  and  arseniates. 


II.    OXIDISING   AGENTS. 

The  oxidising  agents  in  general  use  are  as  follows  : — 

1.  Oxygen,  atmospheric  or  combined. 

2.  Litharge  and  ceruse. 

3.  Lead  silicates  and  borates. 

4.  Potassium  nitrate. 

5.  Lead  nitrate. 

6.  Manganese  peroxide. 

7.  Copper  oxide. 
8  Iron  peroxide. 

9.  The  caustic  alkalies. 

10.  The  alkaline  carbonates. 

11.  Lead,  copper,  and  iron  sulphates. 

12.  Sodium  sulphate. 

OXYGEN  is  a  gas  which  has  neither  smell  nor  taste,  and 
is  about  one-tenth  heavier  than  atmospheric  air.  It  has 
the  property  of  forming  compounds  with  nearly  every 
element,  and  its  affinities  are  very  energetic.  Atmospheric 
air  consists  of  four-fifths  nitrogen  and  one-fifth  oxygen. 

LITHARGE  is  a  fused  protoxide  of  lead,  and  is  generally 
obtained  from  the  silver-lead  works.  When  melted,  it 
oxidises  nearly  all  the  metals,  except  mercury,  silver,  gold, 
palladium,  platinum,  &c.,  and  generally  forms  very  fusible 
compounds  with  the  oxides.  These  two  properties  cause 
it  to  be  a  very  valuable  agent  in  separating  silver  and 
gold  from  all  the  substances  with  which  they  may  be 
mixed. 

Litharge  is  occasionally  mixed  with  a  little  of  the  red 
oxide  of  lead  ;  the  presence  of  this  in  large  quantities  be- 
comes injurious,  as  it  has  the  property  of  oxidising  silver. 
Ordinary  litharge  can  be  easily  freed  from  this  oxide  by 
fusing  it  and  pouring  it  into  a  cold  ingot  mould,  then 


ACTION    OF    OXIDE    OF    LEAD    UPON    VARIOUS   METALS       171 

pulverising,  and  carefully  keeping  it  from  contact  with  air, 
as  it  readily  absorbs  oxygen,  and  if  it  be  allowed  to  cool  in 
the  atmosphere  it  will  nearly  all  be  converted  into  the  red 
oxide. 

CERUSE,  or  WHITE  LEAD,  is  a  carbonate  of  lead  protoxide. 
As  it  does  not  contain  the  slightest  traces  of  red  oxide,  it 
may  be  used  where  the  presence  of  that  substance  may  be 
inconvenient ;  but  it  is  troublesome  to  use,  as  it  is  much 
less  dense  than  litharge  ;  large  vessels  must  be  employed 
in  consequence ;  besides,  it  generally  contains  a  small 
quantity  of  lead  acetate  or  subacetate,  and  sometimes 
metallic  lead  separates  from  it  on  ignition,  which  is,  in 
some  cases,  disastrous  to  the  result  of  an  experiment. 
When  ceruse  is  employed,  a  certain  quantity  must  be  fused, 
to  ascertain  if  any  metallic  lead  be  produced  ;  and,  on  the 
other  hand,  it  must  be  examined  to  ascertain  if  it  be  adul- 
terated with  barium  sulphate.  When  it  is  pure,  it  dissolves 
completely  in  acetic  or  nitric  acid. 

ACTION  OF  OXIDE  OF  LEAD  ON  THE  METALS. —  The  following 
are  the  results  of  the  experiments  of  Berthier  on  the  action 
exercised  by  oxide  of  lead  on  sulphur,  selenium,  tellurium, 
arsenic,  and  the  most  common  of  the  metals.  The  experi- 
ments were  made  in  a  furnace  capable  of  producing  heat 
enough  for  a  copper  assay. 

SULPHUR. — Lead  oxide  is  completely  reduced  by  sulphur 
with  the  formation  of  sulphurous  acid,  but  not  a  trace  of 
sulphuric  acid:  thus  S  +  2PbO  =  2Pb  +  S02. 

SELENIUM  is  dissolved  by  oxide  of  lead  in  all  propor- 
tions ;  but  these  bodies  exercise  no  action  on  each 
other. 

TELLURIUM  is  strongly  attacked  and  converted  into  tel- 
luric acid,  which  combines  with  the  oxide  of  lead  when 
the  latter  is  in  excess  (Te  +  4PbO  =  3Pb  +  PbO,Te03) .  If  the 
contrary  be  the  case,  the  excess  of  acid  is  volatilised  and 
telluride  of  lead  produced  (2Te  +  3PbO  =  TePb3-fTe03). 

ARSENIC. — When  metallic  arsenic  is  heated  with  litharge, 
if  the  latter  be  employed  in  great  excess,  all  the  arsenic  is 
oxidised  (As2  +  3PbO  =  As203  +  3Pb)  ;  if  not,  a  part  only  is 
oxidised,  and  lead  produced  ;  the  remainder  volatilises,  or 


172  ACTION   OF    OXIDE    OF    LEAD 

forms  a  lead  arsenide.  (For  nature  of  reaction,  refer  to 
the  preceding  metal,  Tellurium.)  Mixtures  of 

Arsenic     .     -    .-      .     75-24  3760  9-40 

Litharge  .        ..  .      .  111-60  111-60  111-60 

gave :  No.  1,  a  lamellar  metallic  button,  and  a  compact 
vitreous  slag  of  a  fine  orange-colour.  The  fusion  was  ac- 
companied by  a  considerable  amount  of  arsenical  smoke. 

No."  2  gave  a  semi-ductile  metallic  button,  with  a 
lamellar  fracture,  like  galena,  but  not  so  blue,  and  a  trans- 
parent vitreous  orange-coloured  slag. 

No.  3  yielded  a  button  of  lead  and  a  deep  olive- 
green  slag,  very  crystalline,  and  in  large  plates.  This 
fusion  was  not  accompanied  by  smoke.  It  is  probable 
that  arsenious  acid  is  formed  in  these  reactions :  the  last 
slag  contained  about  a  fifth  of  its  weight  of  this  acid. 

Lead  reduces,  in  part,  arsenious  acid  ;  in  the  same 
manner,  arsenic  partly  reduces  oxide  of  lead.  A  mix- 
ture of 

Arsenious  acid      ......  12*40 

Lead    .        .        .     '    .  ''    .        .        .        .  38-80 

produced  on  fusion  a  very  arsenical  vapour,  and  yielded 
32  parts  of  arsenide  of  lead,  which  was  deep-grey,  semi- 
ductile,  and  had  a  granular  fracture  ;  a  fine  orange-yellow 
vitreous  lead  arsenite  was  also  produced. 

ANTIMONY. — The  two  following  mixtures  of  antimony 
and  litharge : — 

Antimony    .         .         .         .         .  10  10 

Litharge 40  80 

gave  (No.  1)  23  parts  of  lead,  and  a  compact,  well-fused 
slag,  of  a  topaz  yellow  colour,  which  contained  more  than 
one-third  of  its  weight  of  antimony  protoxide  (Sb  -f  3PbO 
=  Sb03  +  3Pb).  The  second  gave  26  parts  of  lead,  and  a 
very  fluid  glass,  which  cooled  rapidly,  and  was  opaque, 
like  yellow  wax  ;  it  contained 

Lead  oxide  .         ...        .        .         .52 

Antimony  protoxide      .         .         .         .         .  11*86 

TIN. — This  metal,  cut  into  small  fragments,  was  heated 
with  the  following  quantities  of  litharge  :  — 

Tin     .         .         .         .  10  10  10 

Litharge     .         .         .  37'5  80  120 


UPON   VAKIOUS   METALS.  173 

The  first  mixture  gave  a  slaggy  substance,  of  dull  grey 
colour,  not  well  fused,  with  globules  of  lead  at  the  lower 
part. 

The  second  mixture  gave  26  parts  of  lead,  and  a  semi- 
fused  slag,  compact  and  opaque,  the  colour  yellowish-grey. 
It  contained 

Lead  oxide         .         .         .         .         .         .         .52 

Tin  protoxide 11-4 

The  third  mixture  produced  26 -3  of  lead,  and  a  very 
fluid  slag,  which  was  compact,  opaque,  and  greyish-yellow 
with  a  granular  fracture  (Sn  +  PbO  =  SnO-l-Pb).  It  con- 
tained 

Lead  oxide 97 '0 

Tin  oxide 11-4 

ZINC. — Ten  parts  of  zinc  filings  and  100  of  litharge 
were  heated  together  ;  as  soon  as  the  latter  softened,  action 
commenced.  A  slight  bubbling  and  flaming,  occasioned 
by  the  combustion  of  a  portion  of  the  zinc,  took  place, 
and  on  increasing  the  heat  the  mixture  fused  completely. 
The  result  was  a  button  of  lead  equal  to  13  parts  ;  it  was 
pure  and  ductile,  and  was  covered  with  a  crystalline  slag, 
like  litharge,  opaque  and  yellowish,  but  in  small  plates. 
This  experiment  proves  that  about  one-fifth  of  the  zinc 
employed  is  volatilised,  whilst  the  remainder  reduces  the 
litharge  (Zn  -r  PbO = ZnO  +  Pb) .  The  slag  contains 

Lead  oxide 877 

Zinc  oxide 123 

BISMUTH. — Twenty  parts  of  bismuth  heated  with  40  of 
litharge  gave  a  ductile  metallic  button,  tin-white,  and 
weighing  24*3  parts,  and  a  crystalline  slag,  like  litharge. 

IRON. — M.  Berthier  heated  metallic  iron  with  litharge 
in  the  following  proportions- 
Iron  wire          ....     10  10 
Litharge 100                     160 

The  first  mixture  gave  40  of  lead,  and  a  pasty,  com- 
pact, opaque  slag  of  a  deep  metallic-black  colour,  and  very 
magnetic  (Fe  +  PbO=FeO  +  Pb).  There  was  no  metallic 


174       ACTION   OF    OXIDE    OF    LEAD   UPON    VARIOUS    METALS. 

iron,  but  some  globules  of  lead  were  present.     The  slag 
contained  about 

Lead  oxide     .         .  '      ,      ~ .  •      .         .         .  55*9 

Iron  oxide       .         .        ..,,«.     •   .'        .  13'4 

The  second  mixture  gave  a  button  of  lead,  weighing 
46-6,  and  a  very  fluid,  compact,  opaque  slag,  with  an  un- 
equal shining  lustre,  deep-brown,  and  very  magnetic.  The 
slag  contained  nearly 

Lead  oxide    .        .        .    Y-4-.  ••  \  *   -     •         •  110 
Iron  oxide     .         .  '      .        .     ;    .-      .         .     13'4 

COPPER. — The  following  are  the  results  obtained  with 
different  mixtures : — 

Copper        .        .  15-8        15-8        15-8          15-8          15-8 
Litharge      .         .  13-9        27'9        55-8         167'4        334-8 

With  the  first  mixture  a  button  was  produced,  copper- 
red  on  the  exterior,  grey  in  the  interior,  weighing  17 
parts ;  and  a  compact,  opaque,  deep-red  slag.  The  slag 
contained 

Lead  oxide      .         .         .         .       ....         .  10-3 

Copper  suboxide      .         .         .        .        -.        •    2'4 

and  the  button — 

Copper 13-6 

Lead       .         .         .'        4      ,-.  :      v     :>i;i    .'    3-4 

The  button  produced  by  the  second  mixture  was  ex- 
teriorly copper-red,  and  interiorly  grey,  spotted  with  red  ; 
it  weighed  17*8,  and  the  slag  was  compact,  reddish-brown, 
and  opaque.  The  slag  contained 

Lead  oxide      .         .         .         .         ...       .  22-3 

Copper  suboxide      ......     3*6 

and  the  button — 

Copper   .         .         .         .        .  .  12-4 

Lead -'       .     5-2 

The  third  mixture  gave  a  button  similar  to  the  last, 
weighing  18  parts,  and  a  compact,  opaque,  reddish-brown 
slag.  It  contained 

Lead  oxide     .         .         .         ...         .  49-8 

Copper  suboxide     .         .        ,",,..     3'8 


The  button  was  composed  of 


.  12-4 

5-6 


ACTION   OF   COPPER   OXIDES.  175 

With  the  fourth  mixture,  a  button  weighing  25- 6  was 
produced,  and  a  slightly  crystalline,  reddish -brown  slag, 
which  contained 

Lead  oxide 151-28 

Copper  suboxide  .....     10'32 

and  with  the  fifth,  a  grey  metallic  button,  weighing  23- 6  r 
and  a  crystalline  slag  in  large  plates,  like  litharge,  yellow- 
ish green  and  reflecting  green.  The  analysis  of  the  button 

gave  Copper    .  3-6 

Lead      .        .        .        .        .        .         .        .  2OO 

and  the  slag  contained 

Lead  oxide 313-28 

Copper  suboxide 13-72 

ACTION  OF  COPPER  OXIDES  UPON  LEAD. — Copper  oxide  is 
speedily  reduced  to  the  state  of  suboxide  by  excess  of  lead. 
If  the  lead  be  not  in  excess,  it  is  totally  oxidised,  reducing 
a  corresponding  quantity  of  the  copper  to  the  minimum  of 
oxidation. 

The  oxide  is  reduced  to  the  metallic  state  by  lead,  but 
not  completely,  because  a  certain  quantity  is  taken  up  by 
litharge.  The  following  mixtures  have  been  made  the 
subject  of  experiment : — 

Metallic  lead  .         .  25-9        25-9        25-9        38-8        51-8 

Copper  suboxide     .         .  19*8         14'9          9-9          9-9          9'9 

All  of  these  gave  an  imperfect  alloy  of  copper  or  lead, 
and  a  very  fusible  slag  composed  of  lead  oxide  and  copper 
suboxide.  The  first  produced  a  very  small  globule  of 
copper  and  a  very  fluid  slag,  having  a  much  greater  ten- 
dency to  run  through  the  body  of  a  crucible  than  litharge. 
Cooled  slowly,  it  was  reddish-brown,  opaque,  and  had  a 
finer  texture.  It  was  composed  of 

Lead  oxide 27*9 

Copper  suboxide 17-8 

The  second  mixture  produced  a  button  of  copper  weigh- 
ing 4-4,  and  a  deep  reddish-brown  slag,  composed  of 

Lead  oxide 27-7 

Copper  suboxide      .  .     8'7 

The  button  gave — 

Copper 4-1 

Lead 0-3 


176  OXIDISING   FLUXES. 

The  third  gave  a  metallic  button  weighing  8 -8,  and  a 
deep  red,  opaque  slag,  which  contained 

Lead  oxide   .         .         .        .-„•,       •         •         •  24-89 
Copper  suboxide  .         .         .      ,  ,        .         .     2-ll 

The  button  contained 

Copper  .         .         .        ,    '  V       .      ;  .         •     6*9 
Lead      .        .        /       .  --.'.;.-  -\    v        .        .    2'9 

In  the  fourth  and  fifth  mixtures,  buttons  weighing  21-2 
and  84*8  were  produced,  together  with  slags  similar  to  the 
preceding,  and  containing  about  1  per  cent,  of  copper  sub- 
oxide. 

LEAD  SILICATES  AND  BORATES  behave  as  litharge,  but  they 
oxidise  less  rapidly. 

They  may  be  prepared  by  fusing  together  1  part  of 
silica  or  boracic  acid  with  1  part  of  litharge.  The  borates 
are  more  fusible  than  the  silicates,  but  their  use  is  attended 
with  inconvenience,  as  they  swell  very  much  in  fusing. 

POTASSIUM  AND  SODIUM  NITEATES  fuse  at  a  temperature 
below  redness,  without  alteration,  but  when  heated  more 
strongly  they  give  up  oxygen.  The  action  of  these  salts, 
when  fused,  is  very  energetic,  because  they  have  a  great 
tendency  to  decompose,  and  because  they  contain  a  large 
quantity  of  oxygen.  They  are  used  as  oxidising  agents  in 
the  purification  of  the  noble  metals,  and  for  preparing 
some  fluxes.  They  ought  always  to  be  employed  in  a 
state  of  purity. 

Saltpetre  often  contains  impurities.  On  this  account 
a  determination  of  the  real  amount  of  potassium  nitrate 
often  becomes  necessary,  not  only  in  cases  where  saltpetre 
is  to  be  used  for  docimetric  purposes,  but  also  when  used 
in  certain  technical  operations,  viz.  the  manufacture  of 
gunpowder,  enamel,  &c. 

If  saltpetre  is  very  impure,  it  may  easily  be  purified 
by  recrystallisation  to  such  a  degree  that  it  will  only  con- 
tain 2  to  3  per  cent,  foreign  substances  (chiefly  sodium 
chloride). 

An  exact  assay  of  saltpetre  is  most  difficult,  and  the 
different  modes  in  use  are  not  quite  accurate,  on  account 
of  the  chemical  properties  of  the  nitric  acid,  potash,  and 


IMPURITIES   IN   SALTPETRE.  177 

soda,  which  substances  are  generally  contained  together  in 
saltpetre,  and  cannot  be  perfectly  estimated  by  means  of 
reagents.  This  is  chiefly  the  case  with  the  nitric  acid  and 
soda. 

Soda  is  frequently  found  in  saltpetre,  as  the  manufac- 
turers often  intentionally  mix  the  raw  saltpetre  with  soda- 
saltpetre,  and  it  is  also  often  manufactured  from  a  mixture 
of  soda-saltpetre  and  potassium  carbonate. 

ASSAY  OF  SALTPETRES. — The  following  are  the  different 
modes  of  assaying  saltpetre. 

a.  To  determine  the  nitric  acid  directly,  150  grains  of 
the  well-ground  sample  are  mixed  with  six  times  the  weight 
of  well-powdered  silica,  placed  in  a  platinum  capsule  and 
dried  in  the  water-bath  till  there   is  no  further  loss  of 
weight.     The  temperature  is  then  raised  to  dull  redness 
for   about  half  an   hour,    by   which    the  whole   of  the 
nitric  acid  is  expelled.     Its  quantity  is  found  by  weighing 
the  cold  crucible. 

Sodium  nitrate  may  be  treated  in  the  same  manner. 

The  most  usual,  though  not  the  most  satisfactory,  pro- 
cess for  the  assay  of  potassium  and  sodium  nitrates  is  to 
determine  the  total  impurities,  viz.  water,  insoluble  matter, 
alkaline  chlorides  and  sulphates,  and  the  residue  being- 
taken  as  pure  nitrate. 

b.  GAY-LUSSAC'S  MODE  of  assaying  saltpetre  consists  in 
converting  the  potassium  nitrate  into  potassium  carbonate, 
and  in  determining  its  amount  volumetrically  by  means  of 
standard  sulphuric  acid.     2-639  grs.  of  saltpetre  are  mixed 
with  1  gr.  of  ignited  pine-root,  and  12  grs.  of  ignited  and 
finely  pulverised  sodium  chloride  (the  latter  is  added  in 
order  to  moderate  the  combustion),  and  this  mixture  is 
heated  in  a  platinum  crucible.     After  cooling,  the  mass  is 
extracted  by  water,  and  either  a  standard  solution  of  sul- 
phuric acid  or  oxalic  acid  is  added  to  the  solution.     The 
sulphuric  acid  is  prepared  by  mixing  70  grs.  of  sulphuric 
acid,  sp.  gr.  1*84,  with  600  grs.  of  water,  and  to  this  mixture 
so  much  water  is  added  again  that  100  measures  of  it  will 
saturate  6,487  grs.  of  potassium  carbonate.  The  number  of 


178  ASSAY    OF   SALTPETRE. 

measures  used  for  saturation  will  then  indicate  directly 
the  percentage  of  potassium  carbonate. 

The  following  foreign  substances  in  raw  saltpetre 
should  be  determined. 

Water. — Twelve  to  20  grammes  of  air-dried,  finely 
pulverised  saltpetre  are  heated  in  a  porcelain  crucible  to 
120°  C.,  and  the  resulting  loss  is  calculated  as  water. 

Mechanically  mixed  Impurities. — The  substance  ob- 
tained in  the  former  assay  is  dissolved  in  hot  water,  and 
filtered  through  a  dried  and  weighed  filter.  The  residue 
is  well  washed  with  hot  water,  dried  on  the  filter  at 
120°  C.,  and  weighed.  On  deducting  the  weight  of  the 
filter,  there  will  be  left  the  weight  of  the  mechanically 
mixed  impurities  (alumina,  silica,  calcium  carbonate,  iron 
peroxide,  &c.),  which  usually  amount  to  2  to  5  per  cent. 

Lime  and  Magnesia. — These  substances  are  precipitated 
as  carbonates,  in  the  former  filtered,  solution  raised  to  the 
boiling-point,  by  sodium  carbonate ;  the  carbonates  are 
then  dissolved  in  hydrochloric  acid,  and  neutralised  with 
ammonia.  The  lime  can  be  precipitated  by  oxalic  acid, 
and  filtered  off ;  the  magnesia  which  remains  in  solution 
may  then  be  precipitated  by  sodium  phosphate. 

The  amount  of  lime  in  East  Indian  raw  saltpetre  which 
has  been  once  crystallised  varies  between  0*216  and  0-265 
per  cent.,  the  amount  of  magnesia  between  0-263  and  0'28 
per  cent. 

Chlorine. — Two  to  3  grammes  of  raw  saltpetre  are  dis- 
solved in  about  30  grammes  pure  warm  water,  in  a  flask 
furnished  with  a  tight-fitting  stopper,  and  the  amount  of 
chlorine  is  determined  by  a  standard  solution  of  nitrate  of 
silver.  The  latter  is  prepared  by  dissolving  4*793  grammes 
of  silver  nitrate  in  1,000  burette  divisions  of  water  ;  each 
division  of  the  burette  will  then  indicate  0*001  gramme  of 
chlorine.  The  solution,  after  being  warmed  and  acidulated 
with  nitric  acid,  is  mixed  gradually  with  the  solution  of 
silver  ;  after  each  addition  of  the  latter,  it  is  to  be  shaken 
and  then  allowed  to  rest. 

The  amount  of  chlorine  determined  by  this  assay  is 
calculated  as  being  derived  from  §  potassium  chloride,  and 


ASSAY   OF   SALTPETRE.  179 

^  sodium  chloride,  so  that  1  part  of  chlorine  corresponds 
to  1-927  part  of  metal  (1-285  potassium,  0*642  sodium). 
Experience  has  proved  that  East  Indian  saltpetre  contains 
potassium  and  sodium  chloride  in  these  proportions. 

Sulphuric  Acid. — Six  to  8  grammes  of  raw  saltpetre 
are  dissolved,  and  from  this  solution  diluted  and  heated 
to  the  boiling-point,  the  sulphuric  acid  is  precipitated  by 
means  of  a  standard  solution  of  baryta.  By  using  a  solu- 
tion of  3-26  grammes  of  barium  nitrate  in  2,000  parts  of 
the  burette,  each  division  of  the  latter  will  correspond  to 
0-0005  gramme  sulphuric  acid.  The  amount  of  sulphuric 
acid  in  East  Indian  raw  saltpetre  varies  between  0*05  and 
0-11  per  cent. 

Sodium  Nitrate. — This  determination  is  most  difficult, 
and  the  following  modes  are  recommended. 

a.  Perfectly  pure  potash-saltpetre  is  mixed  with  differ- 
ent quantities  of  soda-saltpetre.  These  mixtures  are  put 
under  a  glass  bell-jar,  together  with  a  quantity  of  the  raw 
saltpetre  to  be  assayed.  The  glass  bell  must  contain  also 
a  vessel  with  water.  After  a  certain  time,  it  is  ascertained 
which  of  the  standard  samples  corresponds  in  weight  with 
the  raw  saltpetre. 

The  results  so  obtained  are  of  value  only  if  no  other 
hygroscopic  salts  (magnesium,  chloride,  &c.)  are  present. 

j3.  Longchamps'  mode  is  based  upon  the  decomposition 
of  soda-saltpetres  by  potassium  chloride,  producing  sodium 
chloride  and  potassium  nitrate.  The  saltpetre  is  mixed 
with  potassium  chloride,  and  the  solution  evaporated 
down.  By  this  operation,  first  sodium  chloride  and  after- 
wards saltpetre  become  separated.  The  latter  is  washed, 
dried  at  150°  C.,  and  weighed.  Werther  has  recommended 
a  similar  mode. 

If  the  saltpetre  does  not  contain  certain  oxides,  such 
as  alumina,  lime,  &c.  (or  if,  previously  present,  they  have 
been  precipitated),  a  solution  of  potassium  antimoniate 
will  precipitate  the  soda  contained  in  the  saltpetre  solution. 
The  precipitate  consists  of  sodium  antimoniate,  100 
parts  of  which  contain  84-39  antimonious  acid,  and  15-61 
soda 


180  ASSAY    OF   SALTPETKE 

The  presence  of  soda  is  also  to  be  ascertained  by 
washing  saltpetre  with  a  saturated  solution  of  pure  potash- 
saltpetre.  This  saturated  solution  will  then  contain  a 
proportionally  large  amount  of  sodium  nitrate.  If  a  small 
quantity  of  the  solution  is  made  to  crystallise  upon  a 
watch  glass,  soda-saltpetre,  showing  a  rhombohedric  formr 
may  be  detected  by  means  of  a  microscope,  while  potash - 
saltpetre  crystallises  in  prisms,  and  sodium  and  potassium 
chlorides  in  cubes  arranged  in  the  form  of  steps. 

Soda-saltpetre  (Chili-  or  cubic-saltpetre)  may,  in  many 
cases,  be  substituted  for  potash-saltpetre. 

LEAD  NITRATE  acts  in  a  similar  way  to  the  two  last- 
mentioned  salts.  It  is  prepared  by  dissolving  litharge  in 
nitric  acid,  and  crystallising  the  solution. 

MANGANESE  PEROXIDE  is  easily  reduced  to  the  state  of 
protoxide  by  many  metals,  and  is  a  very  powerful  oxidis- 
ing agent ;  but  is  rarely  employed,  because  its  compounds 
are  very  infusible.  It  is  employed  occasionally  in  the 
purification  of  gold  and  silver. 

COPPER  OXIDE  is  not  much  employed  as  a  flux,  but  is 
often  contained  in  substances  submitted  to  assay  ;  it  then 
acts  as  an  oxidising  agent.  A  great  number  of  metals, 
even  silver,  reduce  it  to  the  minimum  of  oxidation :  and 
other  metals,  as  iron,  for  instance,  totally  reduce  it. 

IRON  PEROXIDE. — This,  like  copper  oxide,  sometimes  acts 
incidentally  as  an  oxidising  agent. 

THE  CAUSTIC  ALKALIES,  POTASH  AND  SODA,  fuse  below  a 
red  heat,  and  volatilise  sensibly  at  a  higher  temperature. 
Charcoal,  at  a  high  temperature,  decomposes  the  .water 
combined  with  the  hydrates  of  potash  and  soda,  con- 
verting them  into  carbonates,  but  an  excess  at  a  white 
heat  decomposes  the  carbonate,  and  potassium  or  sodium 
is  the  product. 

POTASSIUM  AND  SODIUM  CARBONATES  are  very  much  em- 
ployed as  agents  in  the  assay  by  the  dry  way.  They 
have  the  power  of  oxidising  many  metals,  as  iron,  zinc, 
and  tin,  by  the  action  of  the  carbonic  acid  they  contain ; 
part  of  it  being  decomposed,  with  the  formation  of  car- 
bonic oxide. 


DESULPHURISING   REAGENTS.  181 

LEAD,  COPPER,  AND  IRON  SULPHATES. — These  three  salts  at 
a  high  temperature  oxidise  the  greater  number  of  the 
metals,  even  silver,  the  sulphuric  acid  giving  off  oxygen 
and  sulphurous  acid.  They  are  used  in  the  assay  of  gold. 

SODIUM  SULPHATE  is  not  used  by  itself  as  a  reagent,  but 
is  a  product  in  many  operations  ;  it  is  either  formed  in 
the  course  of  an  assay,  or  is  contained  as  an  impurity  in 
some  of  the  bodies  used. 

III.    DESULPHURISING   REAGENTS. 

1.  The  oxygen  of  the  atmosphere. 

2.  Charcoal. 

3.  Metallic  iron. 

4.  Litharge. 

5.  The  caustic  alkalies. 

6.  The  alkaline  carbonates. 

7.  Nitre. 

8.  Lead  nitrate. 

9.  Lead  sulphate. 

1.  THE  OXYGEN  or  THE  ATMOSPHERE  acts  as  a  desulphuris- 
ing agent  in  roasting,  combining  with  the  sulphur  present, 
forming   sulphurous   acid  (2FeS2  +  110=Fe2034.4S02)   or 
sulphuric  acid  (CuS  +  40==CuO,S03),  sometimes  both. 

2.  CHARCOAL   decomposes  many   sulphides   by   taking 
their  sulphur  to  form  sulphide  of  carbon.     It  acts  in  this 
manner  with  the  mercury,  antimony,  and  zinc  sulphides 
(2ZnS  +  C=2Zn  +  CS2)..    It  is  only  employed  as  an  auxi- 
liary to  the  desulphurising  power  of  the  alkalies  and  their 
carbonates. 

3.  IRON   separates  sulphur   from   lead   (PbS-f-Fe=Pb 
•f  FeS),  silver,  mercury,  bismuth,  zinc,  antimony,  and  tin, 
but   only  partially  decomposes   copper   sulphide.     It   is 
generally  used  in  the  state  of  filings,  or  nails  ;  the  latter 
are   preferable,  and    ought  .to   be   kept   free  from  rust. 
Oxide   of  iron   may  be  used   if  it  be   mixed  with   the 
requisite  quantity  of  charcoal  to   reduce   it.     Cast   iron 
must  not  be  employed,  as  it  has  very  little  affinity  for 
sulphur. 


182  LITHARGE. 

4.  LITHARGE  (PbO)  exercises  a  very  energetic  action  on 
sulphides,  even  at  a  low  temperature.  If  it  be  employed 
in  sufficient  proportion,  the  sulphide  acted  on  is  wholly 
decomposed.  The  sulphur  is  often  disengaged  as  sulphur- 
ous acid,  and  the  metal  remains  alloyed  with  the  lead 
proceeding  from  the  reduction  of  a  portion  of  the  litharge, 
or  combines  as  oxide  with  that  portion  of  the  litharge 
which  is  not  reduced.  The  quantity  of  litharge  requisite 
for  the  decomposition  of  a  sulphide  is  considerable,  and 
varies  according  to  its  nature  ;  some  sulphides  require 
34  times  their  weight.  When  less  than  the  requisite 
quantity  is  used,  only  a  portion  of  the  sulphide  is 
decomposed,  and  a  corresponding  quantity  only  of  lead 
reduced,  whilst  the  remainder  of  the  sulphide  forms,  with 
the  litharge  and  the  metallic  oxide  which  can  be  produced , 
a  compound  belonging  to  the  class  of  oxysulphides,  which 
is  generally  very  fusible. 

When  the  sulphides  have  a  very  strong  base,  as  an 
alkali  or  alkaline  earth,  no  sulphurous  acid  is  given  off  by 
the  action  of  litharge,  but  all  the  sulphur  is  converted  into 
sulphuric  acid. 

Litharge  is  a  very  valuable  reagent,  and  its  use  is 
nearly  exclusively  confined  to  the  assay  of  sulphides 
containing  the  noble  metals,  as  these  metals  are  thus 
obtained  as  alloys  of  lead,  which  are  afterwards  assayed 
by  cupellation. 

The  following  is  an  account  of  the  behaviour  of  this 
reagent  with  the  ordinary  sulphides. 

Manganese  Sulphide  requires  at  least  six  times  its 
weight  of  litharge  to  produce  a  fusible  compound,  and 
thirty  times  its  weight  to  desulphurise  it  completely. 
The  sulphur  and  metal  oxidise  simultaneously  (MnS 
-f  3PbO=MnOS02-h  3P  b),  and  a  manganese  protoxide  is 
formed,  which  partly  peroxidises,  taking  a  brownish  tint  in 
contact  with  the  atmosphere.  Berthier  assayed  the  four 
following  mixtures : — 

Manganese  sulphide  .     5          55  5 

Litharge       .       ,v    -  ,*  i ,   ;,  20        30         100        150 

The  first  produced  an  infusible,  greyish -black,  scori- 


LITHARGE.  183 

form  mass,  in  which  small  plates,  having  the  look  of 
galena,  could  be  discovered.  It  was  composed  of  the 
sulphides  and  oxides  of  manganese  m  and  lead.  Much 
sulphurous  acid  was  given  off  during  the  operation. 

The  second  fused  to  a  soft  paste,  and  gave  17*5  of 
lead,  and  a  compact,  vitreous,  opaque  slag,  of  a  very  deep 
brown  colour.  The  slag  contained  about  half  its  weight 
of  manganese  sulphide. 

The  third  fused  readily,  and  produced  31/5  of  ductile 
lead,  and  a  transparent,  vitreous  slag,  of  a  deep  hyacinth 
red. 

The  fourth  produced  33-7  of  lead,  exceedingly  ductile, 
and  the  desulphurisation  was  complete. 

Iron  Sulphide. — -Thirty  parts  of  litharge  are  sufficient 
to  scorify  iron  protosulphide  ;  the  metal  is  converted  into 
the  protoxide  (FeS  +  3PbO=FeO  +  Se2  +  3Pb). 

The  four  following  mixtures — 

Iron  protosulphide     ...  10  10          10          10 

Litharge 60        125        250        300 

gave,  the  first  a  pasty,  scoriform  mass,  colour  metallic 
grey,  and  very  magnetic.  It  was  composed  of  the  sul- 
phides and  protoxides  of  iron  and  lead. 

The  second  gave  a  very  fluid  metallic  black  slag,  very 
magnetic,  opaque,  and  possessing  great  lustre,  and  36  of 
lead. 

The  third  gave  a  compact  vitreous  transparent  slag  of 
a  fine  resin-red,  and  67  of  lead. 

The  last  yielded  a  similar  slag  to  the  former,  but  con- 
taining no  sulphur,  and  70  of  lead. 

Native  iron  pyrites  was  treated  with  the  following 
proportions  of  litharge  : — 

Iron  pyrites      .         .  10          10          10          10          10          10 
Litharge  ..  60        125        200        300        400        500 

The  mixtures  fused  very  readily  with  an  abundant 
disengagement  of  sulphurous  acid. 

The  first  produced  only  a  metallic  button,  divisible 
into  two  parts  :  the  lower  was  the  largest,  and  was  a  lead 
subsulphide;  the  other  looked  like  the  compact  galena, 
but  was  magnetic ;  it  was  composed  essentially  of  the 


184  ACTION   OF    LITHARGE   ON   SULPHIDES. 

sulphides  of  iron  and  lead,  but  probably  contained  a  small 
quantity  of  their  oxides. 

The  second  and  third  gave  black  vitreous  opaque 
slags  which  stained  the  crucibles  brown,  together  with 
lead,  having  a  granular  fracture,  and  a  deep  grey  colour : 
the  first  button  weighed  35,  and  the  second  40.  Both 
samples  of  lead  were  contaminated  with  a  small  quantity 
of  slag,  and  contained  from  T^¥ths  to  y^th  of  sulphur, 
and  a  small  quantity  of  iron. 

The  slags  from  the  three  last  mixtures  were  vitreous, 
transparent,  and  of  a  fine  resin-red  colour  :  the  buttons  of 
lead  weighed  45'4,  54*8,  and  86  parts.  A  much  larger 
proportion  of  litharge  does  not  produce  more  than  86  of 
lead,  proving  that  50  parts  of  litharge  completely  effect 
the  desulphurisation  of  iron  pyrites. 

Copper  Sulphide. — The  following  mixtures  of  sulphide 
of  copper  and  litharge — 

Copper  sulphide         .         .  10         10         10          10          10 
Litharge    .         ..        .         .  20        30        50        100        250 

fuse  very  readily,  giving  off  an  abundance  of  sulphurous 
acid. 

The  slags  formed  were  compact,  vitreous,  opaque,  or 
translucid,  and  more  or  less  bright  red.  The  copper 
which  they  contained  was  at  the  minimum  of  oxidation. 

The  three  first  mixtures  gave  metallic  buttons,  com- 
posed of  uncombined  lead  and  sulphide  of  copper. 

The  fourth  gave  28  of  lead,  with  a  little  adhering 
sulphide  of  copper. 

The  fifth  gave  38*5  of  pure  ductile  lead,  the  exact 
quantity  that  ought  to  be  reduced  from  litharge  by  the 
transformation  of  the  above  quantity  of  copper  sulphide 
into  suboxide  and  sulphurous  acid  (2CuS  +  5PbO  =  Cu20 
+  2S03+5Pb). 

Copper  sulphide  does  not  combine  with  litharge  ;  this 
is  an  exception  to  the  general  rule.  It  requires  about 
twenty-five  times  its  weight  of  litharge  to  decompose  it 
.completely.  When  litharge  is  combined  with  a  certain 
.quantity  of  copper  protoxide,  it  has  no  action  on  the 
sulphide  of  that  metal. 


ACTION   OF   LITHARGE    ON   SULPHIDES.  185 

The  desulphurisation  of  copper  pyrites  requires  about 
30  parts  of  litharge. 

Copper  pyrites    ....  10  10  10          10 

Litharge     ......  50        100        200        300 

were  fused  together. 

In  the  first  assay  the  fusion  was  accompanied  with 
much  ebulh'tion,  and  the  mass  remained  pasty  :  6  parts  of 
ductile  lead  were  produced,  and  a  matt  similar  to  galena, 
but  deep  grey,  with  small  facets,  and  a  brownish-black 
vitreous  slag. 

In  the  second,  much  ebullition  and  swelling  up  took 
place  :  35  of  lead,  45  of  matt,  and  a  deep  brown  vitreous 
slag,  were  produced. 

In  the  third  assay,  49  of  lead  was  the  result.  It  was 
covered  by  a  thin  layer  of  matt,  and  a  very  shining,  deep 
brown,  vitreous,  translucid  slag. 

The  last  mixture  fused  readily,  almost  without  ebul- 
h'tion, and  gave  72  of  lead,  and  a  compact  shining  slag,  of 
a  bright  grey,  and  without  the  least  trace  of  matt  ;  the 
desulphurisation  was  complete  (CuS,FeS  -f  6PbO  =CuO 


Antimony  Sulphide  has  a  great  tendency  to  combine 
with  litharge,  and  it  must  be  heated  with  at  least  25  parts 
to  effect  its  desulphurisation.  By  mixing  these  two  sub- 
stances in  the  following  proportions  :  — 

Antimony  sulphide  .  10         10  10  10  10 

Litharge          .         .         .38        00        100        140        250 

the  first  three  mixtures  afforded  very  fluid  slags,  compact, 
deep  black,  and  slightly  metallic,  and  buttons  of  ductile 
lead,  weighing  2,  9,  and  26  parts.  These  slags  resemble 
the  black  litharge  produced  at  the  commencement  of  a 
cupellation. 

The  fourth  mixture  gave  a  transparent  compact  slag, 
vitreous  and  shining,  having  a  splendid  hyacinth-red 
colour,  and  50  parts  of  lead. 

The  last  produced  57  of  lead,  proving  the  desulphuri- 
sation to  be  complete  (Sb2S3  +  9PbO  =  Sb203-f-3S02  +  9Pb). 
The  antimony,  in  this  case,  exists  as  protoxide  in  the  slag. 

M.  Fournet  has  observed  that  antimony  sulphide  has 


186  ACTION   OF   LITHAEGE   ON   SULPHIDES. 

the  property  of  carrying  copper  sulphide,  and  even  silver- 
sulphide,  into  the  compounds  formed  with  litharge.  In 
one  of  the  experiments  which  he  made,  a  double  sulphide, 
composed  of  equal  parts  of  silver  sulphide  and  antimony 
sulphide,  was  fused  with  three  times  its  weight  of  litharge, 
and  gave,  first,  a  button  of  lead,  mixed  with  silver ; 
secondly,  a  matt  like  galena  ;  and  thirdly,  a  black  slag. 
This  slag  was  analysed,  and  found  to  contain  from  8  to  9 
per  cent,  of  silver. 

It  is  probable  that  all  the  sulphides,  having  a  strong 
tendency  to  combine  with  lead  oxide,  have,  like  antimony 
sulphide,  the  property  of  determining  the  scorification; 
of  a  certain  quantity  of  silver  sulphide ;  like  all  the  sul- 
phides, which,  in  a  state  of  purity,  are  completely  decom- 
posed by  lead  oxide. 

Zinc  Sulphide  must  be  fused  with  twenty-five  times  its 
weight  of  litharge  to  be  decomposed.  The  following  mix- 
tures were  heated  together  : — 

Blende        .        .        .  .      .  24-08        12-08          10          10 
Litharge     ....  55-78        83-68         100        250 

However  strongly  the  first  mixture  was  heated,  it 
always  remained  pasty  ;  29*2  of  a  greyish-black  lead  were 
produced,  which  contained  -018  of  sulphur  and  -008  of 
zinc.  The  button  was  covered  by  a  metallic-looking  black 
substance,  intermediate  between  a  matt  and  a  slag ;  it 
was  composed  of  zinc  and  lead  sulphides  and  oxides. 

The  second  mixture  gave  35*5  of  lead  and  a  fluid  slag, 
which  was  compact,  opaque,  and  black. 

The  third  gave  43  of  lead,  and  a  deep  grey  slag. 

The  last  produced  65  of  pure  lead  (ZnS  +  3PbO  =  ZnO 
+  S02  +  3Pb),  and  a  vitreous  slag,  of  an  olive-colour,  and 
translucid  on  the  edges. 

Lead  Sulphide. — Galena  and  litharge,  at  a  heat  just 
sufficient  to  fuse  them,  combine  and  form  an  oxysulphide  ; 
but  if  the  temperature  be  increased,  the  two  bodies  react 
on  each  other,  and  are  mutually  decomposed  (PbS  +  2PbO 
=  3Pb  +  S02).  If  2,789  parts  of  litharge  be  employed  to 
1,496  of  lead,  or  1,865  of  litharge  to  1,000  of  galena, 
nothing  but  pure  lead  is  obtained.  If  more  litharge  be 


CAUSTIC    ALKALIES  AND   THEIR    CARBONATES.  187 

employed,  a  portion  is  not  decomposed,  and  covers  the 
lead.  If  less  be  employed,  the  galena  is  not  completely 
decomposed,  and  the  lead  is  covered  by  a  matt  of  sub- 
sulphide. 

But  when  litharge  is  combined  with  a  certain  pro- 
portion of  sulphides  or  metallic  oxides,  it  completely  loses 
its  oxidising  power  on  galena,  even  at  a  white  heat  ;  so 
that  it  can  be  combined  with  this  substance  as  with  the 
other  sulphides,  without  effecting  its  total  decomposition. 

5,  6.  CAUSTIC  ALKALIES  AND  THEIB,  CARBONATES. — All  the 
sulphides  are  decomposed  by  caustic  alkalies,  and  their 
carbonates ;  but  in  the  latter  case  carbonaceous  matter 
must  be  present.  In  the  absence  of  charcoal,  there  are 
some  sulphides,  as  of  copper,  on  which  they  have  no 
action.  In  these  decompositions  alkaline  sulphides  are 
formed,  and  combine  with  and  retain  a  certain  quantity 
of  the  sulphide  submitted  to  experiment.  The  proportion 
of  the  sulphide  which  remains  in  combination  with  the 
alkaline  sulphides  depends  on  many  circumstances.  It  is 
always  less  when  a  large  proportion  of  alkali  or  carbonate 
has  been  employed ;  as  it  is  also  when  a  high  degree  of 
temperature  has  been  employed  ;  and  the  presence  of 
charcoal  always  much  diminishes  the  proportion.  When 
the  metal  of  a  sulphide  is  very  volatile,  as  mercury  or 
zinc,  the  decomposition  may  be  perfect. 

Potash,  as  it  is  sold  in  commerce,  always  contains 
foreign  substances,  viz.  silica,  peroxide  of  iron,  potassium 
sulphate,  muriate,  phosphate,  and  silicate,  soda-salts,  &c.r 
and  also  water. 

A  partial  purification  of  the  potash  may  be  effected  by 
dissolving  it  in  boiling  water,  which  will  not  dissolve  some 
of  the  above-named  foreign  substances. 

The  amount  of  potassium  carbonate  contained  in 
potash  may  be  ascertained  by  a  standard  solution  of 
oxalic  acid,  or  by  tartaric  acid.  Mohr  *  recommends  for 
this  purpose  the  use  of  oxalic  acid. 

Soda  also  is  never  free  from  foreign  substances. 

*  Mohr,  Lehrb.  d.  Titriermetbode,  1855. 


188  NITRATE   OF   POTASH. 

The  determination  of  sodium  carbonate  may  be  effected 
also  by  tartaric  acid,  or  by  a  salt  of  oxalic  acid. 

When  employing  a  standard  solution,  sulphuric  acid  is 
taken,  or  sometimes  oxalic  acid,  while  for  the  determination 
of  potash  a  standard  solution  of  oxalic  acid  is  always  used. 

Ammonium  carbonate  is  used  for  decomposing  metallic 
sulphates  which  are  formed  during  the  roasting  process  of 
several  sulphur  minerals.  Ammonium  sulphate  is  then 
formed,  which  is  volatile  when  slightly  heated. 

7.  NITRE,  SALTPETRE,  OR  POTASSIUM  NITRATE  has  a  very 
powerful  action  on  the  sulphides  :  in  fact,  if  not  modified 
by  the  addition  of  some  inert  substance,  as  an  alkaline 
carbonate  or  sulphate,  explosion  may  take  place,  and  a 
portion  of  the  contents  of  the  crucible  be  thrown  out. 
Where  an  excess  of  nitre  is  used,  all  the  sulphur  is  con- 
verted into  sulphuric  acid,  and  every  metal  but  gold  and 
silver  is  oxidised.     When  only  the  exact  quantity  of  nitre 
is  employed,  that  is  to  say,  just  as  much  as  is  sufficient 
to  burn  all  the  sulphur  in  the  sulphides  of  those  metals 
which  are  not  very  oxidisable,  as  those  of  copper,  silver, 
and  lead,  the  metal  is  obtained  in  a  state  of  purity,  and 
the  whole  of  the  sulphur  converted  into  sulphuric  acid  ; 
but  with  the  sulphides  of  the  very  oxidisable  metals,  the 
•oxygen  of  the  nitre  is  divided  between  the  sulphur  and 
the  metal. 

8.  LEAD  NITRATE  possesses  the  combined  properties  of 
nitre  and  litharge.     It  is  not  much  used. 

9.  LEAD  SULPHATE  is  not  used  as  a  reagent,  but  is  often 
formed  in  the  assay  of  lead  ores.     It  decomposes  lead 
sulphide   by  burning   the  sulphur   (PbO,S03  +  PbS  =  2Pb 
+  2S02).     It  acts  on  many  other  sulphides  in  a  similar 
manner. 

IV.    SULPHURISING   REAGENTS. 

1.  Sulphur. 

2.  Cinnabar,  or  mercury  sulphide. 
o.  Galena. 

4.  Antimony  sulphide. 

5.  Iron  pyrites. 

6.  The  alkaline  persulphides 


SULPHURISING    REAGEXTS.  189 

1.  SULPHUR  fuses  at  226°,  and  at  284°  is  very  liquid. 
It  has  very  powerful  affinities,  and    combines  with  the 
greater  number  of  the  metals.    That  kind  generally  known 
as  flowers  of  .sulphur  ought  to  be  employed;   and  before 
use,  the  presence  or  absence  of  earthy  matters  should  be 
ascertained,  by  exposing  it  to  a  dull  red-heat  in  a  crucible. 
The  sulphur  will  go  off,  and  the  earthy  impurities  will  be 
left  behind. 

Sulphur  is  principally  used  in  the  preparation  of  the 
alkaline  sulphides  and  in  the  assay  of  some  of  the  noble 
metals. 

2.  CINNABAR  is  decomposed  by  many  of  the  metals,  and 
is  a  better  sulphurising  agent  than  sulphur  itself,  as  it  is 
less  volatile. 

3.  GALENA. — Many  metals,  as  iron,  copper,  &c.,  separate 
sulphur  from  lead,  while  some  others,  as  silver,  gold,  &c., 
do  not ;  so  that  if  galena  be  heated  with  an  alloy  of  various 
metals,  some  of  which  decompose  it.  and  some  do  not,  the 
former  are  transformed  into  sulphides,  and  the  latter  com- 
bine with  the  metallic  lead  which  is  produced.    It  is  often 
employed  for  this  purpose.    It  is  a  common  ore,  and  readily 
procured. 

The  samples  employed  must  contain  no  antimony  sul- 
phide, and  all  the  matrix  must  be  carefully  separated  by 
sifting  and  washing. 

4.  ANTIMONY  SULPHIDE  yields  its  sulphur  to   many  of 
the  metals,  but  it  is  only  used  in  the  separation  of  gold 
from  some  alloys.      In  this  operation  the  sulphur  com- 
bines with  the  alloyed  metals,  and  the  antimony  with  the 
gold,  for  which  it  has  much  affinity. 

5.  IRON  PYRITES  is  a  persulphide  which  loses  half  its 
sulphur  at  a  white  heat.     It  is  much  employed  in  metal- 
lurgical operations,  but  not  in  assaying. 

6.  ALKALINE    PERSULPHIDES   can    support   a   tolerably 
elevated  temperature  without  losing   sulphur,  but  they 
have  a  great  tendency  to  do  so,  and  to  this  is  due  their 
sulphurising  power.     By  their  means  almost  every  metal 
can  be  made  to  combine  with  sulphur.     When  an  alkaline 
persulphide  is  heated  with  a  metal,  or  an  oxide  of  a  metal 


190  FLUXES. 

mixed  with  charcoal,  a  fused  compound,  a  mixture  of  the 
sulphide  of  the  metal  and  an  alkaline  sulphide,  is  obtained. 

When  they  are  in  combination,  they  are  held  together 
by  very  feeble  affinities,  and  their  decomposition  is  gener- 
ally effected  by  the  mere  action  of  water,  which  dissolves 
the  alkaline  sulphide  and  leaves  the  other  perfectly  pure. 
But  with  gold,  molybdenum,  tungsten,  antimony,  &c.,  the 
compound  is  stable  and  soluble  in  water  ;  and  it  is  from 
this  fact  that  the  alkaline  sulphides  are  sometimes  employed 
in  the  assay  of  auriferous  substances, 

In  order  to  effect  a  sulphurisation  by  means  of  the 
alkaline  sulphides,  it  is  much  better  to  use  equivalent 
mixtures  of  sulphur  and  alkaline  carbonates  than  to  pre 
pare  them  beforehand.  To  obtain  potassium  persulphide, 
46  parts  of  potassium  carbonate,  and  54  of  flowers  of 
sulphur,  must  be  fused  together  ;  and  for  sodium  per- 
sulphide, 40  parts  of  dry  sodium  carbonate  must  be  heated 
with  60  parts  of  sulphur. 

When  the  mixture  is  fused  in  a  plain  crucible,  potas- 
sium sulphate,  or  sodium  sulphate  is  formed,  because  part 
of  the  alkali  gives  up  its  oxygen  to  a  portion  of  the 
sulphur,  which  becomes  sulphuric  acid  ;  but  when  char- 
coal-lined crucibles  are  used,  the  carbon  combines  with 
the  oxygen  of  the  alkali,  and  no  sulphate  is  produced. 


v.  FLUXES. 

Fluxes  are  used  in  the  following  cases : — 

1st.  To  cause  the  fusion  of  a  body,  either  difficultly 
fusible,  or  infusible  by  itself. 

2ndly.  To  fuse  foreign  substances  mixed  with  a  metal, 
in  order  to  allow  the  latter  to  separate  by  its  difference  of 
specific  gravity. 

3rdly.  To  destroy  a  compound  into  which  an  oxide 
enters,  and  which  prevents  the  oxide  being  reduced  by 
charcoal.  Zinc  silicate,  for  instance,  yields  no  metallic 
zinc  with  charcoal,  unless  it  be  mixed  with  a  flux  capable 
of  combining  with  the  silica. 

4thly.    To  prevent  the  formation  of  alloys   of  some 


NON-METALLIC   FLUXES.  191 

metals  with  others,  as,  for  ^  instance,  in  the  case  of  a  mix- 
ture of  the  manganese  and  iron  oxides  ;  when  a  suitable 
iiux  is  employed,  the  iron  is  obtained  in  a  state  of  purity, 
whereas  if  no  flux  had  been  added  an  alloy  would  have 
been  obtained.  Gold  and  silver  can  be  separated  from 
many  other  metals  by  means  of  a  flux. 

5thly.  To  scorify  some  of  the  metals  contained  in  the 
substance  to  be  assayed,  and  obtain  the  others  alloyed 
with  a  metal  contained  in  the  flux,  as  gold  or  silver  with 
lead. 

6thly.  A  flux  may  be  employed  to  obtain  a  single 
button  of  metal,  which  otherwise  would  be  obtained  in 
globules. 

Fluxes  are  divided  into  non-metallic  and  metallic  ;  the 
non-metallic  fluxes  are — 

1.  Silica. 

2.  Lime. 

3.  Magnesia. 

4.  Alumina. 

o.  Calcium  and  aluminium  silicates. 

6.  Glass. 

7.  Borax  (sodium  biborate). 

8.  Fluor-spar  (calcium  fluoride). 

9.  Potassium  carbonate. 

10.  Sodium  carbonate. 

11.  Nitre  (potassium  nitrate). 

12.  Common  salt  (sodium  chloride). 

13.  Black  flux  and  its  equivalents. 

1 4.  Argol  (potassium  bitartrate). 

15.  Salt  of  sorrel  (potassium  binoxalate). 

16.  Soap. 

The  metallic  fluxes  are — 

17.  Litharge  (lead  oxide)  and  ceruse  (lead  carbonate). 

18.  Glass  of  lead  (lead  silicate). 

19.  Lead  borate, 

20.  Lead  sulphate. 

21.  Copper  oxide. 

22.  Iron  oxides. 


192  SILICA,    LIME,    BORAX. 

1.  SILICA  is  employed  frequently  to  cause  the  fusion  of 
some  gangues  in  assays  made  at  an  elevated  temperature. 
Silica  combines  with  all  the  bases,  and  forms  with  them 
bodies  termed  silicates,  which  are  more  or  less  fusible. 

Quartz  is  the  best  form  of  silica  to  use.  For  that  pur- 
pose it  must  be  strongly  heated,  and  then  quenched  in  cold 
water.  It  can  then  be  easily  pulverised.  In  case  the 
quartz  takes  a  yellow  or  reddish  colour  on  ignition,  it 
must  be  digested  with  hydrochloric  acid. 

2,  3,  4,  5.  LIME,  MAGNESIA,  ALUMINA,  AND  THEIR  SILICATES. 
No  simple  silicate  is  readily  fusible,  so  that  lime,  magnesia,, 
or    alumina   are   employed,   according  to  circumstances, 
to  reduce  a  simple  silicate  to  such  a  condition  that  it  will 
readily  fuse  in  an  assay  furnace.     Sometimes  it  may  be  re- 
quisite to  use  all  the  above-mentioned  earths. 

Pure  lime,  when  exposed  to  atmospheric  air,  attracts 
carbonic  acid  and  water  so  quickly  that,  in  practice,  pure 
calcium  carbonate  is  used  in  the  form  of  chalk,  calcareous 
spar,  or  marble,  if  they  are  pure.  Calcium  carbonate  fre- 
quently contains  foreign  substances,  viz.  iron,  manganese, 
alumina,  silica,  and  also  magnesium  carbonate.  A  certain 
quantity  of  magnesium  carbonate  is,  in  many  cases,  advan- 
tageous, and  alumina  and  silica  are  not  disadvantageous. 

Alumina  is  never  used  in  the  pure  state.  Washed 
china-clay  which,  on  burning,  becomes  white,  is  used 
instead.  Clay  generally  contains  from  20  to  about  40  per 
cent,  alumina,  and,  if  it  is  used  for  the  formation  of  sili- 
cates, a  quantitative  analysis  of  its  components  should 
first  be  performed. 

6.  GLASS  is  a  very  useful  flux  in  certain  assays,  and, 
being  a  saturated  silicate,  it  will  serve  by  itself  either  as  a 
slag  or  merely  as  a  covering.     The  kind  employed  must 
contain  no  easily  reducible  metallic  oxides,  and  it  must 
especially  be  free  from  arsenious  acid  and  lead  oxide. 

The  subjoined  analyses  of  glass  from  Bodemann  KerVs 
Probierkunst  will  be  found  useful.  (See  p.  193.) 

7.  BORAX   (Na2B407  +  10H20    and    Na2B407  +  5H20). 
— That  kind   with    10    atoms    or    47'1    per   cent,   water 
effloresces  when  exposed  to  atmospheric  air,  and  the  other 


ANALYSES   OF    GLASS. 


193 


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194  FLUXES — FLUOR   SPAR,  ALKALINE    CARBONATES. 

kind  with  5  atoms  or  30  per  cent,  water,  does  not  efflor- 
esce, and  crystallises  in  octahedrons.  This  difference  is 
immaterial  for  assaying  purposes,  but  it  is  of  importance 
in  purchasing  borax. 

When  borax  is  heated,  it  loses  its  water  of  crystalli- 
sation and  undergoes  an  enormous  increase  of  volume  ;  at 
a  higher  temperature,  it  fuses  and  forms  a  transparent 
glass,  which  becomes  dull  on  the  surface  by  exposure  to 
air.  Only  the  fused  vitrified  borax  ought  to  be  used  in 
assays.  It  must  be  reduced  to  powder,  and  kept  in  well- 
closed  vessels. 

Borax  may  be  regarded  as  containing  free  boracic 
acid ;  it  is  an  excellent  and  nearly  universal  flux :  it  has 
the  property  of  forming,  like  boracic  acid,  fusible  com- 
pounds with  silica  and  nearly  all  the  bases,  and  is  prefer- 
able to  boracic  acid  because  it  is  much  less  volatile.  It  may 
be  used  at  a  high  or  a  low  temperature.  It  is  employed 
in  the  assay  of  gold  and  silver,  because  it  fuses  and  coin- 
bines  with  most  metallic  oxides,  or  in  obtaining  a  regulus 
— that  is  to  say,  to  separate  the  metals,  their  arsenides  and 
sulphides,  from  any  stony  matter  with  which  they  may  be 
mixed ;  because  this  salt  is  neither  oxidising  nor  desul- 
phurising. It  is  also  employed  in  the  assay  of  iron  and 
tin  ores,  as  in  the  presence  of  charcoal  it  retains  but  traces 
of  their  oxides,  and,  indeed,  much  less  than  generally  re- 
mains with  the  silicates. 

8,  FLUOR-SPAR  or  CALCIUM  FLUORIDE  is  rarely  employed 
in  assays,  but  in  certain  cases  is  an  excellent  flux ;  as  will 
be  hereafter  shown. 

9,  10.  POTASSIUM  CARBONATE  and  SODIUM  CARBONATE. — It 
has  been  already  shown  that  they  possess  oxidising  and 
desulphurising  power:    they  will  now  be  considered    as 
fluxes. 

They  are  decomposed  in  the  dry  way  by  silica  and  the 
silicates,  with  the  separation  of  carbonic  acid.  The  presence 
of  charcoal  much  facilitates  this  decomposition. 

They  form  fusible  compounds  with  many  metallic 
oxides.  In  these  combinations  the  oxide  replaces  a  cer- 
tain quantity  of  carbonic  acid  ;  but  they  are  not  stable — 


FLUXES — ISTITRE,   COMMON   SALT.  195 

they  are  decomposed  by  carbon,  which  reduces  the  oxides, 
or  by  water,  which  dissolves  the  alkali. 

On  account  of  their  great  fusibility,  the  alkaline  car- 
bonates can  retain  in  suspension,  without  losing  their 
iiuidity,  a  large  proportion  of  pulverised  infusible  sub- 
stances, as  an  earth,  charcoal,  &c. 

The  alkaline  carbonates  ought  to  be  deprived  of  their 
water  of  crystallisation,  for  assaying  purposes  ;  in  fact,  it 
would  be  better  to  fuse  them  before  use.  They  must  in 
all  cases  be  kept  in  well-stopped  vessels. 

They  may  be  used  indifferently,  but  sodium  carbonate 
is  to  be  preferred,  as  it  does  not  deliquesce,  and  is  gener- 
ally much  cheaper. 

The  alkaline  carbonates  of  commerce  always  contain 
sulphates  and  chlorides.  In  some  cases  this  causes  no  in- 
convenience, but  there  are  many  circumstances  in  which 
the  presence  of  sulphuric  acid  would  be  injurious. 

Potassium  carbonate  can  readily  be  procured  free  from 
sulphate  and  chloride  by  means  of  nitre  and  charcoal,  as 
follows:  Pulverise,  roughly,  6  parts  of  pure  nitre,  and 
mix  them  with  1  part  of  charcoal ;  then  project  the 
mixture,  spoonful  by  spoonful,  into  a  red-hot  iron  crucible. 
The  projection  of  each  spoonful  is  accompanied  by  a  vivid 
deflagration,  and  potassium  carbonate  is  found  in  a  fused 
state  at  the  bottom  of  the  crucible.  It  must  be  pulve- 
rised, separated  from  excess  of  charcoal,  and  kept  in  a  dry 
state  for  use. 

Sodium  carbonate  may  be  obtained  in  much  the  same 
way,  substituting  sodium  nitrate  for  potassium  nitrate. 
Either  carbonate  may  also  be  obtained  in  a  sufficient  state 
of  purity  by  repeatedly  crystallising  the  commercial  car- 
bonates. 

11.  POTASSIUM  NITRATE. — Its   properties  have  already 
been  pointed  out.     The  presence  of  silica  or  of  silicates 
much  assists  its  decomposition. 

12.  COMMON  SALT  (SODIUM  CHLORIDE)    is  recommended 
either  mixed  with  flux,  or  placed  above  it,  for  the  purpose 
of  preserving  the  substance  beneath  from  the  action  of 
the  atmosphere,  or  to  moderate  the  action  of  such  bodies 

o  2 


196  WHITE,   BLACK,   AXD    RAW   FLUX. 

as  cause  much  ebullition.  It  is  very  useful  in  lead  assays,, 
and  is  much  used  in  the  assay  of  silver  by  the  wet  way. 
It  must  be  previously  pounded,  and  heated  to  dull  redness 
in  a  crucible,  to  prevent  its  decrepitation. 

Common  salt,  though  containing  calcium  and  magne- 
sium sulphates  and  chlorides,  is  in  most  cases  sufficiently 
pure  for  assaying  purposes.  If  intended  for  copper  assays, 
it  must  be  previously  purified  from  sulphates. 

Plattner  *  has  examined  the  influence  of  common  salt 
upon  different  oxides  and  sulphates.  It  does  not  act  upon 
uncombined  lead  and  zinc  oxides.  Lead  sulphate,  when 
melted  with  it  at  a  dull  red  heat,  becomes  liquid,  and 
evolves  vapour  of  lead  chloride.  By  raising  the  tempera- 
ture, and  by  giving  more  draught  of  air,  the  evolution  of 
such  vapour  is  increased.  Common  salt  acts  upon  zinc 
sulphate  in  the  same  way.  Antimony  oxide  and  antimo- 
nious  acid  heated  with  it  at  a  dull  red  heat  evolve  vapour 
of  antimony  chloride,  though  not  in  a  great  quantity. 
Copper  sulphate  melted  with  salt  at  a  red  heat  becomes- 
converted  into  copper  chloride  and  sodium  sulphate.  Cop- 
per chloride  becomes  vaporised  if  air  is  admitted,  and  it 
becomes  converted  into  copper  subchloride  by  raising  the 
temperature  a  little,  chlorine  being  then  evolved. 

13.  WHITE  FLUX,  BLACK  FLUX,  and  RAW  FLUX. —  White  flux 
is  produced  by  deflagrating  together  equal  parts  of  salt- 
petre and  argol  (crude  potassium  bitartrate) ;  black  flux •, 
by  deflagrating  one  part  of  saltpetre  with  two  or  three  or 
more  parts  of  argol.  Generally  one  part  of  saltpetre  and 
two  and  a  half  parts  of  argol  are  taken.  The  finely  pul- 
verised and  intimate  mixture  for  either  flux,  before  it  is 
deflagrated,  is  called  raw  flux. 

After  the  saltpetre  and  argol  have  been  finely  pulver- 
ised and  sifted  separately,  they  are  intimately  rubbed  to- 
gether, and  then  deflagrated  by  throwing  the  mixture  little 
by  little  into  a  low- red-hot  crucible,  which  after  each 
addition  is  lightly  covered  over.  The  deflagration  may 
also  be  conducted,  though  less  advantageously,  by  filling 
the  crucible  about  two-thirds  full  of  the  raw  flux  and  then 

*  '  B.  u.  h.  Ztg-.'  1854,  p.  126. 


WHITE,   BLACK,   AND    RAW   FLUX.  197 

touching  it  with  a  red-hot  coal  or  iron.  It  can  only  be 
performed  in  the  open  air  or  under  a  flue  with  a  strong 
draft,  as  the  tartaric  acid  evolves  various  empyreumatic 
volatile  matters  in  considerable  quantity  during  its  decom- 
position. 

With  white  flux  the  saltpetre  suffices  to  burn  all  the 
charcoal  produced  by  the  carbonisation  of  the  tartaric 
acid,  and  the  result  is  therefore  almost  pure  potassium 
carbonate,  if  pure  saltpetre  and  pure  argol  have  been  used. 
If  the  latter  were  impure,  the  resulting  neutral  potassium 
carbonate  may  contain  much,  perhaps  10  per  cent.,  of  cal- 
cium carbonate.  White  flux  works  like  ordinary  potas- 
sium carbonate,  which  is  therefore  almost  always  preferred 
to  the  far  more  expensive  flux. 

With  the  black  flux  the  quantity  of  saltpetre  is  not 
sufficient  to  burn  all  the  carbon  from  the  argol,  and  there 
remain  therefore  in  the  black  flux,  according  as  two,  two 
and  a  half,  or  three  parts  of  argol  were  taken,  about  5, 
8,  or  12  per  cent,  of  free  carbon,  which  is  mixed  in  the 
most  intimate  manner  with  the  resulting  neutral  potassium 
carbonate — more  intimately  indeed  than  would  be  possible 
by  any  mechanical  means.  This  charcoal  does  not  hinder 
the  fusing  of  the  assay  when  the  flux  is  used,  and  effects  or 
promotes  the  reduction  of  the  metallic  oxides. 

Fusion  and  reduction,  sometimes  also  desulphurisation, 
are  the  purposes  for  which  black  flux  is  used,  and,  accord- 
ing to  the  special  character  of  the  assay,  a  greater  or  a  less 
proportion  of  charcoal  to  the  carbonate  of  potash  may  be 
desirable,  and  this  is  to  determine  whether  two,  two  and 
a  half,  three,  or  more  parts  of  argol  are  to  be  used,  to  one 
of  saltpetre.  As  a  general  rule  it  may  be  stated,  the  more 
difficultly  fusible  is  the  assay,  the  more  potash  ;  and  the 
more  metallic  oxide  is  to  be  reduced,  the  more  charcoal ; 
and  the  more  also  of  the  latter,  the  more  oxygen  the  oxide 
contains. 

In  many  cases,  instead  of  black  flux,  a  mixture  of  po- 
tassium carbonate  and  powdered  charcoal,  in  a  suitable 
ratio  to  each  other,  suffices,  especially  if  the  mixture,  before 
use,  is  passed  through  a  sieve,  or  otherwise  very  intimately 


198  FLUXES — CREAM  OF  TARTAR. 

mingled.  Instead  of  the  powdered  charcoal,  also,  a  corre- 
sponding (about  twice  or  four  times  as  large)  quantity  of 
flour,  sugar,  or  starch  may  be  mixed  with  the  potassium 
carbonate.  Lampblack  is,  however,  the  best  form  of  car- 
bon. The  three  following  fluxes  are  very  useful : — 

Sodium  carbonate    «       '  ,         .         .         .94        88        816 
Charcoal  .        .'.;,.        .        .     6        12        184 

The  second  is  very  nearly  equivalent  to  sodium  and 
carbonic  acid,  and  the  third  to  sodium  and  carbonic  oxide  ; 
but  it  must  be  observed  that,  whatever  precautions  be 
taken,  these  mixtures  never  become  so  liquid  as  black 
flux,  because  the  charcoal  tends  very  much  to  separate  and 
rise  to  the  surface. 

A  mixture  of  100  parts  of  pure  potassium  carbonate 
and  10  to  15  parts  of  wheat  or  rye  flour  is  to  be  preferred 
to  black  flux  in  case  the  argol  contains  gypsum,  or  the 
saltpetre,  sulphates,  which  in  many  cases  might  work  in- 
juriously upon  the  assay.  If  this  is  the  case,  then,  in  the 
presence  of  a  reducing  flux,  sodium  sulphide  is  apt  to  form, 
which,  for  example  in  the  copper  assay,  occasions  the 
slagging  of  copper. 

Cream  of  tartar,  carbonised  by  a  semi-combustion  until 
it  is  reduced  to  half  its  weight,  is  a  very  good  substitute 
for  black  flux ;  it  contains  about  10  per  cent,  of  charcoal. 

As  a  perfectly  general  rule  for  the  use  of  black  flux, 
and  of  mixtures  similar  to  it,  it  is  to  be  observed  that  the 
crucible  should  never  be  more  than  two-thirds  filled,  as 
the  assay  always  intumesces,  i.e.  evolves  gaseous  matters, 
when  free  carbon  is  present. 

14.  ARGOL,  CREAM  OP  TARTAR,  or  POTASSIUM  BITARTRATE. — 
When  potassium  bitartrate  is  heated  in  a  covered  crucible, 
a  rapid  decomposition  takes  place,  accompanied  by  a  dis- 
engagement of  inflammable  gases  :  the  substance  agglo- 
merates, but  without  fusing  or  boiling  up.  The  residue 
is  black  and  friable,  and  contains  15  per  cent,  of  carbon 
when  produced  from  rough  tartar  or  argol,  and  7  per 
cent,  from  cream  of  tartar. 

These  reagents  produce  the  same  effects  as  black  flux, 
and  possess  more  reducing  power,  because  they  contain 


FLUXES — SOAP.  199 

more  combustible  matter  :  but  this  is  an  inconvenience, 
for  the  excess  prevents  their  entering  into  full  fusion  when 
the  substance  to  be  assayed  requires  but  a  small  propor- 
tion of  a  reducing  agent.  They  can  be  used  with  success 
in  assays  requiring  much  carbonaceous  matter. 

15.  SALT   OF  SORREL,   or   POTASSIUM   BINOXALATE,  when 
heated,  is  decomposed.     It  decrepitates  feebly,  and  during 
its  decomposition  is  covered  with  a  blue  flame  ;  it  at  first 
softens,  and  when  fully  fused  is  wholly  converted  into  car- 
bonate. When  the  oxalate  is  very  pure,  the  resulting  car- 
bonate is  perfectly  white,  and  free    from  charcoal :  but 
very  often  it  is  spotted  with  blackish  marks.     It  has  no 
very  great  reducing  power. 

16.  WHITE  or  MOTTLED  SOAP  is  a  compound    of  soda 
with  a  fatty  acid.     When  heated  in  closed  vessels  it  fuses, 
boiling   up  considerably,    and   during   its   decomposition 
gives  off  smoke  and  combustible  gases,  and  leaves  a  residue 
composed  of  sodium  carbonate  with  about  5  per  cent,  of 
charcoal.     Of  all  reducing  agents,  soap  absorbs  the  great- 
est quantity  of  oxygen  ;  and  as  the  residue  of  its  decom- 
position  by   heat  affords  but  little  charcoal,  it  has  the 
property  of  forming  very  fluid  slags.     Nevertheless,  it  is 
rarely  employed,  because  Certain  inconveniences  outweigh 
its  advantages.    These  inconveniences  are,  its  bubbling  up, 
and  its  extreme  lightness.     It  also  requires  to  be  rasped,  in 
order  to  mix  it  perfectly  with  the  substances  it  is  to  decom- 
pose, and  it  then  occupies  a  very  large  volume,  and  requires 
correspondingly  large  crucibles.     By  mixing  rasped  soap 
with  potassium  binoxalate  or  sodium  carbonate  excellent 
reducing  fluxes  may  be  made. 

Reducing  Power  of  the  various  Fluxes. — By  fusing 
equal  weights  of  each  of  the  above-mentioned  reducing 
fluxes  with  an  excess  of  litharge,  the  following  quantities 
of  lead  were  yielded  : — 

Common  black  flux,  made  with  two  parts  of  tartar     .  .  T40 

Ditto,  with  2f  of  tartar  .....  1'90 

Ditto,  with  3  of  tartar  .  .  .  .  .  3'80 

Sodium  carbonate          .     94  J  -,  .an 

f*n  i  .-»>....  J.  OU 

Charcoal  .  6  j 

Sodium  carbonate          .88  Q.«A 

Charcoal  .  .     12  j 


200 


METALLIC   FLUXES. 


Sodium  carbonate  90 

Sugar    .            .  10 

Sodium  carbonate  80 

Sugar    .             .  20 

Sodium  carbonate  90 

Starch  .            .-  10  f 

Sodium  carbonate  80 

Starch  .            ."  20 

Crude  tartar,  argol  .  - 

Cream  of  tartar  : 

Salt  of  sorrel     .  85 

Soap     „'.       .,  .    '  15 

Sodium  carbonate  85 

Soap      .            ;'•  15 
Cream  of  tartar,  carbo  ised 
Ditto,  ditto,  calcined 
Potassium  binoxalate 
White  soda  soap      .:  *  ', 


1-40 
2-80 
1-15 

2-30 

5-60 
4-50 

3-35 

2-40 

3-10 

2-20 

•90 

16-00 


All  fluxes  containing  alkaline  and  carbonaceous  sub- 
stances are  reducing  and  desulphurising,  besides  acting  as 
fluxes,  properly  so  called.  They  also  produce  another 
effect  which  it  is  useful  to  know,  viz.  they  have  the  pro- 
perty of  introducing  a  certain  quantity  of  potassium  or 
sodium  into  the  reduced  metal.  This  was  first  pointed  out 
by  M.  Vauquelin.*  He  found  that  when  antimony,  bis- 
muth, or  lead  oxide  was  fused  with  an  excess  of  tartar,  the 
metals  obtained  possessed  some  peculiar  characters,  which 
they  owed  to  the  presence  of  potassium. 


METALLIC  FLUXES. 


17.  LITHARGE  AND  CERUSE. — These  bodies  always  act  as 
fluxes,  but  at  the  same  time  often  produce  an  alloy  with 
the  metal  contained  in  the  ore  to  be  assayed.  Ceruse 
produces  the  same  fluxing  effect  as  litharge.  The  former 
is  the  better  flux,  and  is  very  useful  in  a  great  number  of 


18.  GLASS  OF  LEAD  (LEAD  SILICATE). — Lead  silicates  are 
preferable  to  litharge  in  the  treatment  of  substances  con- 
taining no  silica,  or  which  contain  earths  or  oxides  not 
capable  of  forming  a  compound  with  lead  oxide,  excepting 
by  the  aid  of  silica.  It  may  be  made  by  fusing  1  part  of 
sand  with  four  parts  of  litharge :  if  required  more  fusible, 
a  larger  proportion  of  litharge  must  be  added. 

*  l  Annales  des  Mines.' 


METALLIC   FLUXES.  201 

19.  LEAD  BORATE. — The  lead  borates  are  better  fluxes 
than  the  silicates  when  the  substance  to  be  assayed  con- 
tains free  earths  ;  but  in  order  to  prevent  them  swelling 
up  much  when  fused,  they  must  contain  an  excess  of  lead 
oxide.     The  lead  borate  containing  90'56  of  lead  oxide 
and  9 '44  of  boracic  acid,  is  very  good.     Instead  of  lead 
borate,  a  mixture  of  fused   borax  and  litharge  may  be 
employed  ;  it  is  equally  serviceable. 

20.  LEAD   SULPHATE   is   decomposed   by   all    siliceous 
matters,  and  by  lime,  so  that  when  these  substances  are 
present  litharge  is  produced,  which  fluxes  them. 

21.  COPPER  OXIDE  is  rarely  used  as  a  flux  for  oxidised 
matters,  but  is  sometimes  employed  in  the  assays  of  gold 
and  silver,  to  form  an  alloy  with  those  metals.    In  this  case 
a  reducing  flux  must  be  mixed  with  the  oxide.     Metallic 
copper  may  be  used,  but  is  not  so  useful,  as  it  cannot  be 
so  intimately  mixed  with  the  assay. 

22.  THE  IRON  OXIDES  are  good  fluxes  for  silica  and  the 
silicates.     They  are,  however,  rarely  employed  for  that 
purpose  ;  they  are  more  often  used  to  introduce  metallic 
iron  into  an  alloy  to  collect  an  infusible,  or  nearly  infusible, 
metal,   by   alloying   it   with   iron ;   such    as   manganese, 
tungsten,  or  molybdenum. 


202 


CHAPTER  VII. 

THE   BLOWPIPE   AND    ITS   USE. 

THE  BLOWPIPE  was  formerly  only  used  by  jewellers  and 
workers  of  metal  for  producing  sufficient  heat  for  soldering 
certain  small  portions  of  their  work  ;  and  it  was  not  till 
about  the  year  1733  that  Anton  Swab  applied  it  to  the 
analysis  of  mineral  substances.  Cronstedt  used  the  blow- 
pipe to  ascertain  the  difference  between  various  mineral 
substances  as  to  fusibility,  &c.  In  1765  Von  Engestrom 
published  Cronstedt's  System  of  Mineralogy,  and  added  to 
it  a  Treatise  on  the  Blowpipe,  in  which  he  pointed  out  the 
processes  of  Cronstedt. 

This  work  attracted  the  attention  of  philosophers  to  this 
valuable  instrument,  and  its  use  became  more  general,, 
and  was  further  developed  by  Bergman  and  Gahn. 

Berzelius,  after  Gahn,  was  particularly  famed  for  his 
skill  with  the  blowpipe,  and  for  his  improvements  in  the 
form  of  apparatus  ;  and  from  his  excellent  work  on  this 
subject  some  of  the  following  descriptive  part  of  Blowpipes, 
Lamps,  Tongs,  &c.,  is  derived. 

The  common  blowpipe  of  gasfitters,  jewellers,  &c.,  is  a 
tube  of  brass,  tapering  towards  one  end,  and  curved  at 
that  extremity,  which  has  an  opening  as  fine  as  that  made 
by  the  finest  needle  ;  it  is  this  opening  which  is  held 
against  the  flame  of  the  lamp,  and  air  is  blown  to  it  to 
increase  the  amount  of  heat.  In  all  ordinary  operations, 
the  blast  is  required  to  be  kept  up  not  more  than  a  minute,, 
so  that  the  quantity  of  moisture  exhaled  from  the  lungs 
produces  no  inconvenience  by  stopping  up  the  tube.  But 
in  certain  chemical  operations,  this  is  exceedingly  trouble- 
some, as  a  continuous  blast  is  required,  and  a  large 


THE    BLOWPIPE    AND    ITS   USE. 


203 


68. 


quantity  of  water  collects  in  consequence,  generally 
sufficient  to  mar  the  success  of  an  experiment.  In  order 
to  obviate  this,  Cronstedt  placed  in  the  centre  of  his 
blowpipe  a  bulb,  in  which  the  greater  part  of  the  water 
collected.  This  form  was,  however,  inconvenient,  because 
if  the  jet  of  the  blowpipe  were  at  all  inclined,  even  for  an 
instant,  the  water  ran  from  the  bulb  and  filled  it.  In  a 
series  of  articles  communicated  to  the  '  Chemical  News,' 
Mr.  David  Forbes,  F.R.S.,  has  given  directions  which  are 
invaluable  to  all  who  practise  with  this  instrument. 
From  these  w^e  quote  the  following. 

'  BLOWPIPE. — The  form  adopted  long  ago  by  Gahn  is  con- 
sidered as  the  most  convenient. 
Fig.  68  shows  an  improvement 
made  by  the  author  upon  this 
form. 

'In  this  figure  it  will  be  seen 
that  the  arm  of  the  jet  is 
double,  turning  upon  a  central 
hollow  axis,  which  allows  the 
blast  to  be  directed  at  will 
through  either  half  of  the  arm, 
merely  by  rotating  the  arm  it- 
self half  round ;  by  having  con- 
sequently the  two  holes  with 
respectively  a  large  and  small 
orifice,  a  corresponding  blast 
may  be  obtained  at  pleasure, 
without  suspending  the  opera- 
tion. 

'  As  a  more  steady  and 
long-continued  blast  is  required 
in  quantitative  operations  than 
could  be  kept  up  by  using  a 
blowpipe  provided  with  an 
ordinary  mouthpiece  held  be- 
tween the  lips  without  seriously 
distressing  the  muscles  of  the 
cheeks,  it  is  quite  essential  that  the  trumpet  mouthpiece 


201  MR.    FORBES  S   BLOWPIPE. 

shown  in  fig.  68  be  adopted  ;  for  the  same  reasons  also 
the  mode  of  holding  the  blowpipe  represented  in  fig.  69  is 
recommended,  as  securing  the  great- 
est steadiness  from  motion,  and  as 
greatly  assisting  the  muscles  of  the 
cheeks  by  the  external  support  af- 
forded them  by  the  position  of  the 
thumb  pressing  against  the  trumpet 
mouthpiece. 

'  The  nipples  are  turned,  and  bored 
of  three  different  sizes,  and  are  made  both  of  platinum 
and  of  brass.  The  first,  of  platinum,  contains  the  smallest 
aperture,  and  is  employed  for  qualitative  analysis ;  the 
second,  of  brass,  is  used  for  such  qualitative  experiments 
as  require  a  strong  oxidising  flame,  and  for  heating  silver, 
gold,  and  copper,  in  quantitative  assay  ;  also  for  roasting 
copper,  lead,  and  tin  ores,  the  metallic  contents  of  which 
are  to  be  accurately  determined  ;  and  the  third,  which  is 
also  manufactured  of  brass,  has  the  largest  bore,  and  is 
used  for  the  quantitative  estimation  of  lead  and  tin. 

'  Platinum  nipples  are,  however,  always  preferable  to 
those  of  brass,  because  by  exposure  to  a  moderate  red 
heat  on  charcoal  before  the  blowpipe,  they  are  more  easily 
•cleaned  from  the  sooty  particles  which  obstruct  the 
aperture.  This  method  of  cleansing  cannot  be  applied  to 
brass  nipples,  owing  to  their  rapid  oxidisation  ;  to  clean 
these  the  operator  must  adapt  in  the  opening  a  sharp- 
pointed  fragment  of  horn,  or  a  small  needle,  ground  along 
one  half  of  its  length  ;  by  this  means  the  aperture  through 
which  the  air  passes  may  be  readily  cleansed.' 

The  power  and  perfection  of  the  blowpipe  flame  greatly 
depends  upon  the  internal  construction  of  these  jets  or 
nipples.  The  current  of  air  for  at  least  three-quarters  of 
an  inch  of  the  orifice  should  meet  with  no  obstruction  or 
roughness  such  as  a  screw  thread  or  angle  so  frequently 
met  with  in  blowpipes  having  removable  nozzles.  The 
most  perfect  form  for  the  blowpipe  jet  is  that  obtained  by 
slightly  thickening  and  drawing  down  a  piece  of  glass 
tubing  of  about  5  millims.  internal  diameter  to  the  required 


BLOWPIPE   JETS.  205 

size  for  the  jet,  then  cutting  the  contracted  part  cleanly 
across  at  a  point  about  half  an  inch  from  one  of  tjie 
shoulders.  We  then  have  a  jet  of  the  shape  shown  in 


FIG.  TO. 


fig.  70,  with  which  the  most  beautiful  flame  can  be  pro- 
duced, and  almost  any  desired  pressure  of  air  used  without 
hissing. 

It  is  needless,  however,  to  remark  that  the  liability  of 
glass  jets  to  crack  and  fuse  render  their  use  impracticable 
except  for  an  oxidising  flame,  where  the  jet  need  not  be 
inserted  in  the  flame  of  the  lamp.  Metal  therefore  must 
be  resorted  to,  and,  as  the  superiority  of  the  glass  jets 
solely  depends  on  their  internal  shape  and  smoothness,  the 
nearer  the  metal  jets  can  be  made  to  approach  them  the 
greater  will  be  the  satisfaction  in  using  the  blowpipe. 

The  jets  should  be  at  least  half  an   inch   long    and 

FIG.  71. 


coned  into  the  blowpipes,  as  shown  in  fig.  71,  not  screwed 
as  is  generally  the  case. 

To  obtain,  therefore,  the  necessary  internal  shape  for 
satisfactory  blowpipe  jets,  too  much  care  cannot  be  taken 
over  the  work  of  drilling,  which  operation  can  only  be 
successfully  performed  by  means  of  a  specially  constructed 
drill. 

Any  kind  of  flame  may  be  used  for  the  blowpipe,  pro- 
vided it  be  not  too  small ;  a  candle,  a  lamp,  or  gas  may 
be  employed ;  Engestrom  and  Bergman  used  common 
candles  in  preference.  Berzelius  employs  a  lamp,  which 
is  certainly  much  preferable  to  a  candle.  I  have  occasion- 
ally employed  the  flame  of  coal  gas,  which  answers  very 
well,  but  is  not  so  good  as  that  of  a  lamp.  Berzelius  says 
on  this  subject:  'Lamps  have  doubtless  many  advantages 


-206  USING    THE    BLOWPIPE. 

over  candles,  but  are  not  so  convenient  in  travelling,  on 
account  of  the  escape  of  oil.  The  oil  employed  ought  to 
be  the  best  olive  or  salad  oil. 

The  lamp  recommended  by  Mr.  Forbes  has  the  ad- 
vantage of  being  portable,  and  closes  in  such  a  manner 
that  no  oil  can  escape.  It  is  made  of  japanned  tin-plate, 
and  is  about  4  inches  long  and  1  inch  wide,  furnished  at 
one  end  with  a  wick-holder,  capable  of  being  completely 
closed  by  a  screw,  and  at  the  other  with  a  ring  of  tin-plate, 
which  passes  over  the  upright  end  of  a  support.  It  may 
be  mentioned  that  the  screw-cap  is  furnished  with  a 
leather  washer,  by  the  aid  of  which  it  can  be  rendered 
much  tighter,  and  the  escape  of  oil  entirely  prevented. 

Mr.  Forbes  says  that  olive  oil,  burnt  in  the  usual  Ber- 
zelius  blowpipe  lamp,  is  probably  superior  to  any  other. 
Gas  is  not  to  be  recommended,  as  it  is  difficult  to  obtain  a 
good  reducing  flame  when  using  it.  For  cupellation  and 
such  other  operations,  however,  which  only  require  an 
oxidising  flame,  it  is  excellent. 

A  spirit-lamp  may  sometimes  be  employed  in  blowpipe 
assays,  particularly  when  glass  tubes  are  employed,  as  in 
the  detection  of  volatile  substances.  In  these  cases  it  is 
much  more  convenient ;  as  an  oil  lamp,  in  the  first  place, 
blackens  the  tube ;  and  secondly,  does  not  yield  sufficient 
heat,  except  when  the  blowpipe  blast  is  employed. 

It  is  very  difficult  to  describe  in  writing  a  method 
wher  eby  a  student  may  acquire  the  practice  of  using  the 
mouth-blowpipe  ;  that  given  by  Faraday  *  is  perhaps  the 
clearest  and  most  concise.  He  says,  'The  practice  neces- 
sary, in  the  first  place,  is  that  of  making  the  mouth  replace 
the  lungs  for  a  short  time,  by  using  no  other  air  for  the 
blowpipe  than  that  contained  in  it.'  This  practice  is  sim- 
ple in  itself,  and  easy  to  acquire,  but,  as  before  stated, 
difficult  to  describe.  Let  the  student  first  observe  that  it 
is  easy  after  having  closed  the  lips  to  fill  the  mouth  with 
air,  and  to  retain  it  so,  at  the  same  time  respiration  may 
be  carried  on  ;  and  if,  while  the  mouth  is  in  this  state,  a 
blowpipe  be  introduced  between  the  lips,  it  will  be  found 

*  l  Chemical  Manipulation.' 


USING   THE   BLOWPIPE.  207 

that  the  small  quantity  of  air  which  its  jet  allows  to  pass 
through  it  will  be  amply  supplied  for  ten  or  fifteen 
seconds  by  the  quantity  contained  in  the  mouth  ;  and  this 
being  repeated  a  few  times,  a  ready  facility  for  using  the 
blowpipe,  independent  of  the  lungs,  will  be  acquired. 

This  step  being  taken,  the  next  is  to  combine  this  pro- 
cess with  the  ordinary  one  of  propelling  air  directly  from 
the  lungs  through  the  mouth,  in  such  a  way  that  when 
the  action  of  the  lungs  is  suspended  during  inspiration, 
the  blast  may  be  continued  by  the  action  of  the  mouth 
itself,  from  the  air  contained  within  it.  The  time  of  four- 
teen or  fifteen  seconds,  during  which  the  mouth  can  supply 
air  independently  of  the  lungs,  is  far  more  than  that  re- 
quired for  one  or  even  many  more  inspirations;  and  all 
that  is  required  to  acquire  the  necessary  habit  is  the  power 
•of  opening  and  closing  the  communication  between  the 
mouth  and  the  lungs,  and  between  the  air  and  the  lungs, 
at  pleasure. 

The  capability  of  closing  the  passages  to  the  nostrils  is 
very  readily  proved  :  everyone  possesses  and  uses  it  when 
he  blows  from  the  mouth,  and  that  of  closing  or  opening 
the  mouth  to  the  lungs  may  be  acquired  with  equal  readi- 
ness. Applying  the  blowpipe  to  the  lips  as  before,  use  the 
air  in  the  mouth  to  produce  a  current,  and,  when  it  is 
about  half  expended,  open  the  lungs  to  the  mouth,  so  as 
to  replace  the  air  which  has  passed  through  the  blowpipe  ; 
again  cut  off  the  supply,  as  at  first,  but  continue  to  send 
-a  current  through  the  instrument,  and,  when  the  second 
mouthful  of  air  is  gone,  renew  it  as  before  from  the  lungs. 

To  some  this  may  be  difficult ;  but  if  the  preceding 
instructions  be  followed  and  persevered  in  for  a  short  time, 
the  learner  will  soon  find  that  he  can  keep  up  a  continuous 
blast  from  ten  minutes  to  a  quarter  of  an  hour,  without 
any  other  inconvenience  than  the  mere  lassitude  of  the 
lips,  caused  by  compressing  the  mouthpiece  of  the  instru- 
ment, and  this  may  be  avoided  by  using  the  trumpet  mouth- 
piece as  recommended  by  Mr.  Forbes. 

After  having  conquered  the  difficulty  of  keeping  up  a 
continuous  blast,  the  student  must  learn  how  to  attain  the 


208  KEDUCTION   AND    OXIDATION. 

maximum  of  heat  with  the  least  exertion  to  himself.  The 
chief  points  to  be  observed  are,  neither  to  blow  too 
fiercely  nor  too  gently  ;  in  the  first  case,  the  force  of  the 
blast  would  carry  away  heat  by  the  quantity  of  cold  air 
thrown  into  the  flame,  and,  in  the  second,  a  sufficient  amount 
of  heat  would  not  be  obtained  ;  because  a  less  amount  of 
air  would  pass  into  the  flame  than  that  required  for  per- 
fect combustion. 

The  highest  degree  of  temperature  is  required  in  test- 
ing the  fusibility  of  many  bodies,  as  also  in  the  reduction  of 
certain  oxides,  as  those  of  iron,  tin,  &c.  We  have  yet 
another  class  of  phenomena  to  describe,  which  do  not 
essentially  depend  on  a  high  temperature ;  these  are  the 
processes  of  reduction  and  oxidation.  In  order  to  explain 
and  point  out  the  best  methods  of  effecting  these  two 
objects,  it  will  be  necessary  to  enter  somewhat  into  the 
nature  of  flame  :  this  will  be  done  as  briefly  as  is  consis- 
tent with  perspicuity.  The  species  of  flame  examined 
will  be  that  of  a  candle,  as  it  is  a  similar  one  to  that 
with  which  the  blowpipe  operator  will  have  to  experi- 
ment. 

On  careful  examination,  it  will  be  found  that  the  flame 
of  a  candle  or  lamp  may  be  divided  into  four  distinct  por- 
tions :  first,  a  deep  blue  ring  at  the  base ;  this  consists  of 
the  vapour  of  the  combustible,  which  can  hardly  burn 
because  it  has  not  acquired  a  sufficient  temperature ; 
secondly,  a  dark  cone  in  the  centre  ;  this  is  also  the  vapour, 
but  heated  intensely,  not,  however,  in  a  state  of  combus- 
tion, on  account  of  the  absence  of  air  ;  thirdly,  of  a  very 
brilliant  envelope,  which  surrounds  the  dark  parts  just 
mentioned  ;  this  is  the  partially  consumed  vapour  at  a  very 
high  temperature ;  the  luminous  property  it  possesses  is 
due  to  the  precipitation  and  subsequent  ignition  of  par- 
ticles of  solid  carbon  ;  and  fourthly,  of  an  almost  invisible 
envelope  which  surrounds  the  luminous  portion  ;  this  is 
the  substance  of  the  combustible  in  full  ignition,  it  here 
mingles  with  the  atmospheric  oxygen,  and  is  consumed. 
The  highest  degree  of  temperature  in  the  whole  flame  is 
to  be  found  at  the  point  of  contact  between  the  luminous 


SEDUCTION   AND    OXIDATION.  209 

and  this  part.  It  must  be  particularly  borne  in  mind  that 
the  inner  portions  of  the  flame  have  an  excess  of  carbonace- 
ous matters,  and  the  outer  an  excess  of  oxygenated  matters. 
Having  premised  this  much,  we  will  examine  the  nature 
of  the  flame  of  a  candle  when  acted  on  by  the  blowpipe 
blast,  and  ascertain  how  far  it  is  altered,  and  what  are  the 
properties  of  its  separate  parts  in  relation  to  their  oxidis- 
ing and  reducing  powers.  Supposing  the  lighted  lamp  or 
candle  be  ready  and  neatly  snufled,  place  the  nozzle  of  the 
blowpipe  just  in  the  edge  of  the  flame,  and  about  the  six- 
teenth of  an  inch  above  the  level  of  the  wick :  when 
things  are  in  this  state,  blow  gently  and  evenly  through 
the  blowpipe,  and  a  conical  jet  or  dart  of  flame  will  be 
produced,  which,  when  formed  in  a  steady  atmosphere, 
free  from  accidental  draughts  and  currents,  will  be  found 
to  consist  of  two  essential  parts — the  inner  cone,  blue, 
small,  and  well-defined ;  the  outer,  brownish  and  vague. 
The  greatest  intensity  of  heat  is  found  a  little  beyond  the 
apex  of  the  blue  flame  ;  it  is  there,  also,  reduction  takes 
place.  The  outer  flame  is  formed  by  the  complete  com- 
bustion of  the  combustible  matter  of  the  inner ;  and  at  that 
place,  and  just  beyond  it,  oxidation  takes  place. 

Oxidation,  as  before  stated,  takes  place  at  the  extremity 
of  the  outer  flame,  hence  it  is  termed  the  oxidising  flame  ; 
in  it  all  the  combustible  portions  are  supersaturated  with 
oxygen.  In  general  the  further  the  substance  to  be  oxidised 
can  be  placed  from  the  extremity  of  the  flame,  the  better 
the  operation  proceeds,  provided  always  that  the  necessary 
temperature  be  maintained.  Dull  redness  is  the  best  suited 
for  oxidation. 

Reduction. — In  this  operation  the  jet  of  the  blowpipe 
must  be  introduced  into  the  body  of  the  flame,  so  as  only 
to  produce  a  small  dart ;  and  a  jet  having  a  smaller  hole 
than  that  used  for  oxidation  ought  to  be  employed.  By 
operating  thus,  a  more  brilliant  flame  than  the  last  is  pro- 
duced ;  it  is  the  result  of  a  less  perfect  combustion,  and 
therefore  contains  a  large  amount  of  carbonaceous  matter,, 
fitting  it  more  especially  for  the  purpose  of  separating  oxy- 
gen from  all  metallic  bodies. 

p 


210  AUXILIARY   BLOWPIPE    APPARATUS. 

Berzelius  says,  '  the  most  important  point  in  blowpipe 
assays  is  the  power  of  producing  oxidation  and  reduction 
at  will.'  Oxidation  is  so  easy,  that  to  do  it  requires  only 
to  read  a  description  of  it ;  but  reduction  requires  some 
practice,  and  a  certain  knowledge  of  producing  various 
kinds  of  blasts.  One  of  the  best  methods  of  exercise  in 
this  operation  is  to  take  a  small  grain  of  tin,  and  place  it 
on  charcoal ;  then  direct  the  blowpipe  dart  upon  it — it 
will  soon  fuse ;  and  if  the  operator  has  not  produced  a 
good  reducing  flame,  it  will  become  covered  with  a  crust 
of  oxide ;  so  that  it  becomes  a  witness  against  him  each 
time  this  happens.  The  nature  of  the  flame  must  be  altered 
until,  by  observation,  the  proper  kind  is  produced  at  will. 
The  longer  the  button  of  tin  is  kept  bright,  the  better  and 
more  expert  the  operator. 

AUXILIARY   BLOWPIPE   APPARATUS,    ETC. 

Supports. — The  support  is  the  substance  destined  to 
hold  the  material  to  be  assayed  whilst  under  the  influence 
of  heat.  From  this  it  will  be  seen  that  an  exceedingly  re- 
fractory body  must  necessarily  be  employed,  so  as  not  to 
give  way  under  the  excessive  heat ;  and  also  (with  the 
exception  of  charcoal),  it  ought  to  have  no  chemical  action 
on  the  substances  placed  in  contact  with  it.  Supports 
may  be  divided  into  combustible  and  incombustible ; 
the  former  is  charcoal,  and  for  the  latter,  metal,  glass, 
and  earthenware,  and  in  some  cases  certain  minerals  have 
been  employed. 

Charcoal. — Mr  Forbes  gives  the  following  excellent 
'description  of  the  preparation  of  charcoal  for  blowpipe 
purposes.  '  It  is  extremely  difficult  to  obtain,  in  England, 
charcoal  fit  for  blowpipe  operations,  without  special  pre- 
paration. The  charcoal  sold  is  generally  of  hard  wood, 
badly  burnt,  full  of  cracks,  and  decrepitating  upon  appli- 
cation of  heat.  Good  charcoal  should  be  soft,  yet  com- 
pact, and  without  cracks,  and  is  best  made  from  fir  or 
pine.  Where  good  charcoal  cannot  be  obtained  it  can  be 
made  artificially  by  moulding  charcoal  powder  agglutinated 


CHARCOAL    APPAKATUS. 


211 


by  some  starch  paste,  and,  after  desiccation,  burning  the 
pieces  in  a  crucible  filled  with  sand. 

'  For  the  preparation  of  the  charcoal  used  as  a  support 
for  the  assays,  the  instruments  represented  in  fig.  72  are 
required,  all  of  which  are  fitted  in  the  universal  handle  a, 
which  is  shown  in  this  figure  FlG  72 

as  holding  the  largest  charcoal 
borer,  a  section  and  plan  of 
which  are  shown  in  b.  This 
large  borer  is  employed  for 
forming  the  deep  holes  in  the 
charcoal  used  in  the  blowpipe 
furnace,  and  which  serve  to 
contain  the  clay  crucibles  or 
capsules  in  which  the  assays 
are  fused.  The  blast  holes  in 
the  charcoal  inside  the  blowpipe 
furnace  are  bored  out  by  the 
gouge-shaped  borer  d,  which 
also  serves  for  making  small 
holes  or  grooves  in  charcoal  for 
general  purposes.  The  smaller 
borer  c,  is  most  useful,  particularly  in  boring  out  the  holes 
for  receiving  the  soda  paper  cornets  containing  the  assay 
for  reduction.  The  saw-knife  e  also  fits  into  the  same 
handle,  and  is  used  for  trimming  and  sawing  across  the 
charcoal  pieces,  having  coarse  saw-teeth  in  front,  whilst 
the  back  presents  a  sharp  knife-edge.  The  figures  are 
all  drawn  to  one-half  of  the  real  size/ 

Platinum. — This  metal  is  much  employed  as  a  support 
in  cases  where  charcoal  would  be  injurious  by  its  reducing 
power.  It  is  used  in  three  forms,  viz.  wire,  foil,  and  as  a 
spoon,  or  small  capsule. 

Wire. — A  moderately  strong  wire  of  platinum,  about  2 
inches  long,  and  curved  at  one  end,  is  used  with  great 
advantage  in  many  quantitative  examinations.  The  curve 
serves  as  a  support  in  all  experiments  on  tests  of  oxidation 
and  reduction,  where  alteration  of  colour  only  is  to  be 
observed.  This  support  can  be  relied  on,  for  it  is  totally 

p  2 


212  GHAECOAL   APPAKATUS. 

free  from  the  false  varieties  of  colour  which  are  too  often 
perceptible  when  the  assay  rests  on  charcoal.  In  the 
treatment  of  metals,  or  in  reduction  tests,  where  an  easily 
melted  body  is  to  be  operated  upon,  charcoal  must,  how- 
ever, be  used.  It  is  necessary  to  have  at  hand  several 
platinum  wires,  so  as  to  proceed  to  another  experiment 
without  being  obliged  to  forcibly  remove  the  adhering 
borax  glass,  or  to  wait  for  its  solution  in  hydrochloric 
acid,  which  is  the  better  mode.  If  the  platinum  loop 
melts  with  the  reagent,  it  must  be  cut  away,  and  a  new 
one  formed.  A  wire  can  be  used  for  a  very  long  timey 
and  when  it  becomes  too  short  to  be  held  between  the 
fingers  the  straight  end  may  be  fastened  into  a  cork,  or  a 
piece  of  glass  tubing. 

The  platinum  spoon  (see  fig.  73)  and  foil  are  used  in 
much  the  same  way  ;  but  as  charcoal  and  the  platinum  wire 
Fl°-  78-  answer  every  purpose,  it 

will  be  unnecessary  to  de- 
scribe their  use  further  : 
small  iron  spoons  of  the 
above  form  are  also  madey 
and  are  very  useful  in 
cases  where  the  presence 
of  iron  is  not  objectionable. 
Other  instruments,  as  forges,  hammer,  anvil,  agate 
mortar,  scissors,  &c.,  are  sufficiently  familiar  to  every- 
body not  to  require  description.  Special  apparatus 
required  for  any  operation  will  be  described  in  the  course 
of  the  processes. 

Colonel  Eoss  recommends  as  a  support  in  certain  cases 
a  thin  rectangular  slip  of  aluminium  plate,  4  inches  by  2, 
half  an  inch  of  the  lower  end  of  which  is  turned  up  at  an 
angle  of  80°  as  a  rest  for  the  assay.  A  fragment  of  the 
substance  of  the  size  of  a  pea  is  laid  upon  the  edge  close 
to  the  angle,  and  heated  very  slightly  about  half  an  inch 
from  the  top  of  a  pure  blue  flame.  The  sublimate  obtained 
should  be  examined  from  time  to  time,  increasing  the  heat 
after  each  examination,  till  nothing  more  is  obtained. 

For  a  full  description  of  this  method,  by  means  of  which 


BLOWPIPE    REAGENTS   AND    FLUXES.  213 

substances  existing  in  mixture  or  combination  may  be 
usefully  separated  by  taking  advantage  of  their  different 
degrees  of  volatility,  the  reader  is  referred  to  '  Alphabetical 
Manual  of  Blowpipe  Analysis  '  (Triibner  &  Co.). 

Asbestos  card-board,  according  to  Mr.  W.  M.  Hartley, 
may  also  serve  for  supports.  This  substance  resembles 
greyish  cardboard,  but  has  a  soapy  feel,  like  steatite ;  it 
can  be  used  for  making  crucible-supports,  sand-baths, 
muffles,  retort-supports,  etc. ;  it  can  be  cut  with  cork 
borers  or  scissors ;  by  moistening  with  water  it  can  be 
moulded  to  any  shape.  After  moistening  it  should  be 
gradually  dried  and  ignited,  to  get  rid  of  organic  matter. 
It  stands  the  ordinary  wear  and  tear  of  the  laboratory 
well.  It  is  formed  principally  of  asbestos  fibres.  It  can 
be  obtained  from  the  manufactory,  31,  St.  Vincent  Place, 
Glasgow,  at  4s.  a  pound. 

REAGENTS   AND    FLUXES. 

BLUE  LITMUS  PAPEE  is  used  for  detecting  free  acid  in 
solution,  its  colour  being  changed  to  red. 

REDDENED  LITMUS  PAPEE  is  used  for  the  detection  of  free 
alkali,  its  colour  being  restored  to  blue. 

BBAZIL-WOOD  PAPEE  is  used  for  detecting  hydrofluoric 
acid,  being  tinged  straw-yellow  when  immersed  in  a  very 
dilute  solution  of  this  acid. 

TUEMEEIC  PAPEE  is  used  for  detecting  free  alkalies  :  the 
change  produced  is  very  characteristic,  its  bright  yellow 
colour  becoming  dark  brown. 

NITEIC  ACID  is  employed  in  the  solution  of  various 
metals,  alloys,  and  ores,  and  for  the  discrimination  of 
certain  precipitates  ;  also  as  an  oxidising  agent. 

ZINC  is  principally  employed  for  the  reduction  of  anti- 
mony and  tin. 

COPPEE  is  used  for  the  reduction  of  mercurial  salts  and 
for  the  detection  of  arsenious  acid.  It  is  also  used  to 
detect  the  presence  of  nitric  acid. 

IEON  WIEE  is  employed  to  precipitate  many  metals,  and 
in  the  separation  of  sulphur  and  the  fixed  acids  from  any 


214          BLOWPIPE  REAGENTS  AND  FLUXES. 

substance  with  which  they  may  be  combined.  The  metals 
which  can  thus  be  precipitated,  or  deprived  of  sulphur, 
are  copper,  lead,  nickel,  and  antimony.  For  instance,  if  a 
small  piece  of  iron  (pianoforte)  wire  be  placed  in  a  sub- 
stance in  fusion,  and  acted  upon  by  the  blowpipe,  it 
becomes  covered  with  the  reduced  metal.  The  latter 
sometimes  appears  as  small  globules. 

Iron  has  the  property  of  reducing  phosphorus  from 
phosphoric  acid  or  the  phosphates,  giving  rise  to  a  phos- 
phide of  iron,  which  forms  on  fusion  a  white,  brittle, 
metallic  globule. 

POTASSIUM  CYANIDE. — This  is  a  most  useful  flux.  MM. 
Haidlen  and  Fresenius  say  :  '  We  have  examined  its  action 
on  many  oxides,  sulphides,  salts,  &c.,  in  reference  to  its 
use  as  a  reagent  combined  with  the  blowpipe.  We  prefer, 
in  general,  a  mixture  of  equal  parts  of  anhydrous  soda 
and  potassium  cyanide.  This  mixture  was  employed  on 
account  of  the  great  facility  with  which  the  pure  cyanide 
fuses.  It  acts,  in  general,  so  very  similarly  to  pure  soda, 
that  it  would  be  superfluous  to  describe  singly  the  changes 
which  each  individual  body  appeared  to  undergo  when 
exposed  to  its  action.  We  cannot,  however,  pass  over  the 
following  especial  advantages  which  it  possesses  as  com- 
pared  with  soda.  First,  reductions  are  obtained  with  such 
great  facility  that  the  least  practised  operator  may  execute 
reductions  which  would  otherwise  be  very  difficult ;  for 
instance,  the  reduction  of  tin  from  either  its  oxide  or 
sulphide ;  and,  secondly,  that  the  fused  mixture  of  potas- 
sium cyanide  with  soda  is  so  easily  absorbed  by  the  char- 
coal, that  the  grains  of  reduced  metal  can  always  be  most 
distinctly  perceived,  and  may  be  most  easily  separated 
therefrom  for  further  examination.' 

SODIUM  CARBONATE,  called,  for  the  sake  of  brevity,  SODA. 
— The  plain  carbonate  or  the  bicarbonate  may  be  in- 
differently employed  ;  but  in  either  case  it  is  absolutely 
necessary  that  it  be  free  from  sulphates. 

There  are  two  objects  in  view  in  the  employment  of 
soda  as  an  auxiliary  to  the  blowpipe ;  first,  to  ascertain  if 
the  substances  combining  with  this  body  be  fusible  or  infu- 


BEAGENTS   IN   THE   DRY   WAY*  215 

sible ;  and  secondly,  to  facilitate  the  reduction  of  certain 
metallic  oxides. 

In  the  fusion  of  substances  with  Soda  there  are  many 
things  to  observe.  The  necessary  quantity  must  be  taken 
on  the  moistened  point  of  a  knife,  and  kneaded  in  the  palm 
of  the  hand,  so  that  it  may  form  a  coherent  mass.  If  the 
body  under  examination  be  pulverulent  it  must  be  incor- 
porated with  it,  but  if  in  lump  it  must  be  placed  upon  it, 
forcing  it  slightly  into  the  moistened  soda  ;  then  carefully 
heated  on  the  charcoal  with  a  gentle  flame,  until  thoroughly 
dry  ;  and  lastly  it  may  be  fused.  It  generally  happens 
that  the  soda,  at  the  instant  of  fusion,  is  absorbed  by  the 
charcoal ;  but  this  does  not  hinder  its  action  on  the  assay ; 
for  if  it  be  fusible  with  soda,  the  latter  comes  to  the  surface 
and  attacks  it,  finally  forming  a  liquid  globule.  If  the 
substance  be  infusible  in  soda,  but  decomposable  by  it,  it 
alters  its  appearance  without  entering  into  fusion.  But, 
however,  before  pronouncing  any  substance  to  be  infusible 
by  soda,  the  flux  ought  to  be  mixed  with  the  pulverised 
substance.  If  in  these  trials  too  little  soda  be  taken,  a 
portion  of  the  substance  remains  solid,  and  the  rest  forms 
a  covering  of  transparent  glass  ;  if  too  much,  the  bead  of 
glass  becomes  opaque  on  cooling.  It  sometimes  happens 
that  the  assay  contains  a  substance  which,  being  insoluble 
in  the  glass  of  soda,  prevents  it  becoming  transparent. 
Then,  in  order  that  we  may  fall  into  no  error  respecting 
the  nature  of  the  glass,  it  becomes  necessary  in  the  two 
last-mentioned  cases  to  add  a  new  quantity  of  the  body 
under  examination,  and  then  ascertain  if  a  limpid  globule 
cannot  be  obtained.  In  general  it  is  the  best  method  to 
add  the  soda  by  successive  small  doses,  and  note  the 
changes  produced  by  each  addition.  It  sometimes  happens, 
in  this  kind  of  assay,  that  the  glass  becomes  coloured  at 
the  moment  of  cooling,  and  finally  takes  a  yellow  or  deep 
hyacinth  red  ;  it  even  becomes  occasionally  opaque  and 
yellowish-brown.  These  phenomena  indicate  the  presence 
of  sulphur,  either  in  the  assay  or  the  soda  employed.  If 
the  same  colour  be  constantly  produced  by  the  same  soda, 
it  is  a  proof  that  it  contains  sulphate  of  soda  ;  it  must  then 


216  REDUCTION   BEFORE   THE   BLOWPIPE. 

be  discarded,  but  if  it  gives  generally  a  colourless  glass,  it 
is  the  substance  under  assay  that  contains  -sulphur  or  sul- 
phuric acid. 

Reduction  of  Metallic  Oxides. — This  species  of  assay, 
by  which  quantities  of  reducible  metals,  so  small  as  to 
escape  ordinary  wet  analyses,  can  be  detected,  is  the  most 
important  discovery  Gahn  made  in  the  application  of  the 
blowpipe. 

If  a  small  quantity  of  native  or  artificial  oxide  of  tin 
be  placed  on  charcoal,  it  requires  a  long  blast  and  a  skil- 
ful operator  to  produce  a  grain  of  metallic  tin  ;  but  if  a 
small  quantity  of  soda  be  added,  the  reduction  takes  place 
readily,  and  so  completely  with  pure  oxide,  that  the  whole 
is  transformed  into  a  button  of  tin.  From  this  it  is 
certain,  that  the  presence  of  soda  favours  the  decom- 
position. 

The  action,  however,  can  be  explained  thus,  as  Berzelius 
himself  hints  :  the  red-hot  charcoal  reacts  upon  the  sodium 
carbonate,  producing  by  its  reduction  a  certain  amount  of 
sodium,  which  by  its  strong  attraction  for  oxygen  seizes  on 
that  contained  by  the  metallic  oxide  which  is  required  to 
be  reduced.  If  the  metallic  oxide  contain  an  unreducible 
substance,  the  reduction  of  the  former  becomes  difficult ; 
but  if  a  little  borax  be  added,  the  reduction  takes  place  as 
usual. 

This  assay  is  very  easy  of  execution,  and  the  metal  is 
readily  recognised,  as  by  previous  assays  the  nature  of  it  is 
somewhat  ascertained,  and  the  reduction  but  confirms  the 
previous  idea. 

If  the  metallic  oxide  be  mixed  with  such  a  quantity  of 
non-reducible  substances  that  its  nature  cannot  be  ascer- 
tained by  previous  experiment,  how  can  it  be  proved  that 
a  reducible  metal  is  present  ? 

Gahn  has  solved  this  question  in  a  very  simple  manner. 
4  After  having  pulverised  the  substance  to  be  assayed,  it 
is  kneaded  in  the  palm  of  the  hand  with  moistened  soda, 
and  the  mixture  placed  on  charcoal  and  exposed  to  a  good 
reducing  flame ;  a  little  more  soda  is  then  added,  and  the 
blast  recommenced.  As  long  as  any  portion  of  the  sub- 


REDUCTION   BEFORE   THE    BLOWPIPE.  217 

stance  remains  on  the  charcoal,  soda  is  added  in  small  por- 
tions, and  the  blast  continued  until  the  charcoal  has  ab- 
sorbed the  whole  of  the  mass.  The  first  quantities  of  soda 
serve  to  collect  the  metallic  particles  scattered  in  the  sub- 
stance to  be  assayed,  and  the  final  absorption  of  the  latter 
completes  the  reduction  of  any  that  may  remain  in  the  state 
•of  oxide. 

'  This  done,  the  burning  charcoal  is  extinguished  with 
a  few  drops  of  water ;  then  having  cut  out  the  part  which 
absorbed  the  soda  and  assay,  grind  it  to  a  very  fine  powder 
in  an  agate  mortar.  This  powder  is  then  washed  with 
water  to  carry  away  the  finest  portion  of  the  charcoal. 
The  grinding  and  washing  are  repeated  until  all  the  char- 
coal is  washed  away.  If  the  substance  contained  no 
metallic  body,  nothing  will  remain  in  the  mortar  after  this 
last  washing.  But  if  it  contained  the  smallest  quantity  of 
reducible  matter,  it  is  found  at  the  bottom  of  the  mortar, 
as  small  brilliant  plates  if  it  be  malleable,  or  as  a  fine  pow- 
der if  it  be  brittle  or  not  fusible.  In  either  case,  the  bottom 
of  the  mortar  is  covered  by  metallic  traces,  resulting  from 
the  friction  of  the  particles  of  metal  against  its  sides  (pro- 
vided that  the  quantity  of  metal  contained  in  the  sample 
be  not  too  small).  The  flattening  of  almost  imperceptible 
globules  of  any  malleable  metal  converts  them  into  shining 
discs  of  a  perceptible  diameter.  In  this  manner  may  be 
discovered  by  the  blowpipe,  in  an  assay  of  ordinary  size, 
less  than  a  half  per  cent,  of  tin,  and  even  less  than  that  of 
copper.' 

The  following  points  in  this  class  of  assay  ought  to  be 
particularly  attended  to.  First,  to  produce  the  strongest 
possible  flame,  taking  care  that  it  covers  every  part  of 
the  assay.  Secondly,  to  leave  none  of  the  metal  in  the 
charcoal,  or  lose  the  smallest  quantity  in  the  collection. 
Thirdly,  to  well  grind  the  carbonaceous  mass.  Fourthly, 
to  decant  very  slowly,  so  that  only  the  lighter  parts  may 
be  carried  away  by  the  water.  Fifthly,  not  to  judge  of  the 
result  until  the  whole  of  the  charcoal  has  been  removed, 
for  a  small  quantity  remaining  suffices  to  hide  the  metallic 
particles  ;  and,  moreover,  the  particles  of  charcoal,  viewed 


218  BORAX. 

in  a  certain  light,  have  themselves  a  metallic  lustre,  which 
will  deceive  an  inexperienced  eye.  Sixthly,  and  lastly y 
not  to  trust  to  the  naked  eye,  however  plain  the  sample 
may  be,  but  always  examine  by  the  aid  of  a  good  micro- 
scope. 

The  metals  reducible  by  this  process  are  (besides  the 
noble  metals),  molybdenum,  tungsten,  antimony,  tellurium, 
bismuth,  tin,  lead,  thallium,  copper,  nickel,  cobalt,  and 
iron.  Amongst  these,  antimony,  bismuth,  thallium,  and 
tellurium  volatilise  easily  when  they  are  exposed  to  a 
strong  heat.  Selenium,  arsenic,  cadmium,  zinc,  and  mer- 
cury volatilise  so  completely  that  they  cannot  be  collected 
except  by  means  of  a  small  subliming  apparatus. 

The  reduction  can  always  be  effected  the  first  time- 
when  the  assay  contains  from  8  to  10  per  cent,  of  metal; 
but  in  proportion  as  the  standard  decreases  more  attention 
and  care  must  be  paid  to  the  washing  and  recognition  of 
the  reduced  metal  in  the  mortar.  A  good  system  of  prac- 
tice in  this  experiment  is  to  employ  any  cupreous  sub- 
stance, and  make  on  it  a  great  number  of  experiments, 
taking  care  to  mix  it  each  time  with  a  substance  contain- 
ing no  copper ;  thus  the  metallic  value  will  diminish  at 
each  new  assay,  until  at  last  no  copper  can  be  found. 

If  the  substance  to  be  assayed  contains  several  metals, 
the  reduction  of  their  oxides  must  be  made  in  globo,  and 
a  metallic  alloy  obtained.  Some,  small  in  number,  are 
reduced  separately.  For  instance,  copper  and  iron  give  a 
regulus  of  each  metal ;  copper  and  zinc,  the  first  gives  a 
regulus  of  copper,  whilst  the  latter  volatilises.  But  when 
the  result  of  the  operation  is  an  alloy,  recourse  must  be  had 
to  the  reactions  produced  by  other  fluxes  to  ascertain  its 
constituents. 

BORAX  (SODIUM  BIBORATE). — The  borax  of  commerce 
must  be  dissolved  in  hot  water  and  recrystallised,  before  it 
can  be  used  in  blowpipe  analysis. 

Borax  may  be  employed  either  in  crystals,  the  requisite 
size  for  an  assay,  or  in  a  pulverulent  form  ;  in  this  case  it 
may  be  taken  up  on  the  moistened  point  of  a  knife.  Some 
operators  prefer  fusing  the  borax  before  use,  in  order  to 


FUSION   WITH   BORAX.  21& 

drive  off  its  water  of  crystallisation,  and  thus  avoid  the 
tumefaction  of  the  crystal  on  charcoal. 

Borax  is  employed  in  the  solution  or  fusion  of  a  variety 
of  substances.  It  is  best  to  commence  by  acting  upon  a 
scale  of  the  substance  to  be  examined ;  because  if  a  pow- 
der be  employed  the  resulting  action  cannot  be  so  well 
ascertained.  The  following  phenomena  are  to  be  carefully 
watched,  for  in  treating  any  substance  with  borax  it  must 
be  particularly  noted  whether  the  fusion  takes  place  rapidly 
or  otherwise ;  without  motion  or  with  effervescence  ;  if 
the  glass  resulting  from  the  fusion  is  coloured,  and  if  that 
colour  changes  in  the  oxidising  or  reducing  flame  ;  and, 
lastly,  if  the  colour  diminishes  or  increases  on  cooling,  and 
if,  under  the  same  circumstances,  it  loses  or  retains  its 
transparency. 

Some  substances  possess  the  property  of  forming  a 
limpid  glass  with  borax,  which  preserves  its  transparency 
on  cooling,  but  which,  if  slightly  heated  in  the  exterior 
(oxidising)  flame,  becomes  opaque  and  milk-white,  or 
coloured  when  the  flame  strikes  it  in  an  unequal  or  inter- 
mittent manner.  The  alkaline  earths,  as  yttria,  glucina, 
zirconia  ;  the  oxides  of  cerium,  tantalum,  titanium,  &c.y 
belong  to  this  class.  In  order  to  be  certain  of  this  result 
we  must  assure  ourselves  that  the  glass  is  saturated  to 
a  certain  point  with  either  of  the  above  class  of  bodies. 
The  same  thing,  however,  does  not  happen  with  silica, 
alumina,  iron,  manganese,  &c.,  oxides,  and  the  presence  of 
silica  prevents  the  production  of  this  phenomenon  with  the 
earths  ;  so  that  alone  they  present  this  peculiar  appearance 
with  borax ;  but  when  combined  with  silica  (as  natural 
silicates,  for  instance),  no  such  effect  is  produced.  This 
operation  has  received  the  name  of  flaming,  and  any 
substance  thus  acted  upon  is  said  to  become  opaque  by 
flaming. 

SODIUM  AMMONIA-PHOSPHATE  (MICROCOSMIC  SALT)  is  obtained 
by  dissolving  16  parts  of  sal-ammoniac  in  a  very  small 
quantity  of  boiling  water,  and  mixing  with  it  100  parts  of 
crystallised  sodium  phosphate,  dissolving  the  whole  with 
heat,  filtering  the  boiling  liquid  ;  during  cooling  the  double 


220  FUSION   WITH   MICEOCOSMIC   SALTS. 

salt  crystallises.  When  microcosmic  salt  is  not  pure  it 
forms  a  glass  which  becomes  opaque  by  cooling.  It  is  then 
necessary  to  dissolve  it  in  a  small  quantity  of  water  and 
recrystallise  it. 

It  may  be  collected  in  large  crystals,  or  in  a  pulverulent 
state.  The  crystals  are  in  general  of  a  suitable  size  for 
ordinary  assays.  Placed  on  charcoal,  and  submitted  to  the 
blowpipe  flame,  it  bubbles  and  swells  up,  giving  off  am- 
monia ;  that  which  remains  after  this  treatment  is  an  acid 
sodium  phosphate,  which  fuses  readily,  and  forms  on  cool- 
ing a  transparent  and  colourless  glass.  As  a  reagent,  it 
acts  principally  by  its  free  phosphoric  acid  ;  and  if  the  salt 
be  employed  in  preference  to  the  acid,  it  is  because  it  is 
less  deliquescent,  costs  less,  and  passes  readily  into  the 
charcoal.  By  means  of  microcosmic  salt  we  ascertain 
the  action  of  free  acids  on  any  substance  we  may  wish  to 
assay.  The  excess  of  acid  it  contains  combines  with  all 
bases,  and  forms  a  class  of  double  salts,  more  or  less  fusible, 
which  are  examined  as  to  their  transparency  and  colour. 
In  consequence,  this  flux  is  used  more  particularly  in  the 
detection  of  the  metallic  oxides,  most  of  which  impart  to 
it  very  characteristic  colours.  This  flux  exercises  on  acids 
a  repulsive  action.  Those  which  are  volatile,  sublime  ;  and 
those  which  are  fixed  remain  in  the  mass,  dividing  the  base 
with  the  phosphoric  acid,  or  yielding  it  up  entirely ;  in 
which  case  they  are  suspended  in  the  glass  without  being 
dissolved.  In  this  respect,  microcosmic  salt  is  a  good  test 
for  silicates  ;  for  by  its  aid  silica  is  liberated,  and  appears 
in  the  glass  as  a  gelatinous  mass. 

POTASSIUM  NITRATE  (NITRE),  in  long  and  thin  crystals,  is 
employed  in  hastening  the  oxidation  of  those  substances 
which  do  not  readily  combine  with  oxygen  in  the  exterior 
flame.  It  is  used  as  follows  ;  the  point  of  a  crystal  is  thrust 
into  the  fused  bead  ;  but  in  order  to  prevent  the  cooling  of 
the  latter  the  crystal  is  held  by  a  pair  of  pliers,  so  that 
when  the  bead  begins  to  cool  it  may  be  withdrawn,  the 
bead  reheated,  and  the  crystal  employed  as  before,  until 
the  desired  effect  is  produced. 

POTASSIUM  BISULPHATE  is  employed  in  the  detection  of 


FUSION   WITH    BISULPHATES.  221 

lithia,  boracic  acid,  nitric  acid,  hydrofluoric  acid,  bromine, 
and  iodine.  It  separates  baryta  and  strontia  from  the  earths 
and  metallic  oxides. 

SODIUM  BISULPHATE. — Professor  J.  Lawrence  Smith  *  has 
suggested  the  use  of  sodium  bisulphate  as  a  substitute  for 
the  potassium  bisulphate  in  the  decomposition  of  minerals, 
especially  the  aluminous  minerals.  He  finds  that  '  while 
the  soda  salt  gives  a  decomposition  at  least  as  complete  as 
the  potash  salt,  the  melted  mass  is  very  soluble  in  water, 
and  in  the  future  operations  of  the  analyses  there  is  no 
embarrassment  from  a  deposit  of  alum. 

'  The  ordinary  commercial  article  is  not  sufficiently 
pure  for  use,  and  he  prepares  it  from  pure  sodium  carbo- 
nate, or  sodium  sulphate  that  has  been  purified  by  recrys- 
tallisation.  In  either  instance  pure  sulphuric  acid  is 
added  in  excess  to  the  salt  in  a  large  platinum  capsule,  and 
heated  over  a  flame,  until  the  melted  mass,  when  taken 
up  on  the  end  of  a  glass  rod,  solidifies  quite  firmly.  The 
mass  is  then  allowed  to  cool ;  moving  it  over  the  sides  of 
the  capsule  will  facilitate  this  operation.  When  cool  it  is 
readily  detached  from  the  capsule,  is  then  broken  up,  and 
put  into  a  glass  stoppered  bottle.  In  almost  every  instance 
where  we  have  been  in  the  habit  of  using  potassium 
bisulphate  the  sodium  bisulphate  can  be  substituted.' 

VITRIFIED  BOBACIC  ACID  is  used  to  ascertain  the  presence 
of  phosphoric  acid  and  small  portions  of  copper  in  lead 
alloys.  For  quantitative  analysis,  it  is  generally  used  to 
ascertain  the  quantity  of  copper  contained  in  a  lead  ore, 
and  also  the  amount  of  copper  united  with  various  metals. 

COBALT  NITRATE  in  solution  ought  to  be  free  from 
arsenic  and  nickel,  and  the  solution  must  be  moderately 
strong.  It  is  used  as  a  test  for  alumina,  magnesia,  tin,  and 
zinc,  by  the  blowpipe. 

NICKEL  OXALATE  is  used  in  qualitative  examinations  for 
the  detection  of  potash  in  a  salt  which  also  contains  soda 
and  lithia. 

COPPER  OXIDE  is  employed  to  detect  the  presence  of 
hydrochloric  acid  and  chlorine. 

*  'American  Journal  of  Science  and  Arts.' 


222  BONE   ASH. 

SILICA  is,  with  soda,  an  excellent  test  for  the  presence 
of  sulphuric  acid  ;  and  when  in  combination  with  borax  or 
soda,  separates  tin  from  copper. 

TURNER'S  FLUX. — This  is  a  mixture  of  potassium  bisul- 
phate  and  fluor-spar.  It  is  used  for  producing  coloured 
flames  before  the  blowpipe, 

CALCIUM  FLUORIDE  (FLUOR-SPAR),  AND  LIME  SULPHATE 
(GYPSUM). — These  two  bodies  (deprived  of  water)  are  used 
to  indicate  the  presence  of  each  other.  If  a  small  piece  of 
gypsum  be  ignited  in  contact  with  a  similar  piece  of  fluor- 
spar, they  soon  liquefy  at  their  points  of  contact ;  they  then 
combine,  and  form,  by  fusing,  a  colourless  and  transparent 
bead  of  glass,  which  becomes  enamel-white  on  cooling. 
Fluoride  of  calcium  is  thus  employed  as  a  test  for  gypsum, 
and  vice  versd. 

Mr.  S.  D.  Poole  prefers  a  mixture  of  calcium  sulphate 
(selenite)  and  fluor-spar  (in  the  proportions  of  two  parts  of 
the  former  to  one  of  the  latter)  to  Turner's  flux  described 
above.  It  forms  an  easily  fusible  bead,  which  by  itself 
gives  only  a  very  faint  dull  red  tint  (lime)  to  the  flame,  but 
which  renders  the  presence  of  many  elements  which  give 
colour  most  beautifully  evident.  Thus  small  portions  of 
lepidolite,  petalite,  &c.,  mixed  with  this  flux  impart  the 
fine  carmine  tint  of  lithia  ;  copper  or  strontium  their  well- 
known  colours,  especially  after  continued  blowing.  Potash 
and  soda  minerals  (felspar  and  albite)  are  at  once  distin- 
guished. 

This  flux  is  of  more  limited  applicability  than  that  of 
Turner,  because  there  is  no  provision  in  it  for  the  libera- 
tion of  hydrofluoric  acid. 

It  serves,  when  mixed  with  bisulphate  of  potash,  to  de- 
tect lithia  and  boracic  acid  in  their  various  combinations. 

BONE  ASHES  are  employed  in  the  cupellation  of  gold  and 
silver.  Harkort  reduced  them  to  many  states  of  minute 
division  by  the  processes  of  sifting  and  washing.  The  bones 
are  burned  until  they  become  perfectly  white,  and  then 
freed  from  any  carbonaceous  matter  that  may  have  adhered 
to  them.  This  being  done,  they  are  pulverised  in  a  mortar, 
and  the  finer  portions  separated  by  a  sieve.  The  remain- 


LEAD,    TINFOIL.  223 

ing  powder  is  then  thrown  upon  a  filter,  and  treated  with 
boiling  water,  which  extracts  the  soluble  matter.  The 
washing,  which  is  then  resorted  to,  is  for  procuring  the 
bone  ashes  of  a  more  uniform  degree  of  fineness.  The 
mass  from  the  filter  is  mixed  with  water  in  a  cylindrical 
glass,  allowed  to  settle  for  a  few  minutes  and  then  decanted  ; 
the  coarser  powder  is  deposited  at  the  bottom  of  the 
vessel,  while  the  finer  passes  over  suspended  in  the  water. 
By  repeated  decantations  in  this  way,  deposits  are  obtained 
of  different  degrees  of  fineness ;  the  last,  or  that  which 
remains  longest  floating  through  the  liquid,  being  the 
finest.  The  resulting  powders  must  be  kept  in  separate 
bottles.  The  coarser  ashes  are  used  for  the  cupellation  of 
rich  silver  ores,  and  the  finer  for  assaying  ores  in  which 
only  a  minute  quantity  of  gold  or  silver  is  present. 

PBOOF  LEAD  is  made  use  of  in  cupelling  argentiferous  or 
auriferous  substances  ;  it  must  be  free  from  silver.  Dumas 
states  that  the  best  method  of  obtaining  lead  in  this  desir- 
able state  is  to  decompose  the  best  white-lead  by  means  of 
charcoal,  as  it  is  then  impossible  for  it  to  contain  any  other 
metal. 

TINFOIL  is  employed  to  reduce  certain  peroxides  to  the 
state  of  protoxide.  When  it  is  used,  a  small  roll,  about  a 
quarter  of  an  inch  long,  is  plunged  into  the  fused  button, 
and  heated  strongly  in  the  reducing  flame  :  the  desired 
.effect  is  then  produced. 

DRY  SILVER  CHLORIDE. — Herr  H.  Gericke  proposes  the 
employment  of  this  compound  in  qualitative  blowpipe 
.assays.  In  an  elaborate  paper  on  this  subject,  communi- 
cated to  the  '  Chemical  Gazette '  (vol.  xiii.  p.  189),  he  says : — 

'  Amongst  the  phenomena  which  characterise  different 
bodies  before  the  blowpipe,  and  serve  for  their  distinction, 
the  colour  of  the  flame  is  of  no  small  importance.  This 
power  of  colouring  the  blowpipe  flame  is  not,  however, 
exhibited  by  all  bodies  with  sufficient  intensity  to  enable 
them  to  be  distinguished  by  it  with  certainty ;  and  certain 
substances  are  consequently  usually  employed,  such  as 
muriatic  acid  with  baryta,  strontia  and  lime,  or  sulphuric 
.acid,  partly  to  form  and  partly  to  set  free  volatile  com- 


224  USE   OF   CHLORIDE   OF   SILVER. 

pounds.  By  this  means,  however,  although  the  intensity 
of  the  coloration  is  heightened,  its  duration  is  not  increased,, 
as  these  acids,  and  particularly  muriatic  acid,  evaporate  for 
the  most  part  before  they  have  acted  sufficiently,  so  that 
the  coloration  lasts  only  for  a  few  moments.  This  defect 
may  be  got  over  by  the  employment,  instead  of  the  volatile 
muriatic  acid,  of  a  chloride,  which  will  retain  the  chlorine 
at  a  high  temperature,  so  that  it  may  only  be  set  free  by 
degrees  in  small  quantities,  while  the  body  forming  its 
base  may  be  without  action  upon  the  colouring  power  of 
the  body  under  investigation.  For  this  purpose  chloride 
of  silver  appears  to  be  the  best,  especially  as  it  may  readily 
be  prepared  in  a  state  of  purity.  The  best  plan  is  to  stir 
it  with  water  into  a  thick  paste,  and  keep  it  in  a  bottle. 

'  In  regard  to  the  action  of  chloride  of  silver  upon  the 
coloration  of  the  blowpipe  flame,  I  have  investigated 
several  compounds  of  potash,  soda,  lithia,  lime,  baryta, 
strontia,  copper,  molybdenum,  arsenic,  antimony,  and  lead, 
and  mixtures  of  these  substances.  Chloride  of  silver,  of 
course,  has  no  action  upon  borates  and  phosphates,  both 
of  these  acids  being  amongst  those  which  offer  the  most 
resistance  to  the  action  of  heat. 

'  For  a  support,  I  employed  first  of  all  platinum  wire,, 
but  this  is  soon  alloyed  by  the  metallic  silver  which  sepa- 
rates, and  thus  rendered  useless  in  testing  metals.  Silver 
wire  is  too  readily  fusible,  and  also  difficult  to  obtain  free 
from  copper,  which  may  give  rise  to  errors  when  in  contact 
with  chloride  of  silver.  For  these  reasons,  iron  wire  is 
best  fitted  for  experiments  with  chloride  of  silver,  as  from 
its  cheapness  a  new  piece  may  be  employed  for  each  experi- 
ment, while  the  silver  may  readily  be  obtained  in  the  form 
of  chloride  from  the  broken  pieces.  If  the  size  of  the  frag- 
ment under  examination  be  sufficient,  the  platinum  forceps 
may  be  employed. 

'  The  results  at  which  I  arrived,  by  the  employment  of 
chloride  of  silver,  in  comparison  with  those  obtained  with- 
out this  reagent,  are  as  follows  : 

'  With  potash  compounds,  such  as  saltpetre,  potashes,, 
&c.,  the  flame  is  decidedly  of  a  darker  colour  with 


IN   BLOWPIPE   ASSAYS.  225 

chloride  of  silver  ;  and  even  in  ferrocyanide  of  potassium, 
which,  when  treated  by  itself  with  the  blowpipe,  colours 
the  flame  blue,  the  addition  of  chloride  of  silver  produces 
a  distinct  potash  coloration. 

6  The  action  of  chloride  of  silver  upon  soda  salts  is  not 
so  favourable  ;  for  although  with  some,  as  nitrate  of  soda, 
common  soda,  and  labradorite,  the  flame  acquires  a  more 
intense  yellow  colour  by  the  addition  of  chloride  of  silver, 
this  reagent  produces  no  observable  difference  with  other 
soda  compounds,  such  as  sulphate  of  soda  and  analcime. 
This  also  applies  to  the  compounds  of  lithia,  some  of 
which  give  a  finer  purple-red  colour  on  the  addition  of 
chloride  of  silver,  whilst  upon  others  it  has  no  such  effect 

'  With  lime  compounds  chloride  of  silver  acts  favour- 
ably upon  the  colouring  power.  Thus  the  addition  of 
chloride  of  silver  to  calcareous  spar  or  gypsum  (in  the 
reduction  flame)  gives  the  flame  a  more  distinct  yellowish- 
red  colour,  but  stilbite  gives  no  coloration  either  with  or 
without  chloride  of  silver.  With  fluor-spar  the  coloration 
cannot  well  be  observed,  as  this  decrepitates  too  violently 
under  the  blowpipe. 

'  The  action  of  chloride  of  silver  upon  compounds  of 
baryta  and  strontia  is  decidedly  advantageous,  as  both  the 
intensity  of  the  coloration  and  its  duration  leave  nothing 
to  be  desired.  Siliceous  celestine,  which,  when  heated  by 
itself  in  the  forceps,  scarcely  coloured  the  flame,  immedi- 
ately produced  a  permanent  red  coloration  when  heated 
with  chloride  of  silver. 

'Although  it  appears  from  the  preceding  statements, 
that  the  employment  of  chloride  of  silver  presents  no 
advantage  with  some  substances,  it  may  be  used  with 
good  results  in  the  treatment  of  mixtures  of  alkalies  and 
earths. 

'  Thus,  with  petalite  alone  the  lithia  coloration  is  first 
produced,  and  a  slight  soda  coloration  is  afterwards 
obtained  ;  whilst  with  chloride  of  silver  the  soda  coloration 
appears  very  distinctly  after  that  of  the  lithia.  With 
lithion-mica  alone  a  very  distinct  lithia  coloration  is 
presented  ;  but  in  the  presence  of  chloride  of  silver  a 

Q 


226  USE    OF   CHLORIDE    OF   SILVER 

colour  is  first  produced  which  may  lead  to  the  conclusion 
that  potash  is  present,  but  the  lithia  coloration  is  weak- 
ened. Ryacolite,  heated  by  itself  in  the  blowpipe  flame, 
only  gives  a  distinct  soda  coloration  ;  but  with  chloride  of 
silver  a  slight  potash  coloration  is  first  produced,  and  the 
colour  of  soda  then  appears  very  distinctly  ;  the  lime 
contained  in  it  cannot,  however,  be  detected  by  the  colora- 
tion of  the  flame. 

'  Chloride  of  silver  may  be  employed  with  still  greater 
advantage  with  the  following  metals,  but  in  these  cases  it 
is  particularly  necessary  that  the  operator  should  become 
familiar  with  the  colour  produced  by  each  individual 
substance. 

*  With  copper  compounds,  such  as  red  copper  ore, 
malachite,  copper  pyrites,  sulphate  of  copper,  &c.,  when 
contained  in  other  minerals  so  as  to  be  unrecognisable  by 
the  eye,  the  employment  of  chloride  of  silver  may  be  of 
the  greatest  service,  as  the  smallest  quantities  of  copper, 
when  treated  with  chloride  of  silver  under  the  blowpipe, 
give  a  continuous  and  beautiful  blue  colour  to  the  flame. 
With  chloride  of  silver  the  presence  of  copper  may  be 
distinctly  ascertained  by  the  blowpipe,  even  in  a  solution 
which  is  no  longer  coloured  blue  by  the  addition  of 
ammonia. 

'  The  employment  of  chloride  of  silver  will  be  equally 
advantageous  with  molybdenum,  as  in  this  case  also  the 
flame  gains  greatly  in  intensity.  Arsenic,  lead,  and  anti- 
mony are  already  sufficiently  characterised,  the  former  by 
its  odour,  the  two  latter  by  their  fumes  ;  but  even  with 
these  metals  chloride  of  silver  may  be  employed  with  ad- 
vantage to  render  their  reactions  still  more  distinct.  It  is 
only  necessary  to  observe,  that  the  greenish-blue  flame  of 
antimony  appears  greener  and  more  like  that  of  molyb- 
denum under  the  influence  of  chloride  of  silver. 

4  Chloride  of  silver  may  also  be  employed  with  com- 
pounds containing  several  of  the  above-mentioned  metals. 

6  If  bournonite  be  heated  in  the  oxidation  flame  of  the 
blowpipe,  a  fine  blue  flame  is  first  produced,  which  in- 
dicates lead  with  certainty  ;  if  chloride  of  silver  be  now 


IN   BLOWPIPE  ASSAYS.  227 

applied,  copper  is  also  readily  shown.  The  antimony 
contained  in  bournonite  cannot  be  ascertained  by  the 
coloration  of  the  flame ;  but  this  may  easily  be  detected 
upon  charcoal,  or  in  a  glass  tube  open  at  both  ends. 

'  Native  molybdate  of  lead,  without  chloride  of  silver, 
only  gives  a  blue  colour  to  the  blowpipe  flame  ;  with 
chloride  of  silver  this  blue  coloration  of  the  lead  comes 
out  more  distinctly,  but  at  the  same  time  the  tip  of  the 
flame,  particularly  when  the  reduction  flame  is  employed, 
appears  of  a  beautiful  yellowish-green  colour  from  molyb- 
denum. 

*  With  mixtures  of  arsenic  and  copper,  or  antimony 
and  copper,  the  flame  first  acquires  a  greyish-blue  or 
greenish-blue  colour  from  the  oxidation  of  the  arsenic  or 
antimony  ;  the  copper  may  then  be  very  easily  detected  by 
chloride  of  silver.  This  applies  also  to  mixtures  of 
arsenic  and  molybdenum,  or  antimony  and  molybdenum ; 
with  chloride  of  silver  the  yellowish-green  flame  of 
molybdenum  appears  distinctly.  It  will  be  more  difficult 
to  analyse  mixtures  of  arsenic  and  lead,  or  antimony  and 
lead,  in  this  manner  ;  and  if  a  compound  contain  both 
arsenic  and  antimony,  these  two  bodies  are  not  to  be 
distinguished  with  chloride  of  silver  under  the  blowpipe. 

'  From  these  experiments  it  appears  that  in  blowpipe 
testing  it  is  advantageous  to  employ  chloride  of  silver 
instead  of  muriatic  acid. 

4  Chloride  of  silver  is  particularly  to  be  recommended 
in  testing  metallic  alloys  for  copper.  Thus,  to  test  silver 
for  copper,  chloride  of  silver  may  be  applied  to  the  ends 
of  silver  wires,  and  on  the  application  of  heat  the  smallest 
quantity  of  copper  will  furnish  the  most  distinct  reaction. 
This  is  as  sensitive  as  any  of  the  known  copper  reactions, 
and  may  be  performed  quickly  and  easily.  In  testing 
metallic  alloys  for  traces  of  copper,  it  may  be  advisable  to 
submit  those  which  contain  antimony,  zinc,  lead,  and  other 
volatile  metals  to  roasting,  so  as  to  drive  off  these  metals 
before  the  addition  of  chloride  of  silver.' 

SODA-PAPER. — Mr.  Forbes  writes  as  follows  in  the 
*  Chemical  News ' :  '  As  it  would  be  impossible  to  submit  any 

Q  2 


228 


SODA    PAPER. 


FIG.  74. 


powdered  substance  to  the  direct  action  of  the  blowpipe 
flame  without  its  suffering  mechanical  loss,  some  means 
must  be  employed  for  holding  the  particles  together  until 
they  are  so  agglutinated  by  the  heat  that  no  such  loss 
need  be  apprehended ;  this  is  secured  by  the  use  of  the 
soda-paper  envelope  or  cornet,  as  devised  by  Harkort. 
For  this  purpose  slips  of  thin  slightly  sized  writing  paper,, 
about  1J  inch  long  by  1  inch  broad,  are  steeped  in  a 

solution  of  one  part  crystal- 
lised pure  carbonate  of  soda 
(free  from  sulphate)  in  two 
parts  of  water.  When  dried 
these  are  used  for  forming 
small  cylindrical  cornets,  by 
rolling  them  round  the  ivory 
cylinder,  fig.  74  d,  previously 
described.  A  bottom  is  formed 
to  them  by  folding  down  a 
portion  of  their  length  on  to 
,  the  end  of  the  cylinder,  which 
(f  is  then  pressed  firmly  into  the 
corresponding  mould  in  the 
blowpipe  anvil,  and  which,  upon  the  withdrawal  of  the 
cylinder,  serves  as  a  support  until  they  are  filled  with  the 
assay  from  the  scoop  in  which  the  assay  and  flux  have 
been  mixed.  After  pressing  the  assay  down,  the  super- 
fluous paper  is  cut  off,  leaving  only  sufficient  when  folded 
down  upon  the  contents  of  the  cornet,  to  form  a  paper 
cover  to  the  top  similar  to  the  hollow  of  the  cornet.  The 
assay  is  then  ready  for  placing  in  a  bore  in  the  charcoal, 
formed  by  the  charcoal  borer  c,  fig.  72,  and  is  then 
submitted  to  a  reducing  fusion.' 


GENERAL    ROUTINE    OF    BLOWPIPE    OPERATIONS. 

Size  of  the  Assay. — The  morsel  operated  on  is  suffi- 
ciently large  when  the  effect  of  the  heat  and  the  fluxes  added 
can  be  distinctly  discerned.  The  size  of  the  assay-piece 
generally  recommended  is  much  too  large  ;  its  size  ought 


OPERATIONS   IN   BLOWPIPE    ANALYSIS.  229 

to  be  about  that  of  a  mustard-seed  ;  that  of  the  flux  added, 
about  the  size  of  a  hemp-seed.  It  should  in  general  be 
previously  reduced  to  fine  powder. 

When  a  large  piece  is  employed,  the  experiment  con- 
sumes much  more  time  and  requires  much  more  labour 
than  a  smaller  piece.  It  is  only  in  reductions  that  a 
larger  piece  may  be  successfully  employed,  because  in 
that  case  the  more  metal  produced,  the  more  readily  can 
its  nature  be  ascertained.  Having  thus  endeavoured  to 
fix  the  size  of  the  assay,  we  will  now  lead  our  readers  to 
the  operations  necessary  in  blowpipe  analysis,  and  in  the 
order  in  which  they  are  to  be  performed. 

First. — The  substance  is  heated  in  the  closed  tube,  or 
mattrass,  over  a  spirit  lamp.  It  may,  by  this  treatment, 
decrepitate,  or  give  off  water,  or  some  other  volatile  sub- 
stance. 

Secondly. — It  is  heated  gently  on  charcoal,  by  aid  of 
the  blowpipe ;  and,  as  soon  as  warm,  withdrawn  from  the 
heat,  and  the  odour  given  off  ascertained  :  volatile  acids, 
arsenic,  selenium,  or  sulphur,  may  be  present.  The  odour 
thus  produced  by  the  oxidising  flame  must  be  compared 
with  that  produced  by  the  reducing  flame ;  if  there  is  any 
difference,  it  must  be  carefully  noted.  Sulphur,  selenium, 
&c.,  are  best  detected  in  the  oxidising  flame,  and  arsenic 
in  the  reducing  flame. 

Thirdly. — The  substance  is  examined  as  regards  its 
fusibility.  If  it  be  in  grains,  it  is  better  acted  upon  on 
charcoal,  notwithstanding  its  liability  to  escape  on  the  first 
insufflation,  when  not  very  fusible.  But  if  we  can  choose 
the  form,  it  is  better  to  knock  off  a  small  splinter,  by  means 
of  the  hammer,  and  hold  it  in  the  flame  by  the  platinum- 
pointed  pincers.  A  fragment  with  the  most  pointed  and 
the  thinnest  edges  ought  to  be  selected.  By  thus  acting, 
we  can  always  ascertain  at  a  glance  if  the  substance  be 
fusible  or  not.  Infusible  substances  retain  their  sharp 
points  and  angles,  which  can  be  ascertained  immediately  by 
means  of  a  microscope.  The  points  are  merely  rounded  in 
bodies  of  difficult  fusibility,  and  in  substances  of  easy 
fusion  are  rendered  globular. 


230  PRELIMINARY   BLOWPIPE    OPERATIONS. 

Certain  substances,  and  particularly  some  minerals, 
change  both  aspect  and  form  when  exposed  to  the 
blowpipe  flame,  without  entering  into  fusion  ;  some  swell 
up  like  borax ;  some  of  them  fuse  after  tumefaction  ; 
others  keep  in  that  state  without  fusion.  Some  minerals 
give  off  a  sort  of  foam  on  fusing,  giving  rise  to  a  kind  of 
blebby  glass,  which,  although  transparent  itself,  does  not 
appear  so,  on  account  of  the  multitude  of  air-bubbles  it 
contains. 

This  bubbling  and  tumefaction  takes  place  in  the 
greater  part  of  the  minerals  only  at  that  temperature  at 
which  all  the  water  is  disengaged  ;  and  these  ramifications 
appear  to  proceed  from  a  new  molecular  arrangement, 
produced  by  the  action  of  heat  on  the  constituent  parts  of 
the  substance.  It  cannot  be  said  that  the  expansion  of  a 
particular  part  of  the  substance  or  its  formation  into  gas, 
gives  rise  to  this,  because  it  most  often  happens  in  those 
substances  which  contain  no  such  substance.  The 
minerals  which  generally  give  these  indications  are  the 
double  silicates  of  lime  or  alkali,  and  alumina.  It  some- 
times disappears  after  a  few  instants,  and  occasionally 
lasts  as  long  as  the  substance  is  kept  in  fusion.  In  the 
latter  case,  it  seems  that  the  assay  takes  carbonic  acid 
from  the  flame,  which  carbonic  acid  is  transformed  by  the 
charcoal  into  carbonic  oxide,  and  it  is  that  gas  which 
causes  the  bubbles. 

In  the  employment  of  fluxes,  it  is  necessary  to  continue 
the  blast  for  a  sufficiently  long  time,  because  some  sub: 
stances  appear  infusible  at  the  commencement  of  the  oper- 
ation, and  gradually  yield  to  the  influence  of  the  flux,  and 
in  about  two  minutes  enter  into  full  fusion.  The  substance 
is  best  added  in  small  quantities,  and  no  new  dose  must  be 
introduced  until  the  former  one  is  acted  upon,  so  that  at 
last  the  glass  arrives  at  that  degree  of  saturation  that  it  can 
dissolve  no  more  :  it  is  at  this  particular  point  that  the 
reactions  are  most  vivid  and  plain.  Beads  of  glass,  not  so 
saturated,  do  not  give  such  decided  indications. 

Occasionally,  in  operating  with  a  flux  in  the  reducing 
flame,  it  happens  that  the  assay-bead  reoxidises  during  the 


DISCRIMINATION   OF   MINERALS   BEFORE   THE   BLOWPIPE.      231 

cooling  of  the  charcoal,  and  thus  the  labour  of  a  preceding- 
operation  is  lost.  In  order  to  obviate  this  inconvenience, 
the  charcoal  is  turned  over,  so  that  the  bead  may  fall  in  a 
yet  liquid  state  on  some  cold  body,  as  a  porcelain  plate. 

When  the  colour  of  the  bead  is  so  intense  that  it  appears 
opaque,  its  transparency  can  be  proved  by  holding  it 
opposite  to  the  flame  of  a  lamp ;  the  reversed  image  of 
the  flame  can  then  be  seen  in  the  bead,  tinged  with  the 
colour  imparted  to  the  flux  by  the  body  under  experiment. 
The  globule  may  also  be  flattened  by  a  pair  of  pliers  before 
it  cools,  or  it  may  be  drawn  into  a  thin  thread.  In  either 
of  the  last-mentioned  cases  its  colour  can  readily  be  ascer- 
tained. 

Minerals  exposed  to  the  exterior  and  interior  flame, 
either  with  or  without  fluxes,  present  a  variety  of 
phenomena,  which  ought  to  be  carefully  noted,  and  which, 
collectively,  form  the  result  of  the  assay.  The  smallest 
circumstance  must  not  be  overlooked,  because  it  may  lead 
us  to  ascertain  the  presence  of  a  substance  not  suspected. 
It  is  necessary,  in  all  cases,  to  make  two  assays,  and 
compare  the  separate  results  ;  because  it  sometimes  happens 
that  an  apparently  trivial  fact  had  been  overlooked  in  the 
first  series  of  operations,  which  materially  conduces  to  the 
good  result  of  the  experiment. 


DISCRIMINATION   OF   MINERALS.* 

Selecting  those  minerals  which  are  remarkable  for 
their  wide  distribution,  and  at  the  same  time  those  which 
are  of  value,  whether  rare  or  frequent,  the  number  which 
it  is  advisable  for  the  explorer  to  know  is  reduced  to  about 
seventy-five,  and  it  is  only  to  this  limited  number  that 
reference  will  be  made  in  this  chapter. 

*  This  method  of  distinguishing  the  various  minerals,  ores,  etc.  which  are 
likely  to  be  met  with  during  an  exploration,  is  partly  condensed  from  a  very 
valuable  pamphlet  by  Alexander  M.  Thompson,  D.Sc.,  Professor  of  Geology  at 
the  University  of  Sydney,  entitled  *  Guide  to  Mineral  Explorers  in  Distinguishing- 
Minerals,  Ores,  and  Gems.'  The  instructions  given  will  not  be  found  to  involve 
greater  difficulties  than  can  be  overcome  by  a  little  practice  and  perseverance. 
The  appliances  which  are  needed  may  be  bought  for  a  few  shillings,  and  will  be 
found  too  trifling  in  weight  and  bulk  to  incommode  the  traveller. 


232 


DISCRIMINATION    OF    MINERALS. 


The  distinctions  in  minerals  lie  in  their  chemical  and 
physical  characters  ;  but  as  the  appearance  of  a  mineral 
may  afford  little  or  no  indication  of  what  these  are,  they 
have  to  be  discovered  by  testing. 

>-v  These  characters  will  be  described  in  detail,  and  the 
modes  of  testing  will  be  indicated,  where  necessary. 

The  characters  include  crystalline  form,  mode  of 
fracture,  colour,  lustre,  transparency,  taste,  odour,  feel, 
hardness,  specific  gravity,  fusibility,  and  chemical  com- 
position. 

Crystalline  Form. 

The  crystalline  form  is  an  important  guide  in  many 
cases,  but  crystals  are  subject  to  so  many  modifications, 


FIG.  75. 


FIG.  76. 


FIG.  77. 


FIG.  78. 


FIG.  81. 


FIG.  80. 


FIG.  82. 


that  this  character  ceases  to  be  a  practical  one  except  to 
those  persons  who  are  familiar  with  its  geometrical  laws. 


DISCRIMINATION   OF   MINERALS.  233 

Still  it  is  very  useful  to  know  a  few  common  primary 
forms  such  as  the  following  : — 

CUBE. — 6  sides  or  faces,  each  square  (fig.  75). 

OCTAHEDRON. — 8  sides,  each  an  equal-sided  triangle 
<fig.  76). 

DODECAHEDRON. — 12  sides,  each  rhombic, — (shaped  like 
the  diamond  of  a  pack  of  cards)  (fig.  77). 

TETRAHEDRON. — 4  sides,  each  triangular  (fig.  78). 

EHOMBOHEDRON. — 6  sides,  each  rhombic  (fig.  79). 

PRISM. — Any  column  with  three  or  more  sides  ;  when 
placed  on  its  base,  it  may  stand  straight  or  oblique ;  it  may 
terminate  abruptly  with  a  flat  face,  or  come  off  to  a  point, 
blunt  or  sharp,  like  a  pyramid  (figs.  80,  81,  82). 


Mode  of  Fracture. 

The  mode  in  which  a  mineral  breaks  when  smartly 
.struck  with  a  hammer,  or  pressed  with  the  point  of  a  knife, 
is  a  character  of  importance.  Many  can  only  be  broken 
in  certain  directions  ;  for  instance,  a  crystal  of  calc-spar 
can  only  be  split  parallel  to  the  faces  of  a  rhombohedron ; 
many  crystals  break  more  easily  in  one  direction  than  in 
others.  Whenever  a  mineral  breaks  with  a  smooth,  flat, 
even  surface,  it  is  said  to  exhibit  cleavage.  Cleavage 
always  depends  upon  the  crystalline  form.  But  minerals 
often  break  in  irregular  directions,  having  no  connection 
whatever  with  the  crystalline  form,  and  this  kind  of 
breaking  is  called  fracture ;  the  broken  surfaces  are  usually 
irregular  or  conchoidal  (i.e.  with  concave  and  convex  out- 
lines, like  shells). 

Lustre. 

Some  minerals  have  a  brilliant  lustre  like  that  of  metals ; 
in  others  the  lustre  resembles  that  of  glass,  silk,  resin, 
or  wax  ;  while  others  are  dull,  or  destitute  of  lustre.  The 
lustre  of  the  diamond  is  called  adamantine. 


234  DISCRIMINATION   OF    MINERALS. 


Colour  and  Streak. 

Minerals  may  be  colourless,  white,  black,  or  of  any 
colour,  either  dull  or  brilliant.  The  same  mineral  may 
present  a  variety  of  similar  tints,  or  even  distinct  colours. 
It  often  happens  that  a  mineral,  which  when  viewed  in  a 
solid  mass  possesses  a  distinct  colour,  affords  a  powder 
which  has  a  colour  different  from  that  of  the  solid  mass, 
or  is  even  destitute  of  colour,  that  is  to  say,  white  or 
nearly  so.  The  dust  formed  on  scratching  a  mineral  with 
a  knife,  or  by  a  splinter  of  quartz,  or  by  a  diamond,  is 
termed  the  '  streak ' :  it  has  usually  the  same  colour  as  the 
powder.  The  colour  of  a  mineral  and  its  streak  may  cor- 
respond ;  or  the  mineral  and  its  streak  may  possess  diffe- 
rent colours  ;  or  the  mineral  may  be  coloured,  while  its 
streak  is  colourless. 

For  instance,  cinnabar  has  both  a  red  colour  and  a  red 
streak. 

Specular  iron  has  a  black  colour,  but  a  red  streak. 

Sapphire  has  a  blue  colour,  but  a  white  or  colourless 
streak. 

The  streak  of  most  minerals  is  dull  and  pulverulent,  but 
a  few  minerals  exhibit  a  shining  streak,  like  that  formed  on 
scratching  a  piece  of  lead  or  copper.  This  kind  of  streak 
is  distinguished  by  the  name  of  Metallic. 

In  judging  the  colour  of  a  mineral  a  surface  quite  free 
from  tarnish  should  be  chosen. 

The  colour  of  a  transparent  gem  can  be  seen  to  best 
advantage  by  immersing  it  in  water,  about  half  an  inch 
below  the  surface. 

Hardness. 

This  character  is  of  great  importance  in  distinguishing 
minerals ;  it  implies  the  degree  of  facility  with  which  the 
particles  may  be  separated  by  cutting  or  scratching.  The 
diamond  is  the  hardest  substance  known,  as  it  will  scratch 
all  others.  Talc  is  one  of  the  softest  minerals.  Other 
minerals  possess  intermediate  degrees  of  hardness.  To 
express  how  hard  any  mineral  is,  it  becomes  necessary  to 


DISCRIMINATION   OF   MINERALS.  235 

compare  it  with  some  known  standard.  Ten  standards  of 
different  degrees  have  been  chosen,  and  are  given  in  order 
in  the  following  scale  : — 

1.  Talc.  6.  Felspar. 

2.  Gypsum.  7.  Quartz. 

3.  CalcSpar.  8.  Topaz. 

4.  Fluor  Spar.  9.  Corundum,  or  Sapphire, 

5.  Apatite.  10.  Diamond. 

The  hardness  of  a  mineral  may  often  be  found  by 
drawing  the  point  of  a  steel  knife  across  it.  For  instance, 
the  slightest  pressure  ^frill  suffice  to  scratch  talc  ;  fluor-spar 
is  not  so  easily  scratched  as  calcite  ;  the  greatest  pressure 
is  needed  to  scratch  felspar  ;  and  quartz  does  not  yield  to 
the  knife  at  all. 

The  hardness  may  also  be  found  by  scratching  one 
mineral  with  another ;  thus,  the  diamond  will  scratch  all 
other  minerals  ;  corundum  scratches  topaz,  topaz  scratches 
quartz,  quartz  scratches  felspar  ;  and  so  on. 

If  on  drawing  a  knife  across  a  mineral  it  is  impressed 
as  easily  as  calcite,  its  hardness  is  said  to  be  3.  If  a 
mineral  scratches  quartz,  but  is  itself  scratched  by  topaz, 
its  hardness  is  between  7  and  8. 

In  trying  the  hardness  of  a  mineral  a  little  judgment 
is  necessary  ;  for  instance,  a  sound  portion  of  the  mineral 
must  be  chosen ;  a  sharp  angle  used  in  trying  to  scratch : 
a  streak  of  dust  on  scratching  one  mineral  with  another 
may  come  from  the  waste  of  either,  and  it  cannot  be  de- 
termined which  is  the  softer,  until  after  wiping  off  the  dust, 
and  viewing  with  a  lens. 

The  use  of  the  above  scale,  however,  implies  an  ac- 
quaintance with  the  ten  standard  minerals.  It  is  very 
desirable  to  have  specimens  of  these  minerals  for  reference. 
But  a  collection  of  the  following  common  minerals,  which 
can  easily  be  procured,  will  be  found  quite  enough  for 
ordinary  purposes,  viz.  :  calc-spar,  felspar,  quartz,  topaz 
(white  or  yellow),  and  corundum  or  sapphire. 

By  the  test  of  hardness  clear  distinctions  may  be  drawn 
between  minerals  which  resemble  each  other  ;  for  instance, 


236  DISCRIMINATION   OP   MINERALS. 

iron  pyrites  and  copper  pyrites  are  similar  in  appearance, 
but  copper  pyrites  can  easily  be  scratched  with  a  knife, 
whereas  iron  pyrites  is  nearly  as  hard  as  quartz  and  cannot 
be  impressed  with  a  knife  at  all. 

In  determining  the  hardness  of  small  stones,  it  is  most 
convenient  to  fasten  them  by  heating  upon  a  stick  of  seal- 
ing wax. 

Specific  Gravity. 

By  specific  gravity  is  meant  the  comparative  weight  of 
equal  bulks.  Water  is  taken  as  the  standard  of  compari- 
son ;  the  specific  gravity  of  a  mineral  is  a  number  showing 
how  many  times  it  is,  bulk  for  bulk,  heavier  than  water. 

The  specific  gravity  of  water  is  called  1,  of  gold  19, 
implying  that,  if  equal  bulks  of  gold  and  water  were  taken, 
the  gold  would  weigh  19  times  as  heavy  as  the  water.  The 
specific  gravity  of  a  mineral  can  be  found  by  weighing  it 
first  in  air  in  the  usual  manner,  and  then  observing  how 
much  of  its  weight  it  loses,  when  suspended  from  the  arm 
or  pan  of  a  balance,  and  allowed  to  hang  freely  in  water. 
If  a  piece  of  quartz  weighing  26  grains  is  attached  by  a 
hair  or  thin  cotton  to  the  scales,  and  weighed  whilst  hang- 
ing in  water,  it  will  be  found  to  weigh  only  16  grains  ;  it 
thus  loses  10  grains,  or  ^  of  its  entire  weight.  Similarly 
gold  would  lose  -^  of  its  weight. 

Minerals  differ  very  widely  in  the  proportion  of  weight 
which  they  lose  in  water,  but  the  same  mineral  invariably 
loses  the  same  proportion,  for  instance : 

Quartz  loses  ^  of  its  weight ;  topaz  ^  ;  sapphire  ^  ; 
zircon  if  ;  tin  ore  ±%. 

These  proportions  depend  upon  the  specific  gravity  of 
these  minerals.  The  specific  gravity  of  water  is  called  1, 
of  quartz  2-6,  of  topaz  3*5,  of  sapphire  4-0,  of  gold  19. 

In  determining  how  much  weight  a  mineral  loses  in 
water,  a  very  delicate  balance  is  required  when  the  weight 
in  air  is  under  10  grains  ;  but  for  portions  weighing  heavier 
than  this,  a  common  balance  turning  readily  to  a  grain, 
may  be  used  for  practical  purposes.  The  mineral  must  be 
sound  throughout,  and  free  from  any  pores  or  cracks,  and 


DISCRIMINATION   OF   MINERALS.  237 

its  surface  should  be  rubbed  over  with  water,  before  im- 
mersing it,  to  prevent  bubbles  of  air  adhering,  which  would 
falsify  the  result.  In  careful  trials  distilled  or  rain  water 
should  be  used.  A  trial  of  specific  gravity  can  have  no- 
value,  unless  it  is  made  on  a  pure  portion  of  a  mineral,  quite 
free  from  any  adhering  foreign  matter. 

A  rough  estimate  of  specific  gravity  can  be  formed  from 
the  feeling  of  pressure  in  shaking  any  mass  loosely  in  the 
palm  of  the  hand  ;  in  this  way  it  can  be  judged  whether 
the  specific  gravity  is  high  or  low. 

EULE. — The  rule  for  finding  the  specific  gravity  is  to 
divide  the  weight  of  the  mineral  in  air  by  its  loss  of  weight 
in  water.  Example  :  A  piece  of  quartz  weighed  1,398 
grains  in  air,  and  862  grains  in  water  ;  here  the  loss  of 
weight  is  536,  and  the  weight  in  air  divided  by  this  number 
is  2*6,  which  is  the  specific  gravity  of  quartz. 

For  separating  from  each  other  minerals  of  different 
specific  gravities  B.  Breon  proposes  the  use  of  melted  mix- 
tures of  lead  and  zinc  chlorides  in  different -proportions,  so 
as  to  yield  liquids  ranging  from  2 -4  to  5*0  in  specific 
gravity. 

Sonstadt*  has  devised  a  very  ingenious  and  useful 
method  of  taking  specific  gravities  of  minerals,  when  a 
rough  and  ready  method  of  discriminating  between  bodies 
of  similar  appearance  but  of  different  specific  gravities  is 
all  that  is  needed.  He  takes  a  solution  of  potassium 
iodide  saturated  at  the  common  temperature,  and  dissolves 
in  it  as  much  iodide  of  mercury  as  possible.  It  will 
then  dissolve  more  potassium  iodide,  then  more  mercuric 
iodide,  and  so  forth.  The  iodides  dissolve  very  slowly  at 
the  last,  and  as  it  is  best  not  to  accelerate  the  solution  by 
the  application  of  heat,  considerable  time  must  be  allowed 
when  a  liquid  of  maximum  strength  is  required.  The 
solution,  after  filtering,  is  fit  for  use,  and  it  may  be  ob- 
tained without  danger  of  its  crystallising  above  zero,  of 
sp.  gr.  3-085  at  12°  C.  This  liquid  is  transparent,  very 
mobile,  filters  easily,  is  of  an  amber  colour,  gives  no  precipi- 
tate on  addition  of  water,  and  does  not  readily  lose  or  gain 

*  <  Chemical  News,'  March  20,  1874,  vol.  ixix.  p.  127. 


238  .DISCRIMINATION    OF   MINERALS. 

water  on  long  exposure  to  the  atmosphere.  The  solution 
undergoes  no  perceptible  chemical  change  by  free  exposure 
to  the  air  for  many  months.  It  may  be  diluted  to  any 
•extent,  and  then  concentrated  by  heat  without  injury. 

When  this  liquid  is  diluted  so  that  quartz  will  just 
float  in  it,  any  mineral  heavier  than  quartz  will  of  course 
sink.  As  many  minerals  closely  resemble  quartz  in  external 
characters,  and  can  be  distinguished  more  readily  by  their 
specific  gravity  than  in  any  other  way,  this  method  of 
testing  the  specific  gravity  furnishes  a  very  quick  and 
certain  means  of  discrimination.  A  small  bottle  of  the 
liquid,  containing  say  half  an  ounce,  and  carried  in  the 
waistcoat  pocket,  will  enable  the  mineralogist  to  make  a 
great  many  examinations  in  his  walks  as  to  whether  the 
specimens  examined  are  above  or  below  a  certain  specific 
gravity.  The  smallest  distinctly  visible  particle  of  a 
mineral  is  enough  for  a  determination.  After  the  bottle 
becomes  clogged  with  specimens,  the  liquid  may  be  poured 
out  for  further  -use,  and  if  the  washings  are  added  and  the 
whole  concentrated  there  need  be  no  sensible  waste. 

Mr.  Hardman  suggests  that  with  this  liquid  it  would 
be  possible  to  separate  completely  the  three  constituent 
minerals  of  granite — mica,  felspar,  and  quartz — weigh 
them,  and  determine  absolutely  their  percentage. 

Professor  Church  has  used  Sonstadt's  solution  exten- 
sively for  years  in  the  separation  of  rare  minerals  from 
their  siliceous  gangue.  He  says  he  has  often  identified 
the  minerals  of  a  crushed  fragment  of  rock  by  introducing 
a  drop  of  the  solution  into  the  '  live  box '  under  the 
microscope.  By  using  solutions  of  increasing  strength,  or 
adding  the  solid  salt,  the  felspars,  the  quartz,  and  then 
some  of  the  heavier  minerals  may  be  successively  brought 
to  the  surface  and  thus  into  focus. 


Fusibility. 

Some  minerals  can  be  easily  fused  ;  others  only  with 
difficulty,  while  others  resist  the  highest  heat  which  can 
be  applied  to  them.  There  are  such  wide  differences 


DISCRIMINATION    OF    MINERALS.  239 

Between  the  various  degrees  of  fusibility  of  minerals,  that 
this  character  helps  greatly  in  distinguishing  them.  The 
fusibility  is  most  readily  tested  by  holding  a  small  splinter 
of  the  mineral  with  a  forceps  in  a  candle  flame,  urged 
by  the  blowpipe  ;  or  the  mineral  maybe  laid  upon  a  piece 
of  charcoal,  and  the  flame  directed  upon  it  by  the  blow- 
pipe. Some  minerals  fly  to  pieces  when  heated,  others 
swell  up,  or  give  off  peculiar  and  characteristic  odours. 

Chemical  Characters. 

The  chemical  composition  of  a  mineral  is  one  of  the 
most  important  facts  to  know  respecting  it ;  the  various 
processes  for  determining  this  form  a  science  by  them- 
selves ;  but  only  the  tests  depending  upon  the  use  of  the 
blowpipe  will  be  described  here.  A  great  deal  can  be 
learnt  respecting  a  mineral  by  a  few  simple  trials  with  the 
blowpipe.  The  only  requirements  are  a  common  blow- 
pipe, a  candle,  a  forceps  or  pliers,  a  piece  of  No.  7  plati- 
num wire,  two  inches  long,  dried  sodium  carbonate,  dried 
borax,  and  potassium  cyanide.  The  charcoal  selected  for 
these  experiments  should  be  free  from  cracks  and  openings. 
By  dry  sodium  carbonate  is  meant  not  merely  dry  to  the 
touch,  but  quite  free  from  water  ;  this  may  be  prepared 
from  recrystallised  common  washing  soda,  by  expelling 
the  water  which  it  contains  ;  the  washing  soda  is  put  in  a 
shallow  clean  iron  dish,  and  placed  over  a  clear  fire  until 
a  white  dry  powder  is  formed  ;  too  strong  a  heat  might 
fuse  the  dry  powder.  A  quarter  of  an  ounce  may  be  kept 
in  a  well- corked  bottle  or  tube  for  use.  Sodium  bicarbo- 
nate may  be  used  instead  without  previous  heating  ;  or  if 
the  bicarbonate  be  moderately  heated,  it  loses  weight,  and 
becomes  sodium  carbonate,  quite  free  from  water  like  the 
above. 

The  borax  is  to  be  dried  in  the  same  way ;  a  quarter 
of  an  ounce  will  be  enough  ;  it  is  convenient  to  keep  the 
platinum  wire  in  the  same  tube.  Unless  these  tubes  are 
well  corked  these  chemicals  reabsorb  moisture.  For  test- 
ing tin  ore  it  is  useful  to  have  a  little  potassium  cyanide 


240  DISCRIMINATION    OF    MINERALS. 

kept  in  a  bottle  with  the  cork  and  rim  well  covered  with 
melted  bees'-wax ;  it  would  otherwise  liquefy,  by  absorption 
of  moisture,  and  become  useless.  It  is  a  most  dangerous 
poison,  and  the  greatest  caution  must  be  observed  in  its 
use. 

Three  kinds  of  effect  can  be  produced  by  the  blowpipe  ; 
first,  it  can  be  used  as  a  source  of  heat  for  testing  fusibility ; 
secondly,  it  can  add  oxygen  to  a  mineral ;  thirdly,  it  can 
take  oxygen  away. 

The  three  principal  means  of  chemically  testing 
minerals  before  the  blowpipe  are  (1)  with  borax,  (2)  on 
charcoal,  usually  with  the  addition  of  sodium  carbonate ; 
(3)  by  holding  in  the  point  of  oxidation. 

EXPERIMENT  No.  1. — Many  metals  impart  a  colour  to- 
fused  borax,  by  which  their  presence  can  be  recognised. 
To  try  this  experiment  a  bead  of  fused  borax  must  first 
be  obtained  on  the  platinum  wire.  The  end  of  the  wire 
is  bent  into  a  loop  or  ring  about  the  twelfth  part  of  an 
inch  in  diameter.  The  wire  is  then  heated  in  the  blowpipe 
flame,  and  dipped  whilst  hot  into  the  borax ;  the  portion 
of  borax  that  adheres  is  then  fused  on  to  the  wire  in  the 
blowpipe  flame,  and  the  hot  wire  is  again  dipped  ;  this  is- 
repeated  until  the  loop  contains  a  glass-like  bead  of  fused 
borax.  If  the  bead  has  become  cloudy,  the  soot  causing 
this  may  be  burned  off  in  the  oxidising  point  of  the  flame. 
Having  thus  obtained  a  clear,  colourless,  transparent  bead, 
the  next  step  is  to  add  to  it  a  minute  portion  of  the  mineral 
which  is  to  be  tested.  By  touching  a  little  of  the  finely 
pulverised  mineral  with  the  borax  bead,  while  softened  by 
heat,  enough  will  adhere  to  the  bead  for  a  first  trial.  The 
bead  is  then  kept  at  a  white  heat  in  the  oxidising  point  of 
the  flame  for  a  few  seconds,  and  on  removal  its  colour  is 
noted,  both  whilst  hot  and  when  cold.  If  no  colour  is 
imparted  a  fresh  trial  may  be  made  with  a  larger  quantity 
of  the  powder  ;  but  if  the  bead  is  opaque  owing  to  the 
depth  of  colour,  as  is  often  the  case,  a  fresh  experiment 
must  be  made,  using  a  still  smaller  quantity  of  the  powder. 
The  colour  can  only  be  fairly  judged  in  a  perfectly  trans- 
parent bead.  If  no  colour  can  be  obtained  in  the  oxidising 


DISCRIMINATION   OF   MINERALS.  241 

flame,  further  experiment  with  the  borax  bead  is  needless ; 
but  if  a  colour  is  obtained,  it  is  then  advisable  to  try  the 
effect  of  the  reducing  flame  upon  the  same  bead.  The 
following  observations  and  inferences  may  result  from  this 
test : — 

Colour  of  Bead  in 
OXIDISING.  REDUCING.  Pretence  of 

Green  (hot) :  Blue  (cold).  Red.  COPPER. 

Blue  (hot  and  cold).  Blue.  COBALT. 

Amethyst.  Colourless.  MANGANESE. 

Green.  Green.  CHROMIUM. 

Red  or  Yellow  (hot).  )        TJ  **i    r« 

Yellow  or  colourless  (cold).  ^°iile  Green'  IRO*' 

Violet  (hot)  ;  Red-Brown  (cold).    Grey  and  Turbid,  NICKEL. 

difficult  to  ob- 
tain. 

This  mode  of  testing  may  often  be  used  to  prove  the 
presence  of  the  above-mentioned  metals. 

It  requires  some  practice  before  trustworthy  results 
can  be  obtained  in  reducing  ;  the  reduced  bead,  if  brought 
out  of  the  flame  at  a  white  heat  into  the  air,  may  at  once 
oxidise ;  but  this  may  be  prevented  by  placing  it  inside 
the  dark  inner  cone  of  an  ordinary  candle  flame,  and 
allowing  it  to  cool  partially  there. 

EXPERIMENT  No.  2. — The  mode  of  testing  with  sodium 
carbonate  on  charcoal  is  performed  as  follows  : — A  sound 
piece  of  charcoal  half  an  inch  square  is  chosen,  and  a  neat 
cavity  is  scooped  out  on  its  surface,  into  which  is  placed 
a  mixture  containing  the  pulverised  mineral  to  be  tested, 
with  three  or  four  parts  of  sodium  carbonate,  the  whole 
not  exceeding  the  bulk  of  a  pea  ;  after  lightly  pressing 
the  mixture  into  the  cavity,  the  blowpipe  flame  may  be 
cautiously  applied  to  it ;  and  afterwards,  when  the  mix- 
ture no  longer  shows  a  tendency  to  fly  off,  the  charcoal 
may  be  advanced  nearer  to  the  blowpipe,  and  finally  be 
kept  at  as  high  a  temperature  as  possible  in  the  reducing 
part  of  the  flame. 

In  testing  for  tin  ore,  a  piece  of  potassium  cyanide 
about  the  size  of  a  pea  may  be  placed  upon  the  mixture 
after  the  first  application  of  heat,  and  the  further  applica- 
tion of  heat  may  then  be  continued. 

R 


242  DISCRIMINATION   OF   MINERALS. 

This  treatment  is  designed  to  extract  metals  from 
minerals ;  it  favours  in  the  highest  degree  the  removal  of 
oxygen.  But  like  the  borax  test,  it  is  limited  in  its  appli- 
cation ;  it  can  only  be  used  to  detect  certain  metals.  The 
failure  of  the  test,  in  any  case,  must  not  be  looked  upon  as 
a  conclusive  proof  of  the  absence  of  the  particular  metal 
sought :  for  instance,  copper  can  be  easily  abstracted  from 
copper  carbonate  by  this  test,  but  not  from  copper  pyrites. 
Still  the  test  is  a  most  valuable  and  indispensable  one  to 
the  mineralogist. 

The  test  is  complete  when  the  metal  is  obtained  as 
a  globule,  in  the  cavity  of  the  charcoal ;  in  many  cases 
the  globule  will  be  found  surrounded  with  the  oxide 
of  the  metal,  forming  an  incrustation  on  the  charcoal ; 
and  the  colour  of  such  incrustation  should  be  carefully 
noted,  both  at  the  moment  of  removal  from  the  flame, 
and  after  cooling.  By  pressing  the  globule  between 
smooth  and  hard  surfaces,  it  can  be  determined  whether 
the  metal  is  flattened  out  (or  malleable),  or  crushed  to 
pieces  (brittle). 

The  following  observations  and  inferences  may  result 
from  this  test : — 

GLOBULE.                               INCRUSTATION.  Presence,  of 

Yellow  (malleable).  None.  GOLD. 

White          do.                      Do.  SILVER. 

Red              do.                      Do.  COPPER. 

White          do.  White.  TIN. 

Do.             do.  Red  (hot) ;  Yellow  (cold).  LEAD. 

Do.        ("brittle).                 Do.              do.  BISMUTH. 

None.  Yellow  (hot)  ;  White  (cold).     ZINC. 

White,  "brittle,  giving  off  White.  ANTIMONY. 
fumes  when  removed 
from  the  flame. 

EXPERIMENT  No.  3. — In  addition  to  these  substances 
there  are  others  which  occur  abundantly  in  minerals,  and 
which  may  be  recognised  by  the  blowpipe  with  the  greatest 
ease ;  for  instance,  sulphur  and  arsenic.  These  may  be 
discovered  by  heating  a  fragment  of  the  mineral,  supported 
on  a  piece  of  charcoal,  or  held  in  a  forceps,  in  the  oxidising 
point  of  the  flame,  and  noticing  the  odour  which  is  given 
off;  a  smell  of  burning  sulphur  indicates  that  the  mineral 


DISCRIMINATION   OF    MINERALS.  243 

contains  that  substance,  and  white  fumes  having  a  garlic 
odour  indicate  the  presence  of  arsenic. 

Mercury,  antimony,  and  other  substances  may  escape 
as  fumes  when  heated  in  this  manner. 

Requirements  for  Testing  Minerals. 

The  requirements  already  mentioned  are  blowpipe, 
candle,  forceps,  platinum  wire,  dried  borax,  dried  sodium 
carbonate,  potassium  cyanide,  charcoal ;  also  the  minerals 
for  comparisons  of  hardness,  namely,  calc-spar,  felspar, 
quartz,  topaz,  sapphire.  In  travelling  it  is  well  to  dis- 
pense with  the  grain  scales  and  weights  for  taking  specific 
gravities.  It  would  be  dangerous  to  attempt  to  travel 
with  nitric  acid.  It  addition  to  these  it  will  be  found 
useful  to  have  a  steel  pocket-knife,  one  blade  of  which 
should  be  kept  magnetized,  which  may  be  easily  done  by 
touching  it  occasionally  with  a  strong  magnet ;  a  small 
iron  spoon  for  heating  minerals,  such  as  cinnabar,  over  a 
candle  flame  ;  also  a  small  pocket  lens. 

DESCRIPTION  OF  MINERALS. 
QUARTZ  AND  THE  SILICATES. 

Perhaps  no  other  mineral  presents  such  a  great  variety 
of  forms  and  colours  as  quartz,  and  no  mineral  occurs  in 
greater  abundance.  When  pure  it  consists  of  silica  only, 
but  it  is  usually  contaminated  with  other  ingredients, 
principally  alumina,  iron,  and  clay.  The  impure  varieties 
of  quartz  compose  most  of  the  pebbles  and  sand  of  the  soil. 

Out  of  the  six  hundred  minerals  at  present  known,  at 
least  two  hundred  and  fifty  contain  silica  in  greater  or  less 
proportion,  and  are  hence  termed  silicates. 

Silicates  are  indispensable  in  the  manufacture  of  glass, 
porcelain,  earthenware,  and  for  other  purposes ;  but  they 
exist  in  such  profusion  that  their  economic  value  is  ex- 
ceedingly trifling.  The  great  majority  of  the  silicates  are 
purely  objects  of  scientific  interest ;  a  few  forms  of  silica 
are  esteemed  as  gems,  such  as  the  precious  opal,  and  some 

R    2 


244  DISCRIMINATION   OF    MINERALS. 

varieties  of  quartz,  the  topaz,  the  emerald,  the  zircon  or 
hyacinth,  the  garnet  and  carbuncle,  the  tourmaline,  and 
some  others.  Handsome  varieties  of  serpentine  are  often 
used  in  ornamental  stonework. 

1.    QUARTZ. 

Chemical  Composition. — Silica. 

Crystallized  in  six-sized  prisms,  terminated  by  pyramids. 
Sides  of  the  crystal  often  marked  across  with  fine  parallel 
lines.  Transparent  or  opaque.  Colourless,  or  of  various 
colours.  Glassy  lustre.  Fracture  irregular,  conchoidal, 
Specific  gravity,  2 -6.  Hardness,  7.  Cannot  be  scratched 
with  a  knife  ;  scratched  by  topaz,  zircon,  sapphire,  and 
diamond,  and  thus  easily  distinguished  from  these  gems. 
Quartz  scratches  glass  with  facility ;  felspar  and  many 
other  minerals  can  be  scratched  by  quartz.  The  irregular 
fracture,  the  fine  parallel  markings,  and  the  hardness  gene- 
rally suffice  to  distinguish  quartz. 

Infusible  in  the  blowpipe  flame. 

The  following  are  the  chief  varieties  of  quartz  ;  the 
differences  are  due  either  to  their  mode  of  formation  or 
the  presence  of  impurities.  They  have  the  same  general 
characters  as  pure  quartz. 

1.  TRANSPARENT  VARIETIES  : — 

EOCK  CRYSTAL. — Pure,  transparent,  colourless  quartz. 
Used  for  spectacle  glasses  and  ornaments. 

AMETHYST. — Transparent,  Of  a  rich  violet  or  purple 
.colour.  Used  as  a  gem. 

EOSE  QUARTZ. — Seldom  perfectly  transparent.  Of  a 
rosy  tint. 

CAIRNGORM,  or  SMOKY  QUARTZ,  is  transparent,  with  a 
smoky  tinge. 

FALSE  TOPAZ  has  a  yellow  pellucid  colour,  distinguished 
from  topaz  and  oriental  topaz  by  its  inferior  hardness. 

2.  SEMI- TRANSPARENT  VARIETIES  : 

CHALCEDONY. — Pale  colour  and  waxy  lustre.  Eesem- 
bling  icicles  in  some  instances,  the  frothy  surface  of  a 
liquid  in  others. 


DISCRIMINATION   OP   MINERALS.  245 

CARNELIAN  and  SARD  have  red  tints. 

AGATE  exhibits  cloudy  or  moss-like  patches,  or  a 
number  of  lines  arranged  in  circular  and  angular  patterns. 

ONYX  or  SARDONYX  is  made  up  of  regular  layers  one 
above  another  of  different  colours,  often  black,  white,  and 
red.  It  is  much  used  for  cameos. 

FLINT  or  HORNSTONE. — Common  dull  varieties. 

3.  OPAQUE  VAEIETIES  : — 

JASPER  is  quartz  rendered  opaque  by  clay,  iron,  and 
other  impurities  ;  it  is  of  a  red,  yellow,  or  green  colour  ; 
sometimes  the  colours  are  arranged  in  ribands,  or  in 
other  fantastic  forms.  It  is  used  for  ornamental  work. 

BLOODSTONE  is  green  jasper  with  splashes  of  red  re- 
sembling blood-spots. 

2.    OPAL. 

Chemical  Composition. — Silica  and  water. 

Never  crystallized.  Fracture  conchoidal.  Specific 
gravity,  2'2.  Hardness,  6.  Can  be  scratched  by  quartz, 
and  thus  distinguished  from  it. 

Infusible.     It  is  generally  milk-white. 

Precious  or  Noble  Opal  exhibits  a  beautiful  play  of 
colours,  and  is  a  valuable  and  rare  gem.  The  common 
varieties  are  of  no  value. 

3.  TALC. 

Chemical  Composition. — Silica,  magnesia,  water  (pro- 
toxide of  iron). 

Usually  in  irregular  layers.  Nearly  opaque.  White 
or  green  ;  pearly  lustre  ;  greasy  feel.  Specific  gravity, 
2 -7.  Hardness,  1.  Easily  impressed  by  the  nail.  But 
impure  varieties  are  much  harder. 

Infusible.  [Yields  no  water  when  heated  in  a  glass 
tube.  Is  not  attacked  by  boiling  sulphuric  acid.] 

Its  greasy  feel  and  pearly  lustre  readily  distinguish  it. 

Mica,  which  is  often  confounded  with  it,  is  not  so  soft, 
has  not  a  greasy  feel,  and  can  be  split  into  very  thin  trans- 
parent layers.  Steatite  is  a  variety  often  applied  to  useful 
purposes. 


246  DISCRIMINATION    OF    MINERALS. 


4.    CHLORITE. 

Chemical  Composition. — Silica,  magnesia,  alumina,  pro- 
toxide of  iron,  water. 

Often  forming  rocks.  Opaque.  Green  of  various 
shades.  Lustre  pearly  or  dull.  Hardness,  1  to  2.  Very 
easily  cut  with  a  knife. 

Infusible.  [In  glass  tube  yields  water.]  Boiling  sul- 
phuric acid  extracts  from  it  magnesia,  alumina,  and  fer- 
rous oxide. 

Abundant.     Of  no  value. 

5.    SERPENTINE. 

Chemical  Composition. — Silica,  magnesia,  water  (ferrous 
oxide). 

Often  forming  rocks.  Never  crystallized.  Opaque. 
Green.  Lustre  resinous  or  dull.  Streak  white.  Hard- 
ness, 3.  Can  be  cut  with  a  knife.  Specific  gravity,  2-5. 

Infusible  except  in  thin  edges  ;  turns  white  in  blowpipe 
flame.  [Powder  decomposed  by  sulphuric  acid  like  chlorite. 
Gives  off  water  in  glass  tube.] 

Some  varieties  form  handsome  stone  for  slabs  and 
ornamental  work. 

Meerschaum,  which  is  soft  and  earthy,  and  nephrite 
(the  New  Zealand  Maori  greenstone),  which  is  as  hard  as 
quartz,  both  contain  silica  and  magnesia. 

6.    AUGITE   AND    HORNBLENDE. 

Chemical  Composition. — Silica,  lime,  magnesia,  ferrous 
oxide  (occasionally  alumina  and  fluorine). 

In  four,  six,  or  eight-sided  prisms,  exhibiting  cleavage 
in  some  directions.  Usually  opaque.  Green,  black,  or 
white.  Glassy,  pearly,  or  resinous  lustre.  Specific  gravity, 
3  to  3*5.  Hardness,  5  to  6.  Can  be  scratched  with  a 
knife,  using  pressure.  Scratched  by  quartz. 

Dark  varieties  visible. 

Augite  usually  occurs  in  stout  six  or  eight-sided  prisms 


DISCRIMINATION    OF   MINERALS.  247 

with  roof-like  terminations;  hornblende  in  long  slender 
prisms.  Asbestos  is  a  variety  composed  of  separable  fibres 
like  flax. 

Abundant  in  igneous  and  other  rocks.  Of  no  value. 
Asbestos  is  used  as  a  fire-proof  material. 

7.    CHRYSOLITE,    OR   OLIVINE. 

Chemical  Composition. — Silica,  magnesia,  protoxide  of 
iron. 

In  prisms  ;  but  usually  in  grains  or  lumps  resembling 
bottle  glass.  Transparent  or  opaque.  Green,  yellow,  or 
black.  Glassy  lustre.  Fracture  conchoidal.  Hardness,  6 
to  7.  Cannot  be  scratched  with  a  knife.  Specific  gravity, 
3-4. 

Infusible. 

In  appearance,  hardness,  and  infusibility  may  resemble 
tin  ore,  but  is  very  much  lighter  in  weight.  Differs  from 
obsidian  (volcanic  glass)  in  its  infusibility  and  superior 
hardness. 

Occurs  in  basalt  and  lava.     Of  no  value. 

8.    TOURMALINE. 

Chemical  Composition.  —  Silica,  alumina,  magnesia, 
boracic  acid,  fluorine,  oxides  of  iron  (lime  and  alkalies). 

In  prisms,  with  three,  six,  nine,  or  more  sides,  fur- 
rowed lengthwise,  terminating  in  low  pyramids.  Com- 
monly black  and  opaque  ;  rarely  transparent,  and  of  a  rich 
red,  yellow,  or  green  colour.  Glassy  lustre.  Fracture 
uneven.  Specific  gravity,  3*1.  Hardness,  7  to  8.  Can- 
not be  scratched  with  a  knife.  Not  scratched  by  quartz. 

Infusible. 

When  the  smooth  side  of  a  prism  is  rubbed  on  cloth  it 
becomes  electric  and  can  attract  a  small  piece  of  paper  ;  if 
the  prism  is  as  wide  as  a  pipe-stem,  when  one  side  is  heated 
for  a  moment  in  the  blowpipe  flame  the  opposite  side  be- 
comes electric  and  can  attract  paper  until  the  heat  spreads 
uniformly  through  the  crystal.  (On  this  account  tour- 
maline is  said  to  be  pyro-electric.) 


248  DISCRIMINATION   OF    MINERALS. 

Occurs  in  granite  and  slate.  Of  no  value  ;  except  the 
fine-coloured  transparent  varieties,  which  are  used  as  gems 
and  for  optical  purposes. 

9.    GARNET. 

Chemical  Composition.— Silica,,  alumina,  lime,  iron,  mag- 
nesia, manganese. 

Crystallized  in  dodecahedrons,  never  in  prisms.  Trans- 
parent or  opaque.  Generally  red  ;  also  brown,  green, 
yellow,  black,  white.  Glassy  or  resinous  lustre.  Fracture 
conchoidal  or  uneven.  Specific  gravity,  3-5  to  4-3.  Hard- 
ness, 6'5  to  7 *5.  Cannot  be  scratched  with  a  knife. 

Fusible  with  more  or  less  difficulty.  Eed  varieties 
impart  a  green  colour  to  borax  bead  owing  to  presence  of 
chromium. 

Common  in  gneiss  and  schists.  Fine-coloured  trans- 
parent varieties  (carbuncle,  cinnamon  stone,  almandine) 
are  used  in  jewellery. 

10.    TOPAZ. 

Chemical  Composition. — Silica,  alumina,  fluorine. 

In  prisms,  sometimes  furrowed  lengthwise,  variously 
terminated,  breaking  easily  across  with  smooth  brilliant 
cleavage. 

Transparent  or  semi-transparent.  White,  yellow, 
greenish,  bluish,  pink.  Glassy  lustre.  Specific  gravity, 
3'5.  Hardness,  8.  Scratches  quartz.  Is  scratched  by 
sapphire. 

Infusible,  but  often  blistered  and  altered  in  colour  by 
heat.  When  smooth  surfaces  are  rubbed  on  cloth  they 
become  strongly  electric  and  can  attract  small  pieces  of 
paper,  but  rough  surfaces  do  not  show  this.  The  brilliant 
cleavage  of  topaz  distinguishes  it  from  tourmaline  and 
other  minerals. 

Occurs  in  granite.  Used  in  jewellery.  The  topaz  be- 
comes electric  by  friction  much  easier  than  other  gems, 
such  as  the  balas  ruby,  which  it  may  resemble.  The  white 
topaz  resembles  the  diamond  ;  but,  unlike  diamond,  it  can 
be  scratched  by  sapphire. 


DISCRIMINATION    OF   MINERALS.  249 


11.    BERYL,    OR   EMERALD. 

Chemical  Composition. — Silica,  alumina,  glucina. 

In  six-sided  prisms.  Usually  green.  Transparent  or 
opaque.  Glassy  lustre.  Fracture  uneven.  Specific  gravity, 
2*7.  Hardness,  7  to  8.  Scratches  quartz. 

Infusible,  or  nearly  so,  but  becomes  clouded  by  heating. 

Occurs  in  granite  arid  schist.  Valuable  for  jewellery 
when  transparent  and  rich  glass  green  (emerald),  or  sea 
green  (aquamarine).  Opaque  crystals  of  large  size,  exceed- 
ing a -ton  in  weight,  have  been  found  in  North  America. 

12.    ZIRCON,    OR   HYACINTH. 

Chemical  Composition. — Silica,  zirconia. 

In  square  prisms,  terminated  by  pyramids,  and  in  octa- 
hedrons. Often  found  in  pebbles  and  grains.  Transparent 
or  opaque.  Wine  or  brownish  red,  grey,  yellow,  white. 
Glassy  lustre.  Fracture  usually  irregular,  but  in  one 
direction  it  can  be  split  so  as  to  exhibit  a  smooth,  even 
cleavage  face  having  an  adamantine  lustre  like  the  diamond. 
Specific  gravity,  4-0  to  5'0.  Hardness,  7*5.  Scratches 
quartz  ;  is  scratched  by  topaz. 

Infusible ;  the  red  varieties,  when  heated  before  the 
blowpipe,  emit  a  bluish  phosphorescent  light,  and  become 
permanently  colourless. 

Occurs  in  syenite,  granite,  basalt.  Clear  crystals  used 
in  jewellery,  in  jewelling  watches,  and  in  imitation  of 
diamond.  It  may  be  distinguished  from  diamond  by  its 
inferior  hardness,  and  in  not  becoming  so  readily  electric 
by  friction. 

13.    FELSPAR. 

Chemical  Composition. — Silica,  alumina,  potash  or  soda 
(lime). 

Crystallized  or  in  irregular  masses.  Opaque.  Usually 
flesh-red,  or  white,  or  of  various  dull  tints.  Glassy  or 
pearly  lustre.  Fracture  irregular  ;  but  in  some  directions 
it  splits  with  an  even,  glimmering,  cleavage  face.  Specific 


250  DISCRIMINATION"    OF   MINERALS. 

gravity,  2'3  to  2-8.  Hardness,  6.  Easily  scratched  by 
quartz.  Cannot  be  scratched  with  a  knife  without  greatest 
pressure. 

In  thin  edges  fusible  with -difficulty. 

Abundant  in  granitic  and  porphyritic  rocks.  No  value, 
By  its  decomposition  it  forms  porcelain  clay  or  kaolin. 

14.  MICA. 

Chemical  Composition.  —  Silica,  alumina,  magnesia, 
potash,  iron. 

Always  crystallized  in  thin  plates,  which  may  be  split 
into  extremely  thin  flexible  layers.  Transparent  in  thin 
layers.  Brown  or  black.  Lustre  glassy,  pearly,  or 
metallic.  Streak  white.  Specific  gravity,  2 -7  to  3*1. 
Hardness,  2  to  2*5.  Very  easily  scratched  with  a  knife. 

Infusible.  Differs  from  talc  in  not  having  a  greasy 
feel,  in  being  harder,  flexible,  and  affording  thinner  layers 
perfectly  transparent. 

Abundant  in  granite  and  schist ;  fine  particles  common 
in  sandstone.  Applied  to  various  uses  when  in  large  plates, 
otherwise  of  no  value.  Was  formerly  used  instead  of  glass 
in  windows. 

15.    ZEOLITES. 

This  name  is  used  for  a  large  class  of  silicates,  com- 
prising from  fifty  to  a  hundred  different  minerals,  which 
all  contain  water  as  an  essential  ingredient,  and  which 
melt  readily  before  the  blowpipe,  and  boil  up  owing  to 
the  disengagement  of  steam.  They  occur  filling  pores 
and  cavities  in  basalt,  lava,  and  other  rocks.  They  are 
usually  white  and  well  crystallized.  Can  be  scratched  with 
a  knife.  Of  no  value.  Silica,  alumina,  lime,  soda,  potash, 
and  water  are  the  principal  ingredients. 

16.    CORUNDUM,    OR    SAPPHIRE. 

Chemical  Composition. — Alumina. 

In  six-sided  prisms,  often  irregularly  shaped.  Some- 
times in  granular  masses.  Transparent  or  opaque.  Blue, 
black  ;  also  red,  green,  yellow,  white.  Glassy  lustre,  some- 


.DISCRIMINATION   OF   MINERALS.  251 

times  pearly.  Fracture  uneven  or  conchoidal.  Specific 
gravity,  3'9  to  4'2.  Hardness,  9.  Easily  scratches  topaz 
and  quartz.  In  hardness  it  is  only  inferior  to  the  diamond. 
Infusible. 

Occurs  in  river  sands  ;  in  granite,  felspar,  magnetic  iron, 
basalt.  As  a  gem  it  stands  next  in  value  to  the  diamond, 
but  its  tint  must  be  brilliant  and  clear.  The  blue  variety 
is  called  Sapphire,  the  most  esteemed  shade  being  deep 
velvet  blue  ;  the  blood-red  variety  is  the  Oriental  ruby, 
which  can  be  easily  distinguished  from  other  red  gems  by  its 
superior  hardness  ;  the  bright  yellow  variety  is  the  Oriental 
topaz,  distinguished  by  its  hardness  from  the  topaz,  yellow 
tourmaline,  and  false  topaz ;  the  bright  green  is  the 
Oriental  emerald ;  the  bright  violet,  Oriental  amethyst ; 
these  varieties  readily  scratch  the  emerald  (No.  11)  and 
amethyst  (see  quartz,  No.  1) ;  one  variety  exhibits  a  six- 
rayed  star  inside  the  prism,  and  it  is  called  the  Asterias. 
Dull  crystals  are  called  corundum,  and  grey  or  black 
granular  varieties  emery ;  these  two  kinds  are  used  for 
polishing  powder.  The  ruby  is  the  most  highly  prized 
form  of  this  mineral. 

17,    SPINEL. 

Chemical  Composition. — Alumina,  magnesia. 

In  octahedrons,  occurring  only  crystallized.  Usually 
red  and  transparent ;  also  white,  blue,  green,  yellow,  brown, 
black ;  the  dark  shades  usually  opaque.  Lustre  glassy. 
Fracture  conchoidal.  Specific  gravity,  3'5  to  4'0.  Hard- 
ness, 8.  Scratches  quartz. 

Infusible,  and  thus  distinguished  from  garnet  which  it 
may  resemble.  Colour  altered  transiently  by  heat.  Dis- 
tinguished from  zircon  by  its  superior  hardness  and  inferior 
specific  gravity. 

Occurs  in  river  sand ;  in  igneous  rocks,  gneiss,  limestone. 
The  bright  transparent  varieties  are  used  in  jewellery. 
When  red  it  forms  the  common  or  spinel,  or  balas-ruby, 
which  is  distinguished  from  the  Oriental  ruby  by  its  inferior 
hardness ;  bright  green,  chlorospinel ;  orange,  rubicelle  ; 
violet,  aim andine -ruby  ;  black,  pleonast. 


252  DISCRIMINATION   OF   MINERALS. 


18.    CHRYSOBERYL. 

Chemical  Composition. — Alumina,  glucina. 

In  prisms  or  tables.  Transparent  or  semi-transparent. 
Green.  Lustre  glassy.  Fracture  conch oidal ;  imperfect 
cleavage.  Specific  gravity,  3-5  to  3-8.  Hardness,  8*5. 

Infusible  and  unaltered  before  the  blowpipe. 

Distinguished  from  beryl  by  its  specific  gravity,  its 
tabular  crystallization,  and  its  entire  infusibility. 

Occurs  with  beryl  in  river  sand,  gneiss  and  granite. 
Pellucid  and  fine  opalescent  varieties  are  used  as  gems. 


19.   DIAMOND. 

Chemical  Composition. — Carbon . 

In  octahedrons,  tetrahedrons,  dodecahedrons,  and  forms 
related  to  these  ;  the  faces  of  the  crystal  sometimes  curved. 
Transparent.  Colourless,  yellow,  red,  green,  blue,  white, 
brown,  or  black.  Lustre  adamantine.  Breaks  with  smooth 
cleavage  planes  parallel  to  the  octahedral  faces.  Specific 
gravity,  3*5  ;  loses  10-35thsof  its  weight  in  water.  Hard- 
ness, 10.  It  is  the  hardest  substance  known,  and  scratches 
all  other  minerals  and  gems. 

Infusible.  It  burns  and  is  consumed  at  a  high  tempe- 
rature. 

Becomes  strongly  electric  when  rubbed,  and  can  then 
attract  light  objects  ;  other  gems  do  not  exhibit  this  pro- 
perty unless  polished.  Some  varieties,  after  exposure  to 
the  sun,  are  said  to  give  out  light  when  placed  in  the  dark. 

The  distinguishing  characters  of  diamond  are,  its  hard- 
ness, crystalline  form,  clean  fracture,  its  brilliant  reflection 
and  adamantine  lustre,  the  facility  with  which  it  may  be 
electrified  by  friction,  and  a  peculiar  sound  on  rubbing 
together. 

Diamonds  have  been  found  in  quartz-conglomerate  and 
micaceous  sandstone,  but  are  mostly  obtained  in  river  beds. 


DISCRIMINATION   OF   MINERALS.  253 

N 

1>0.    GRAPHITE,    OR   BLACKLEAD. 

Chemical  Composition. — Carbon. 

In  six-sided  prisms ;  but  usually  in  uncrystallized 
wavy  layers.  Opaque.  Black.  Lustre  metallic.  Specific 
gravity,  2.  Hardness,  1  to  2.  Very  easily  cut  with  a  knife. 
Has  a  greasy  feel ;  marks  paper  like  a  lead  pencil. 

Infusible.     Burns  slowly  away. 

Molybdenite  and  foliated  tellurium  resemble  graphite  ; 
the  former  has  a  paler  colour  than  graphite,  and  the  latter 
is  very  easily  fusible. 

Occurs  in  gneiss  and  slate.  Valuable  for  lead  pencils 
and  crucibles. 

21.    COAL. 

Coal  and  carbonaceous  shale  differ  from  all  the  minerals 
which  they  may  resemble  by  burning  before  the  blowpipe 
and  leaving  a  white  or  brown  ash.  The  quantity  of  ash 
affords  an  estimate  of  the  purity  of  the  coal. 


22.    APATITE. 

Chemical  Composition. — Phosphoric  acid,  lime,  fluorine. 

In  six-sided  prisms.  Also  in  masses.  Transparent  or 
opaque.  Usually  green.  Sometimes  white,  yellow,  blue, 
red,  brown.  Lustre  resinous.  Fracture  conchoidal  or  un- 
even. Specific  gravity,  3 -2.  Hardness,  5.  Can  be  scratched 
with  a  knife,  using  pressure. 

Infusible,  except  on  very  thin  edges.  Some  kinds 
phosphoresce  when  heated.  The  pure  mineral  in  powder 
dissolves  slowly  in  nitric  acid  without  effervescence.  The 
crystals  may  resemble  beryl,  which,  however,  is  too  hard 
to  be  scratched  with  a  knife. 

Occurs  in  gneiss,  slate,  limestone.  Of  value  from  its 
use  in  the  manufacture  of  artificial  manures. 


254  DISCRIMINATION    OF   MINERALS. 


23.    FLUOR. 

Chemical  Composition. — Fluoride  of  calcium. 

In  cubes  or  octahedrons.  Also  in  masses.  Transparent 
or  opaque.  White  or  light  violet,  blue,  green  or  yellow  ; 
sometimes  layers  of  different  tints  in  the  same  piece.  Lustre 
glassy.  Breaks  with  smooth  cleavage  planes  parallel  to  the 
octahedral  faces.  Specific  gravity,  3*0  to  3'2.  Hardness 
4.  Can  be  scratched  with  a  knife,  but  not  so  easily  as 
calcite. 

Fusible  with  difficulty  ;  generally  flies  to  pieces  when 
heated.  Some  varieties  phosphoresce. 

Occurs  in  veins  with  lead  and  silver  ores,  Used  in 
etching  glass,  and  as  a  flux  in  smelting  ;  sometimes  for 
ornaments,  but  is  too  brittle.  Abundant  in  many  countries, 
and  of  little  value. 

24.    CALC-SPAR,    OR   CALCITE. 

Chemical  Composition. — Carbonic  acid,  lime. 

In  rhombohedrons  and  other  crystalline  forms.  Also 
massive,  earthy,  or  fibrous.  Transparent  or  opaque.  White 
when  pure  ;  often  tinted.  Lustre  glassy,  or  dull.  Breaks 
with  smooth  cleavage  planes  parallel  to  the  rhombohedral 
faces.  Specific  gravity,  2'5  to  2-8.  Hardness,  3.  Easily 
scratched  with  a  knife,  streak  white. 

Infusible  before  the  blowpipe,  but  emits  a  strong  light. 
When  burned,  as  in  a  kiln,  it  forms  quicklime.  Effervesces 
when  vinegar  is  poured  upon  it.  It  completely  dissolves 
in  nitric  acid  with  rapid  effervescence. 

Calc-spar  is  one  of  the  most  abundant  minerals  ;  it 
occurs  in  cavities  and  veins  of  all  kinds  of  rock.  The  term 
calc-spar  or  calcite  is  restricted  to  the  crystallized  variety. 
In  an  imperfectly  crystallized  and  compact  form  it  exists  in 
large  rocky  masses  and  beds  ;  all  marbles  and  limestones 
consist  of  it,  mixed  more  or  less  with  impurities.  Chalk 
and  stalactites  are  nearly  pure  calcium  carbonate.  All 
varieties  of  calcium  carbonate  may  be  easily  distinguished 


DISCRIMINATION   OF   MINERALS.  255 

by  being  scratched  with  a  knife,  giving  a  white  streak 
whatever  the  colour  of  the  mass  may  be,  by  effervescing 
with  an  acid,  and  by  being  infusible. 


25.    MAGNESITE. 

Chemical  Composition. — Carbonic  acid,  magnesia. 

In  rhombohedrons.  Also  globular,  compact,  earthy. 
Transparent  or  opaque.  White,  yellow,  brown.  Lustre 
glassy.  Cleavage  parallel  to  rhombohedral  faces.  Specific 
gravity,  2 -8  to  3*0.  Hardness,  4  to  5. 

Infusible.  Dissolves  in  nitric  acid,  with  very  slow  effer- 
vescence. Does  not  yield  quicklime  when  burnt. 

Occurs  with  serpentine  and  limestone.  Used  in  pre^ 
paring  Epsom  salts. 

23.    DOLOMITE. 

Chemical  Composition. — Carbonic  acid,  lime,  magnesia. 

In  rhombohedrons,  faces  often  curved.  Often  granular 
or  massive.  White,  or  dull-tinted.  Glassy  or  pearly. 
Specific  gravity,  2 -8  to  2*9.  Hardness,  3- 5  to  4. 

Infusible.  Effervesces  in  nitric  acid,  and  dissolves 
more  slowly  than  calc-spar.  Yields  quicklime  when  burnt. 
Occurs  in  extensive  beds  of  various  ages  like  limestone. 
Used  as  a  building  stone,  and  in  the  manufacture  of  Epsom 
salts.  Difficult  to  distinguish  from  calcite  without  chemical 
analysis. 

27.    ARAGONITE. 

Chemical  Composition. — Same  as  calc-spar. 

It  differs  from  calc-spar  in  its  crystalline  form,  which 
is  usually  difficult  to  discern.  It  often  occurs  in  fibrous 
clusters  or  in  tangled  branches.  Hardness,  3 -5  to  4-0. 
Specific  gravity,  2- 9. 

It  has  the  general  characters  of  calc-spar,  but  may  be 
distinguished  from  it  by  falling  to  powder  in  the  blowpipe 
flame,  as  well  as  by  its  superior  hardness. 


256  DISCRIMINATION   OF   MINERALS. 


28.    ROCK   SALT. 

Chemical  Composition. — Sodium  chloride. 

Has  the  characters  of  ordinary  table  salt,  but  is  more 
or  less  impure.  Occurs  in  beds  interstratified  with  sand- 
stones and  clays,  which  are  usually  of  a  red  colour  and 
associated  with  gypsum.  In  the  county  of  Cheshire, 
where  salt  mines  are  worked,  the  surface  indications  are 
brine  springs  supporting  a  vegetation  like  that  near  the  sea- 
coast  ;  also  occasional  sinking  of  the  soil  caused  by  the  re- 
moval of  the  subterranean  bed  of  salt,  by  spring  water  in 
some  cases,  and  by  mining  operations  in  others.  Small  and 
unimportant  quantities  of  salt  are  often  found  encrusting 
various  rocks  in  dry  weather. 

29.    SOLUBLE    SULPHATES. 

Aluminium  sulphate  alone,  or  combined  with  potash 
(alum),  and  magnesium  sulphate  (Epsom  salts),  are  often 
found  encrusting  rocks.  They  are  soluble  in  water  and 
easily  distinguished  by  their  taste. 

30.    NITRE. 

Chemical  Composition. — Potassium  nitrate. 

Mtre  or  saltpetre  is  another  soluble  mineral.  It  has  a 
cooling  taste.  It  can  be  easily  distinguished  by  the  vivid 
manner  in  which  it  burns  on  red-hot  charcoal. 


31.    GYPSUM,    SELENITE,    OR   ALABASTER. 

Chemical  Composition. — Sulphuric  acid,  lime,  water. 

In  prisms  with  oblique  terminations  ;  sometimes  resem- 
bling an  arrowhead.  Transparent  or  opaque.  White  or 
dull-tinted.  Glassy,  pearly,  or  satin  lustre.  Cleavage  occurs 
easily  in  one  direction.  Specific  gravity,  2- 3.  Hardness,  2. 
Yery  easily  cut  with  a  knife. 

fusible  with  difficulty.  In  the  blowpipe  flame  it  becomes 
white  and  opaque  without  fusing,  and  can  then  be  easily 


DISCRIMINATION    OF    MINERALS.  257 

crumbled  between  the  fingers.     Nitric  acid  does  not  cause 
effervescence. 

Occurs  in  fissures  and  in  stratified  rocks,  often  forming 
extensive  beds.  When  burnt  it  forms  plaster  of  Paris  ;  it  is 
also  used  for  ornaments,  and  as  a  manure. 

32.    HEAVY   SPAR,    OR   BARYTES. 

Chemical  Composition. — Sulphuric  acid,  baryta. 

In  tabular  glassy  crystals.  Also  in  dull  masses.  Trans- 
parent or  opaque.  White  or  tinted.  Specific  gravity,  4- 3 
to  4-8  ;  its  great  comparative  weight  readily  distinguishes 
it.  Hardness,  2*5  to  3*5 . 

Splinters  fly  off  the  crystals  when  heated  in  the  blow- 
pipe flame.  Fusible  with  difficulty.  Not  acted  upon  by 
acids. 

Occurs  with  various  ores.    Used  as  a  white  paint. 

S3.    SULPHUR. 

Crystallized  or  massive.  Yellow.  Resinous  lustre. 
Specific  gravity,  2-1,  Hardness,  1-5  to  2'5.  Fusible; 
burns  with  a  blue  flame  and  well-known  odour.  Occurs  in 
volcanic  regions,  and  in  beds  of  gypsum. 

34.    TIN   ORE. 

Chemical  Composition. — Tin  78'4,  oxygen  21-6. 

In  four-faced  prisms  and  pyramids,  having  an  ada- 
mantine lustre.  Also  in  masses  and  grains  (stream  tin) 
usually  dull ;  sometimes  resembling  wood  (wood  tin). 
Semi  transparent  or  opaque.  Brown  or  black  ;  streak  and 
powder  pale  blown.  Fracture  uneven.  Specific  gravity, 
6*8  to  7*0  ;  the  gieat  comparative  weight  is  an  important 
character  to  observe  in  distinguishing  tin  ore  from  other 
minerals.  Hardness,  6'0  to  7'0.  Cannot  be  scratched 
with  a  knife,  and  may  thus  be  distinguished  from  blende, 
which  it  resembles  in  lustre  and  infusibility. 

Infusible.  When  mixed  in  powder  with  sodium  carbo- 
nate, placed  on  charcoal  and  covered  with  a  small  piece  of 

s 


258  DISCRIMINATION    OF    MINERALS. 

potassium  cyanide,  and  then  heated  in  the  blowpipe  flame, 
a  malleable  globule  of  metallic  tin  is  obtained. 

Occurs  in  veins,  and  disseminated  in  granite,  schist, 
slate,  and  porphyry  ;  and  in  alluvial  deposits.  It  is  a  valu- 
able ore,  and  the  sole  commercial  source  of  the  metal. 

35.    MOLYBDENITE. 

Chemical  Composition. — Molybdenum  58*9,  sulphur 
41-1. 

In  thin  plates,  like  graphite  (No.  20).  Lustre  metallic. 
Colour,  lead  grey.  Specific  gravity,  4'5  to  4- 6.  Hardness, 
1-0  to  1-5.  Easily  scratched  by  the  nail. 

Infusible.  Tinges  blowpipe  flame  faint  green.  Heated 
on  charcoal  for  a  long  time,  it  gives  off  a  faint  sulphurous 
odour,  and  becomes  encrusted  white. 

Occurs  in  granite,  syenite,  and  chlorite  schist.  Not 
applied  to  any  particular  uses. 

36.    BISMUTH. 

Chemical  Composition. — Metallic  bismuth. 

Sometimes  crystallized  in  rhombohedrons  closely  re- 
sembling cubes,  but  generally  massive.  Lustre  metallic. 
White,  with  a  tinge  of  red,  liable  to  tarnish.  Brittle. 
Specific  gravity,  9'6  to  9*8.  Hardness,  2*0  to  2-5.  Easily 
scratched  with  a  knife. 

Easily  fusible.  Sometimes  gives  off  an  odour  of  gar  He, 
owing  to  admixture  of  arsenic. 

Occurs  with  cobalt,  silver,  and  tin  ores  in  granite  and 
slate  rocks.  Bismuth  is  a  very  valuable  metal. 

37.    ANTIMONY   SULPHIDE. 

Chemical  Composition. — Antimony,  72-9,  sulphur,  27'1. 

Usually  in  long  columnar  or  fibrous  crystals.  Also 
massive  and  granular.  Lustre  metallic.  Lead  colour. 
Often  tarnished.  Streak  metallic.  Specific  gravity,  4*6  to 
4*7.  Hardness,  2.  Very  easily  scratched  with  a  knife. 

Easily  fusible.  Before  blowpipe  gives  off  white  vapours 
and  an  odour  of  sulphur,  and  is  entirely  volatilised.  When 


DISCRIMINATION   OF    MINERALS.  259 

the  corner  of  a  large  piece  of  ore  is  fused,  the  border  of  the 
fused  part  is  often  tinted  red.  When  heated  on  charcoal 
with  cyanide  of  potassium,  it  gives  a  globule  of  metallic 
antimony,  which  is  brittle,  has  a  crystalline  surface,  burns 
when  strongly  heated,  emitting  white  fumes,  and  can  be 
entirely  volatilised. 

Occurs  in  veins  in  granite  and  slate,  alone,  or  with  ores 
of  silver,  lead,  and  other  metals.  This  ore  is  the  principal 
commercial  source  of  the  metal. 


38.    ARSENIC. 

Chemical  Composition.— Metallic  arsenic. 

Seldom  distinctly  crystallized.  Usually  in  fine  granular 
or  spherical  masses.  Colour  white,  usually  with  a  black 
tarnish.  Streak  white,  metallic.  Brittle.  Specific  gravity, 
5'7  to  5-8.  Hardness,  3'5. 

Before  the  blowpipe  it  quickly  volatilises  without  fusing, 
giving  off  white  fumes  having  an  odour  of  garlic. 

Occurs  in  veins  with  lead  and  silver  ores. 

39.    ARSENIC   SULPHIDE. 

Chemical  Composition. — Sulphur,  arsenic. 

In  crystals,  or  massive.  Yellow  or  red.  Semi-transparent 
or  opaque.  Eesinous  or  glassy  lustre.  Specific  gravity,  3'5. 
Hardness,  1*5.  Volatilised  before  the  blowpipe  with  a 
blue  flame. 

Occurs  in  veins  with  arsenical  ores  ;  in  beds  of  clay, 
limestone,  and  gypsum,  and  has  been  observed  in  lava. 
Used  as  a  pigment  and  in  making  fireworks,  but  objection- 
able for  each  of  these  uses,  owing  to  its  highly  poisonous 
character. 

40.    NATIVE    IRON. 

Chemical  Composition. — Iron,  with  a  small  percentage 
of  nickel. 

Occurs  in  meteorites.  Resembles  ordinary  iron.  Mal- 
leable. Is  attracted  by  a  magnet.  Specific  gravity,  7'0 

to  7-8. 


260  DISCRIMINATION    OF   MINERALS. 


41.    IRON    PYRITES. 

Chemical  Composition. — Iron,  46*7  ;  sulphur,  53- 3. 

In  cubes  and  allied  forms  ;  sides  often  marked  by  fine 
parallel  lines.  Also  massive.  Brass  yellow.  Lustre  metallic. 
Fracture  irregular.  Specific  gravity,  4*8  to  5- 1.  Hardness, 
6  to  6' 5.  Cannot  be  scratched  with  a  knife  ;  scratched  by 
quartz  ;  scratches  glass  with  great  facility.  Strikes  fire 
with  steel  (the  origin  of  the  term  pyrites). 

Before  the  blowpipe  it  burns  with  a  blue  flame,  giving 
off  an  odour  of  sulphur,  and  ultimately  fuses  into  a  black 
magnetic  globule. 

Abundant.  Used  as  a  source  of  sulphur  and  sulphuric 
acid ;  occasionally  auriferous.  This  ore  and  arsenical 
pyrites  form  the  '  mundic '  of  miners.  It  is  easily  dis- 
tinguished from  copper  pyrites  by  its  hardness  ;  copper 
pyrites  being  easily  cut  with  a  knife.  Distinguished  from 
gold  by  its  hardness  and  in  not  being  malleable,  and  in 
giving  off  sulphurous  odours  in  the  blowpipe  flame. 

42.    ARSENICAL  PYRITES  (MISPICKEL). 

Chemical  Composition. — Iron,  34-4;  arsenic,  19'6  ;  sul- 
phur, 46*0. 

In  flattened  prisms.  Also  massive.  White.  Lustre 
metallic.  Streak  grey.  Fracture  uneven.  Specific  gravity, 
6-0  to  6-3.  Hardness,  5'5.  Cannot  be  scratched  with  a 
knife  ;  scratched  by  quartz. 

Heated  before  the  blowpipe  it  gives  off  white  arsenical 
fumes  of  a  garlic  odour,  and  ultimately  fuses  into  a  black 
globule. 

Abundant  in  mining  districts  ;  sometimes  auriferous. 

This  ore  and  iron  pyrites  form  the  '  mundic '  of  miners. 

43.    MAGNETIC   IRON. 

Chemical  Composition. — Iron,  72-4  ;  oxygen,  27*6. 
In  octahedrons  and  dodecahedrons.     Also  in  masses 
(lodestone)  and  in  grains.     Black.     Lustre  metallic.    Streak 


DISCRIMINATION    OF   MINERALS.  261 

or  powder  black.  Fracture  irregular.  Specific  gravity, 
5-0  to  5*2.  Hardness,  5'5  to  6'5.  Not  scratched  with  a 
knife.  Magnetic  ;  it  can  attract  iron  filings.  Is  itself 
attracted  by  a  magnet. 

Infusible.  With  borax  bead  gives  the  indications  of 
iron. 

Occurs  in  many  rocks,  sometimes  in  beds,  or  forming 
mountainous  masses  ;  common  in  river  sands.  Used  as  an 
ore  of  iron. 

4      44.    SPECULAR   IRON,    HEMATITE,  OR   MICACEOUS   IRON. 

Chemical  Composition. — Iron,  70  ;  oxygen,  30. 

In  tabular  crystals  or  scales.  Also  fibrous,  massive, 
granular,  earthy.  Colour  black.  Streak  or  powder,  red. 
Lustre,  metallic  or  dull.  Specific  gravity,  4- 5  to  5 -3. 
Hardness  of  crystals,  5'5  to  6'5.  Not  scratched  with  a 
knife.  Earthy  varieties  softer,  and  can  be  scratched  with 
a  knife. 

Infusible.  With  borax  bead  gives  the  indications  of 
iron.  An  abundant  ore  of  iron.  Often  gradually  changes 
into  red  or  brown  ochre. 

45.    RED   FERRIC   OXIDE,    OR   RED    OCHRE. 

Chemical  Composition. — Iron  oxide,  and  more  or  less 
water. 

An  uncrystalline  earthy  variety  of  the  preceding,  often 
mixed  with  clay.  Colour,  bright  or  dull  red.  Can  generally 
be  scratched  with  a  knife. 

Blackens  when  heated,  but  regains  its  red  colour  on 
cooling.  With  borax  bead  gives  the  indications  of  iron. 
Abundant  ore  of  iron. 

46.    BROWN   FERRIC    OXIDE  (YELLOW   OR   BROWN    OCHRE). 

Chemical  Composition.— Iron  oxide,  water. 
..  Like  the  last,  but  of  a  brown,  yellow,  or  black  colour. 
Earthy,  fibrous,  stalactitic.     Scratched  with  a  knife. 

Blackens  before  the  blowpipe.  With  borax  bead  gives 
the  indications  of  iron.  An  abundant  ore  of  iron. 


262  DISCRIMINATION    OF   MINERALS. 


47.    TITANIC  IRON. 

Chemical  Composition. — Iron  oxides  and  titanic  acid  in 
variable  proportions. 

In  octahedrons  or  in  tabular  plates.  Also  in  grains. 
Black.  Lustre  metallic.  Streak  or  powder  black.  Specific 
gravity,  4-5  to  5*3.  Hardness,  5  to  6 '5.  Not  scratched 
with  a  knife. 

Infusible.  With  borax  gives  the  indications  of  iron. 
With  microcosmic  salt,  which  is  often  used  instead  of  borax 
in  an  exactly  similar  way,  it  gives  a  red  bead  in  the  re- 
ducing part  of  the  flame,  but  rather  a  large  quantity  of 
the  mineral  must  be  used  to  obtain  this  result. 

It  is  sometimes  magnetic. 

Its  black  streak  or  powder  distinguishes  it  from  specular 
iron,  which  it  often  resembles.  Common  in  some  river 
sand. 

48.    CHROMIC   IRON. 

Chemical  Composition. — Chromium  sesquioxide,  ferrous 
oxide  (alumina,  magnesia). 

In  octahedrons.  Usually  massive.  Black.  Lustre  faintly 
metallic.  Streak  or  powder  dark  brown.  Fracture  irregu- 
lar. Specific  gravity,  4*4  to  4-6.  Hardness,  5'5.  Not 
scratched  with  a  knife. 

Infusible.  With  borax  bead  gives  the  characteristic 
indications  of  chromium. 

Occurs  in  serpentine.  Used  in  the  preparation  of 
chromium  colours. 


49.    GREENEARTH. 

Chemical  Composition. — Iron  silicate,  and  other  ingre- 
dients. Has  a  green  earthy  appearance,  often  resembling 
an  ore  of  copper,  but  is  readily  distinguished  from  copper 
by  blowpipe  tests,  and  by  not  forming  a  blue  solution  in 
nitric  acid. 


DISCRIMINATION    OF   MINERALS.  263 


60.  IRON  CARBONATE. 

Chemical  Composition. — Carbonic  acid,  37*9  ;  ferrous 
oxide,  62-1. 

In  rhombohedrons ;  faces  often  curved.  Usually 
massive,  globular,  fibrous,  or  encrusting.  Light  or  dark 
brown.  Glassy  or  pearly  lustre.  Streak  white.  Specific 
gravity,  3*7  to  3-9.  Hardness,  3-oto4'5.  Scratched  with 
a  knife. 

Infusible.  Blackens  when  heated.  With  borax  bead 
gives  the  indications  of  iron.  Dissolves  in  nitric  acid  with 
effervescence  when  heated. 

Occurs  in  beds  and  nodules  in  stratified  rocks ;  in  veins 
and  cavities.  It  is  often  mixed  with  clay  (clay  ironstone). 
Abundant  ore  of  iron. 


51.    MANGANESE    ORES. 

Chemical  Composition. — Various  manganese  oxides. 

Crystallized  or  massive.  Black.  Lustre  unmetallic  ; 
dull  or  shining.  Powder  or  streak  brown  or  black.  Specific 
gravity,  4  to  5.  Hardness  generally  below  3.  Very  easily 
scratched  with  a  knife. 

Infusible.  With  borax  bead  gives  the  characteristic 
indications  of  manganese.  Widely  distributed.  Used  in 
chemical  manufactures. 


52.    ARSENICAL   NICKEL, 

Chemical  Composition. — Nickel  44,  arsenic  56. 

Usually  in  masses  of  a  pale  copper  colour  and  metallic 
lustre.  Specific  gravity,  7*2  to  7'8.  Hardness,  5  to  5*5. 
Scratched  with  a  knife,  using  pressure. 

Before  the  blowpipe  on  charcoal  it  melts,  giving  out 
white  arsenical  fumes  having  a  garlic  odour.  It  is  readily 
distinguished  by  its  pale  copper  red  colour  and  its  arsenical 
fumes  when  heated. 


204  DISCRIMINATION    OF    MINERALS. 

Occurs  in  veins  in  granite  and  slate,  with  ores  of  cobalt, 
silver,  copper,  bismuth,  lead.  A  valuable  source  of  metallic 
nickel. 

53.    SMALTINE    (TIN-WHITE    COBALT). 

Chemical  Composition. — Cobalt  up  to  24  per  cent., 
arsenic. 

In  octahedrons,  cubes,  dodecahedrons,  and  allied  forms. 
Also  massive.  Tin-white  or  steel-grey.  Lustre  metallic. 
Streak  grey isli -black.  Fracture  uneven.  Specific  gravity, 
6-3  to  6-6.  Hardness,  5-5. 

Fusible.  In  the  blowpipe  flame  gives  off  arsenical 
fumes  (odour  of  garlic).  With  borax  bead  gives  the 
characteristic  indications  of  cobalt.  In  nitric  acid  forms 
a  pink  solution.  Eesembles  mispickel  and  iron  pyrites, 
but  is  at  once  distinguished  by  the  test  with  borax  bead. 
Its  arsenical  fumes  distinguish  it  from  iron  pyrites,  and  its 
crystalline  form  from  mispickel. 

Occurs  in  veins  in  slate  and  gneiss.  A  valuable  ore  of 
cobalt. 

54.    COBALT    BLOOM. 

Chemical  Composition. — Cobalt  oxide,  37*6  ;  arsenic 
acid,  38-4  ;  water,  24-0. 

In  oblique  crystals,  with  a  highly  perfect  cleavage  like 
mica.  Also  in  incrustations.  Eed  or  pink,  grey,  green. 
Lustre  brilliant  pearly.  Transparent  or  opaque.  Specific 
gravity,  2*9  to  3'1.  Hardness,  1-5  to  2.  Very  easily  cut 
with  a  knife. 

Fusible  in  blowpipe  flame,  evolving  arsenical  fumes. 
When  heated  on  charcoal  it  gives  off  an  odour  of  arsenic. 
With  borax  bead  gives  indication  of  cobalt. 

Occurs  in  beds  and  veins  witli  other  ores  of  cobalt.  A 
valuable  ore  of  cobalt. 

55.    BLENDE. 

Chemical  Composition. — Zinc,  66'7  ;  sulphur,  33-3. 
In  dodecahedrons,  octahedrons,  and  allied  forms.    Also 
massive.     Yellow,  red,  brown,  black.     Lustre  adamantine, 


DISCRIMINATION    OF   MINERALS.  265 

resinous,  or  waxy.  Transparent  or  opaque.  Breaks  with 
brilliant  cleavage  faces  in  some  directions.  Specific 
gravity,  4'0  to  4-1.  Hardness,  3-5  to  4'0.  Easily  scratched 
with  a  knife. 

Infusible.  Emits  a  strong  light  when  heated,  but  no 
odour  of  sulphur  is  perceptible.  It  is  easily  distinguished 
by  its  waxy  lustre,  softness,  infusibility,  and  perfect  cleav- 
age. It  dissolves  at  once  in  nitric  acid. 

Occurs  with  lead  and  copper  ores.  It  is  the  '  black 
jack '  of  miners.  An  ore  of  zinc,  but  more  difficult  to 
smelt  than  the  carbonate  and  silicate. 

56.    ZINC   CARBONATE  (CALAMINE). 

Contains  5*2  per  cent,  of  zinc. 

Usually  in  crusts  or  masses.  White,  green,  or  brown. 
Opaque.  Pearly  or  glassy.  Specific  gravity,  4*1  to  4*5. 
Hardness,  5.  Can  be  scratched  with  a  knife,  using  a  little 
pressure. 

Infusible.  On  charcoal  becomes  yellow  whilst  hot, 
white  on  cooling.  Dissolves  rapidly  with  effervescence 
when  heated  with  nitric  acid. 

Occurs  with  galena  and  blende.     A  valuable  zinc  ore. 

57.    ZINC   SILICATE  (SMITHSONITfi). 

Contains  53  per  cent,  of  zinc. 

In  prisms,  or  massive.  White,  greenish,  bluish,  or 
brownish.  Glassy  lustre.  Transparent  or  opaque.  Specific 
gravity,  3*3  to  3-5.  Hardness,  5. 

Infusible.  Shines  with  a  green  light  in  the  blowpipe 
flame.  Does  not  effervesce  with  nitric  acid,  but  dissolves, 
leaving  a  jelly  of  silica. 

Occurs  with  zinc  carbonate.     A  valuable  zinc  ore. 

58.    GALENA. 

Chemical  Composition. — Lead,  86-6  ;  sulphur,  13 -4. 
In   cubes.      Also  granular,   massive.      Lead    colour. 
Metallic  lustre.      Streak   metallic.     Breaks   into   cubical 


266  DISCRIMINATION   OF   MINERALS. 

fragments  with  bright  cleavage  faces.  Specific  gravity, 
7'4  to  7'7.  Hardness,  2-5.  Very  easily  scratched  with  a 
knife. 

Easily  fusible.  Before  the  blowpipe  on  charcoal  is 
reduced  to  a  metallic  globule  of  lead,  giving  off  an  odour 
of  burning  sulphur. 

Occurs  in  granite  and  stratified  rocks.  Often  associated 
with  copper  and  other  ores.  The  principal  ore  of  lead. 
It  usually  contains  a  small  quantity  of  silver. 

59.  LEAD  CARBONATE  (CERUSITE). 

Contains  77  per  cent,  of  lead. 

In  prisms,  sometimes  united  in  four  or  six-rayed  crosses. 
White  or  grey.  Transparent  or  opaque.  Lustre  glassy. 
Specific  gravity,  6-4  to  6*6.  Hardness,  3* 5. 

Flies  violently  to  pieces  in  the  blowpipe  flame.  If 
placed  in  a  cavity  on  charcoal,  and  covered  with  sodium 
carbonate,  then  carefully  fused  by  the  flame,  it  yields  a 
globule  of  metallic  lead.  In  nitric  acid  it  dissolves  with 
effervescence. 

Usually  occurs  with  galena.     It  is  a  valuable  lead  ore. 

60.    LEAD  SULPHATE  (ANGLESITE). 

Contains  68  per  cent,  of  lead. 

In  slender  brilliant  crystals  upon  galena.  Also  massive. 
White  or  grey.  Transparent  or  opaque.  Specific  gravity, 
6-3.  Hardness,  3. 

Before  the  blowpipe  fusible,  but  apt  to  decrepitate  on 
charcoal ;  with  sodium  carbonate  yields  a  globule  of  me- 
tallic lead.  Differs  from  lead  carbonate  in  not  dissolving 
with  effervescence  in  nitric  acid. 

Usually  occurs  with  galena,  and  results  from  its  decom- 
position. 

61.    PYROMORPHITE    (LEAD    PHOSPHATE). 

Chemical  Composition. — Lead  oxide,  74*0,  phosphoric 
acid  15-8,  lead  chloride  10-2. 

In   stout    prisms,   grouped    together.      Also  massive. 


DISCRIMINATION   OF   MINERALS.  267 

Bright  green  or  brown.  Opaque  or  semi-transparent. 
Lustre  resinous.  Streak  white.  Fracture  irregular. 
Specific  gravity,  6*9  to  7*1.  Hardness,  3'5  to  4'0.  Easily 
scratched  with  a  knife. 

Easily  fusible.  With  sodium  carbonate  on  charcoal 
the  lead  is  reduced.  Soluble  in  nitric  acid. 

Occurs  sparingly  in  veins  with  galena. 

63.    CINNABAR. 

Chemical  Composition. — Mercury,  86*2;  sulphur,  13-8. 

In  granular,  compact,  and  earthy  masses.  Sometimes 
in  crystals,  exhibiting  adamantine  cleavage  faces.  Opaque 
or  semi-transparent.  Vermilion  or  brownish  red.  Specific 
gravity,  8*0  to  8-2.  Hardness,  2-5.  Very  easily  scratched 
with  a  knife. 

Before  the  blowpipe  it  volatilises,  giving  off  a  strong 
odour  of  burning  sulphur.  Mixed  with  dried  sodium  car- 
bonate, and  heated  over  a  candle-flame,  in  an  iron  spoon, 
it  gives  off  vapours  of  mercury,  which  may  be  condensed 
on  a  gold  coin  held  half  an  inch  above  the  mixture.  The 
surface  of  the  coin  appears  whitish  at  first,  but  when 
rubbed  between  the  fingers,  becomes  brilliantly  amalga- 
mated. With  care,  this  test  easily  detects  one  per  cent, 
of  cinnabar  in  an  ore.  The  mercury  is  removed  from  the 
gold  coin  by  gentle  heating.  The  blowpipe  tests  distin- 
guish it  at  once  from  red  oxide  of  iron  and  all  other  red 
minerals. 

Occurs  in  talcose  and  argillaceous  rocks.  It  is  the 
principal  source  of  the  mercury  of  commerce. 

63.    NATIVE   MERCURY,    OR   QUICKSILVER. 

The  metal  in  a  pure  state  is  rarely  found.  It  occurs 
disseminated  in  liquid  globules  through  sandstone  and 
other  rocks,  in  cavities  of  which  it  may  accumulate.  It  is 
easily  recognised.  A  rock  suspected  to  contain  mercury 
may  be  tested  by  simply  heating  it  as  described  under 
cinnabar  ;  but  without  the  addition  of  carbonate  of  soda. 


DISCRIMINATION    OF   MINERALS. 


64.    NATIVE    COPPER. 


Usually  in  strings,  plates,  or  irregular  masses :  some- 
times crystalline.  Like  ordinary  copper,  but  often  tar- 
nished. Specific  gravity,  8'9.  Easily  scratched  with  a 
knife.  Malleable,  can  be  flattened  out  under  a  hammer. 

Occurs  with  copper  ores. 


65.    VITREOUS   COPPER. 

Chemical  Composition. — Copper,  79-8  ;  sulphur,  20*2. 

Sometimes  in  prisms,  but  usually  massive.  Blackish 
lead  grey,  tarnished.  Streak  metallic.  Specific  gravity, 
5*5  to  5 -8.  Hardness,  2'5  to  3.  Very  easily  scratched 
with  a  knife. 

Fusible.  Before  the  blowpipe  gives  off  an  odour  of 
sulphur.  When  heated  on  charcoal,  a  malleable  globule 
of  metallic  copper  remains,  tarnished  black,  but  rendered 
evident  on  flattening  under  a  hammer.  With  borax  bead 
gives  the  indications  of  copper.  Dissolves  in  nitric  acid, 
forming  a  blue  solution.  (These  tests  distinguish  it  from 
sulphide  of  silver.) 

Occurs  with  other  copper  ores.  A  valuable  ore  of 
copper. 

66.    COPPER   PYRITES. 

Chemical  Composition. — Copper,  34'6  ;  iron,  30*9  ;  sul- 
phur, 34-9. 

In   tetrahedrons    or   octahedrons.      Usually   massive  , 
Brass  yellow,  often  tarnished.     Lustre  metallic.     Streak 
unmetallic,  blackish  green.     Fracture  uneven/     Specific 
gravity,  4*1  to  4'3.    Hardness,  3*5  to  4-0.    Easily  scratched 
with  a  knife. 

Fusible.     Gives  off  an  odour  of  sulphur  before  blow- 
pipe.    Does  not  give  the  indications  of  copper  with  borax 
bead,  or  when  heated  upon  charcoal  with  sodium  carbo 
nate.     Dissolves  in  nitric  acid,  forming  a  blue  solution. 
Distinguished  from  iron  pyrites  by  being  easily  cut  with  a 


DISCRIMINATION   OF   MINERALS.  269 

knife  ;  and  from  gold  by  not  flattening  under  a  hammer, 
and  by  its  greenish  powdery  streak. 

Occurs  in  granite  and  slate  in  lodes  or  veins.  Valuable 
ore  of  copper. 

67.    GREY   COPPER. 

This  term  includes  a  variety  of  ores  having  a  common 
crystalline  form,  generally  the  tetrahedron  also  ;  a  definite 
chemical  formula,  though  the  ingredients  are  numerous 
and  may  be  variously  combined  within  certain  limits. 
Sulphur  is  an  invariable  ingredient ;  and  arsenic  or  anti- 
mony, one  or  both,  must  be  present ;  the  other  ingredients 
are  copper,  iron,  zinc,  lead,  silver,  or  mercury,  in  variable 
proportions.  The  copper  ranges  up  to  40  per  cent.;  and 
in  some  kinds  as  much  as  30  per  cent,  of  silver  has  been 
found.  It  also  occurs  massive.  Steel  grey  to  iron  black. 
Lustre  metallic.  Streak  black,  or  dark  red  when  zinc  is 
present.  Fracture  uneven.  Specific  gravity,  4-5  to  5*2. 
Hardness,  3  to  4.  Can  be  easily  scratched  with  a  knife. 

Fusible.  Before  the  blowpipe  gives  off  an  odour  of 
sulphur,  also  white  inodorous  fumes  of  antimony,  and 
occasionally  arsenic. 

Copper  cannot  be  detected  by  the  blowpipe  tests.  It 
dissolves  in  nitric  acid,  forming  a  greenish  brown  solution. 

Occurs  with  copper  pyrites,  galena,  and  blende.  This 
ore  is  wrought  for  copper,  and  occasionally  for  silver. 


68.  BLACK   CUPRIC    OXIDE. 

Heavy  black  powder  or  mass.  Soft.  Easily  distin- 
guished from  manganese  by  affording  the  indications  of 
copper  by  the  blowpipe  tests.  It  results  from  the  waste 
of  various  copper  ores.  Valuable  as  a  source  of  the 
metal. 

69.  RED   CUPROUS   OXIDE. 

Chemical  Composition. — Copper,  88*8  ;  oxygen,  11/2. 
In  octahedrons  and  dodecahedrons.     Also  in  granular 
and  earthy  masses.     Bed.     Lustre  adamantine,  metallic, 


270  DISCRIMINATION    OF   MINERALS. 

or  earthy.  Streak  red.  Semi-transparent  or  opaque. 
Exhibits  cleavage  parallel  with  octahedral  faces.  Specific 
gravity,  6.  Hardness,  3-5  to  4-0.  Can  be  scratched 
with  a  knife. 

Before  the  blowpipe  on  charcoal  it  yields  a  globule  of 
metallic  copper.  With  borax  bead  gives  the  indications 
of  copper.  Forms  a  blue  solution  in  nitric  acid.  These 
tests  distinguish  it  from  red  ferric  oxide. 

Occurs  in  granite  and'  slate,  with  copper  ores  and 
galena.  Valuable  source  of  the  metal. 

70.  COPPER  CARBONATES,  BLUE  AND  GREEN. 

Chemical  Composition. — Oxide  of  copper,  carbonic  acid, 
water  ;  the  percentage  of  metallic  copper  about  56. 

In  crystals,  but  usually  in  fibrous,  silky,  globulrr 
encrusting  masses.  Blue  or  green.  Opaque.  Glassy,  silky, 
or  dull.  Specific  gravity,  3*7  to  4'0.  Hardness,  3*5  to 
4-0  ;  can  be  scratched  with  a  knife. 

Blacken  when  heated.  On  charcoal  are  reduced  to  a 
globule  of  pure  copper.  Give  the  indications  of  copper 
with  borax  bead.  Soluble  in  nitric  acid  with  effervescence, 
forming  a  blue  solution. 

Copper  Silicate  resembles  the  carbonate,  and  is  distin- 
guished by  dissolving  in  nitric  acid  without  effervescence. 

Occur  with  copper  ores,  and  result  from  their  decom- 
position. Valuable  sources  of  the  metal. 

71.    PLATINUM. 

In  flattened  or  angular  grains  or  nuggets,  which  are 
malleable.  Steel-grey.  Lustre  metallic.  Specific  gravity, 
17  to  19.  As  heavy  as  gold,  and,  therefore,  easily  distin- 
guished and  separated  from  lighter  materials. 

Infusible.     Insoluble  in  nitric  acid. 

Occurs  in  quartz  veins,  but  principally  in  alluvial 
deposits  with  gold.  Used  chiefly  for  chemical  apparatus. 
Of  great  value. 


DISCRIMINATION   OF   MINERALS.  271 


72.   GOLD. 

In  dust,  grains,  or  nuggets  in  river  sand ;  or  in  wiry, 
branching,  and  irregular  forms  in  quartz.  Pale  or  deep 
yellow.  Malleable.  Specific  gravity,  15  to  19.  Hard- 
ness 2-5  to  3-0. 

Fusible  without  blackening,  and  without  giving  off 
any  odour.  Imparts  no  colour  to  boiling  nitric  acid. 

The  minerals  commonly  accompanying  gold  are  iron 
pyrites,  arsenical  iron,  iron  and  manganese  oxides,  galena, 
and  copper  pyrites  in  quartz  veins  ;  and  magnetic  iron, 
titanic  iron,  chromic  iron,  tin  ore,  quartz,  zircon,  topaz, 
corundum,  diamond,  in  alluvial  deposits. 


73.  SILVER. 

In  strings,  plates,  and  branching  forms  penetrating 
quartz,  porphyry,  slate,  granite.  Silver  white,  but  usuallv 
tarnished  black.  Malleable.  Specific  gravity,  about  10- 5. 
Hardness,  2-5  to  3. 

Fusible  without  giving  off  any  odour.  Soluble  in 
nitric  acid,  and  on  adding  salt  to  the  solution,  a  white 
curd  is  thrown  down  which  blackens  on  exposure  to  sun- 
light. 

74.    SULPHIDE    OP   SILVER, 

Chemical  Composition. — Silver,  87  ;  sulphur,  13. 

In  dodecahedrons  or  allied  forms.  Also  massive. 
Black.  Opaque.  Lustre  metallic.  Streak  shining.  Specific 
gravity,  7*2.  Hardness,  2'0  to  2*5.  Very  easily  cut  with 
a  knife. 

Very  fusible,  giving  off  an  odour  of  sulphur  when 
heated.  Before  the  blowpipe  on  charcoal,  with  or  with- 
out sodium  carbonate,  it  yields  a  white  globule  of  metallic 
silver  which  can  be  flattened  under  a  hammer. 

The  ore  is  soluble  in  nitric  acid,  and  on  adding  salt  to 
the  solution  a  white  curdy  precipitate  is  thrown  down, 
which  blackens  on  exposure  to  sunlight. 


272  DISCRIMINATION    OF   MINERALS. 

Occurs  in  veins  in  granite,  porphyry,  and  slate,  with 
arsenic,  silver,  and  lead  ores. 

75.   ANTIMONIAL   AND   ARSENICAL    SILVER   ORES. 

Several  ores  of  silver  contain  arsenic  and  antimony, 
as  well  as  sulphur ;  the  percentage  of  silver  in  these  ores 
varies  from  12  to  68.  Bed,  grey,  or  black.  Lustre  ada- 
mantine or  metallic.  Eed  streak.  Specific  gravity,  5  to 
6.  Hardness,  2  to  3.  Easily  scratched  with  a  knife. 

Fusible.  Before  the  blowpipe  give  off  an  odour  of 
sulphur,  or  arsenical  fumes  of  a  garlic  odour,  or  fumes  of 
antimony.  Heated  on  charcoal  with  sodium  carbonate 
afford  a  globule  of  metallic  silver. 

Nitric  acid  extracts  the  silver  from  these  ores,  forming 
a  solution  in  which  salt  throws  down  a  white  curd,  black- 
ening on  exposure  to  sunlight. 

76.    HORN   SILVER. 

Chemical  Composition.— Silver,  75- 3  ;  chlorine,  24*7. 
In  veins  with  silver  ores.  Greenish.  Waxy  lustre.  Hard- 
ness, 1-0  to  1-5.  Cuts  like  wax  or  horn. 

Very  easily  fusible.  Heated  with  sodium  carbonate, 
on  charcoal,  it  yields  a  globule  of  metallic  silver. 

77.    LEAD    AND   ANTIMONY   SULPHIDES. 

Lead-  or  steel-grey.  Lustre  metallic.  Hardness  not 
exceeding  3.  Specific  gravity  about  6. 

Fusible.  Give  off  an  odour  of  sulphur  and  white 
fumes  of  antimony  before  the  blowpipe  ;  and  with  sodium 
carbonate  on  charcoal  afford  a  bead  of  metallic  lead. 

78.    MERCURY,    LEAD,    SILVER,    OR   COPPER   SELENIDE. 

Gives  off  a  strong  odour  of  horseradish,  due  to  sele- 
nium, when  heated  before  the  blowpipe.  .  The  metal  may 
be  found  in  some  cases  by  sodium  carbonate  on  charcoal, 
in  others  by  the  use  of  nitric  acid. 


DISCRIMINATION    OF   MINERALS.  973 

79.    MILLERITE    (NICKEL    SULPHIDE). 

Chemical  Composition. — Nickel,  64-9  ;  sulphur,  35*1 . 
In  delicate  needles.     Brass-yellow.     Metallic  lustre. 
Fusible.     Hardness,  3  to   5.      Imparts  to  borax  the 
colour  of  nickel. 

80.    WHITE    NICKEL. 

Chemical  Composition. — Nickel,  28*3  ;  arsenic,  71*7. 

Same  colour,  hardness,  specific  gravity,  and  crystalline 
form  as  smaltine,  No.  53.  Often  contains  cobalt,  and 
graduates  into  smaltine,  with  which  it  is  usually  found. 

81.  RUTILE. 

Chemical  Composition. — Titanium  and  oxygen. 

In  crystals  and  masses.  Red  brown.  Streak  paler. 
Lustre  sub-metallic.  Hardness,  6'0  to  6 -5.  Specific 
gravity,  4'2  to  4'3. 

Infusible.  With  borax  bead,  yellowish-green  or  colour- 
less (oxidising),  dirty  violet  (reducing). 

82.  SPHENE. 

Chemical  Composition. — Titanic  acid,  silica,  lime. 

In  thin  wedge-shaped  crystals.  Yellow,  green,  brown. 
Transparent  or  opaque.  Lustre  adamantine.  Hardness, 
5  to  5'5.  Specific  gravity,  3*2  to  3*6.  Transparent  yellow 
bead  with  borax  when  hot. 

Fusible  with  difficulty  on  edges. 

83.    WOLFRAM. 

Chemical  Composition. — Tungstic  acid,  iron,  manga- 
nese. 

Crystals  or  masses.  Brownish,  black.  Lustre  shining 
or  dull.  Opaque.  Hardness,  5 -5.  Specific  gravity,  7 

to  8. 

Fusible  with  difficulty.  With  borax  gives  the  colour 
of  iron.  Characterised  by  its  great  weight.  Found  often 
with  tin  ores. 

T 


274  DETERMINATION   OF   MINERALS 


84.    PITCHBLENDE. 

Chemical  Composition.—  -Uranium,  84*8  ;  oxygen,  15-2* 
Massive.  Black,  opaque.  Eesinous  lustre.  Streak  black. 
Hardness,  5-5.  Specific  gravity,  6*4  to  6*7. 

Infusible.  With  borax  gives  yellow  bead.  Dissolves 
in  hot  nitric  acid,  forming  -a  yellow  solution. 

85.    MAGNETIC   IRON   PYRITES. 

Chemical  Composition. — Iron,  60-5;  sulphur,  39-5. 
Usually  massive.     Bronze  yellow,  tarnished.     Metallic 
lustre.     Feebly  magnetic.     Hardness,  3*5  to  4-5. 
Fusible. 

DETERMINATION   OF  MINERALS. 

The  following  scheme  *  will  show  how  a  mineral  may 
be  determined  by  means  of  the  tests  and  characters  already 
indicated. 

The  scheme  first  separates  minerals  into  two  divisions 
— namely,  those  which  possess  a  metallic  lustre,  and  those 
which  do  not ;  and  these  are  further  subdivided  into 
groups  by  means  of  other  characters. 

The  various  members  of  each  group  are  enumerated 
in  the  tables,  which  also  give  the  mode  of  discrimination. 

In  most  cases  it  is  easy  to  decide  whether  a  mineral 
possesses  a  lustre  like  a  polished  metal,  but  where  the 
lustre  is  less  decided,  there  is  room  for  a  difference  of 
opinion  ;  besides,  a  mineral  may  possess  a  metallic  lustre 
in  some  specimens,  and  not  in  others. 

To  provide  against  this,  any  mineral  about  which 
difficulty  may  arise  is  placed  in  both  divisions,  and  even  in 
several  groups  if  necessary.  The  mineral  blende  affords 
an  instance. 

From  inspection  of  the  scheme  it  will  be  observed  that 
valuable  metalliferous  minerals  possess,  as  a  rule,  a  metallic 
lustre,  are  heavy  in  proportion  to  their  bulk,  and  are  easily 
scratched  with  a  knife.  The  chief  exception  is  tin  ore, 

*  Drawn  up  by  Dr,  A.  M.  Thompson.      .: „• 


BEFORE   THE   BLOWPIPE.  275 

which  has  not  a  metallic  lustre,  and  which  cannot  be  im- 
pressed with  a  knife. 

In  testing  it  is  necessary  to  bear  in  mind  that  a  piece 
of  ore  may  consist  of  a  single  mineral  only,  either  pure,  or 
mixed  with  a  readily  distinguishable  gangue ;  or  it  may  be 
composed  of  finely  disseminated  particles  of  two  or  more 
metalliferous  minerals.  But  by  search  in  localities  where 
such  mixtures  occur,  pure  and  isolated  specimens  of  each 
kind  may  generally  be  found.  Moreover,  after  a  little 
practice  the  complication  of  characters  which  mixtures 
present  will  not  interfere  with  the  recognition  of  their 
components. 

The  scheme  is  not  expected  to  prove  an  infallible  means 
of  determining  minerals  in  all  possible  instances,  though 
previous  experience  has  shown  that  it  is  of  use  to  those 
who  have  learned  to  apply  the  tests  recommended  in  the 
former  part  of  this  chapter.  To  avoid  error,  it  is  necessary 
in  all  cases,  before  coming  to  a  decision,  for  the  observer 
to  be  convinced  that  the  mineral  under  examination  ac- 
tually possesses  all  the  characters  of  the  mineral  which  it 
is  supposed  to  be. 

Serious  mistakes  may  arise  by  drawing  inferences  from 
the  scheme  only,  and  neglecting  to  confirm  all  the  other 
characters.  In  performing  the  experiments  recommended, 
the  greatest  care  and  accuracy  are  needful ;  to  the  careless 
and  superficial  observer,  or  whoever  is  not  proof  against 
self-deception,  the  scheme  cani  be  of  little  use. 

The  characters  of  each  mineral  have  been  described  in 
the  preceding  pages. 


SCHEME  FOR  THE  DETERMINATION  OF  MINERALS. 

DIVISION  I.— Minerals  possessing  a  METALLIC  lustre. 

Experiment. — Heat  a  fragment  of  the  mineral  supported 
on  charcoal,  or  held  with  a  forceps,  in  the  oxidising  point  of 
the  blowpipe  flame. 

1.  An  odour  of  burning  sulphur  is  given  off.  (See 
Group  I.) 


276  DETERMINATION   OF   MINERALS 

2.  An  odour  of  garlic  is  given  off,  or  white  fumes  not 
having  an  odour  of  sulphur.     (See  Group  II.) 

3.  No  fumes  or  odour  given  off.     (See  Group  III.) 

Note. — An  odour  of  horseradish  indicates  Selenium  (78). 

DIVISION  II. — Minerals  which  do  NOT  possess  a  metallic 
lustre. 

Experiment. — Scratch  the  mineral  with  a  knife  or  sharp 
fragment  of  quartz  or  sapphire,  according  to  its  hardness ', 
and  observe  the  colour  of  the  streak. 

Note. — If  the  streak  is  metallic  the  unmetallic  lustre  is  due  to  tarnish.  See 
Division  I. 

A.  The  streak  is  black  or  coloured. 

Experiment. — Hold  a  fragment  of  the  mineral  on  char- 
coal, or  with  a  forceps,  in  the  oxidising  point  of  the  blowpipe 
flame. 

1.  Fumes  or  odour  given  off.     (See  Group  IV.) 

2.  No  fumes  or  odour  given  off.     (See  Group  V.) 

B.  The  streak  is  uncoloured, — that  is  to  say,  white,  or 
nearly  so. 

Experiment. — Try  to  scratch  a  smooth  surface  of  the 
mineral  with  a  splinter  of  quartz. 

3.  The  mineral  can   be  scratched  by  quartz.       (See 
Group  VI.) 

4.  The  mineral  cannot  be  scratched  by  quartz.     (See 
Group  VII.) 

Note  1. — The  determination  must  always  be  made  upon  pure  minerals,  free 
from  any  adhering  foreign  matter. 

Note  2. — Coal  and  carbonaceous  shale  are  distinguished  from  minerals  which 
they  may  resemble  by  burning  in  the  blowpipe  flame,  leaving  a  more  or  less 
copious  ash. 


BEFORE   THE    BLOWPIPE.  277 


GROUP  I. 

MINERALS   WHICH    HAVE   A    METALLIC    LUSTRE,    AND   WHICH    GIVE    OFF 

SULPHUR. 

Experiment. — Try  to  scratch  the  mineral  with  a  knife, 
and  observe  the  streak. 

I. — Not  scratched  with  a  knife  ;  scratches  glass  with 
great  facility. 

Pale  brass-yellow  or  white.     Iron  pyrites,  41. 

IE. — Scratched  with  a  knife  ;  does  not  scratch  glass 
easily. 

*  Streak  unmet allic. 

a.  Brass-yellow.     Solution  in  nitric  acid  blue.    Copper 
pyrites,  66. 

b.  Black  or  red.    Solution  in  nitric  acid  colourless,  but 
on  adding  salt  water  a  white  curd  of  precipitate  is  thrown 
clown  which  blackens  on  exposure  to  sunlight.     Mineral 
gives  off  white  fumes  before  the  blowpipe.     Antimonial  or 
arsenical  silver  ores,  75. 

c.  Lead-  or  steel-grey.     Abundant  wrhite  fumes  before 
the  blowpipe.     On  charcoal  with  sodium  carbonate  yields 
a  globule  of  metallic  lead.  Lead  and  antimony  sulphides,  77. 

d.  Red.    Wholly  volatile  before  the  blowpipe.    Mixed 
with  carbonate  of  soda  and  heated  in  an  iron  spoon  over  a 
candle  flame,  white  vapours  are  given  off  which  may  be 
condensed  on  a  gold  coin  held  a  little  above  the  mixture, 
covering  its  surface  with  a  brilliant  amalgam  wrhen  rubbed. 
Cinnabar,  62. 

Note.-  -The  streak  of  Grey  Copper  (see  "below)  may  be  unmetallic,  often  red. 
**  Streak  metallic. 

Experiment. — Try  fusibility  in  blowpipe  flame. 

A.  Infusible  : — 

e.  Lead-grey.    Very  soft.     In  thin  leaves.     Tinges  the 
blowpipe  flame  faint  green.     Molybdenite,  35. 

Note. — Magnetic  Iron  Pyrites  and  Vitreous  Copper  are  fusible  with  difficulty. 

B.  Fusible  : — (Easily,  except  k  and  m.) 


278  DETERMINATION   OF   MINERALS 


Experiment. — Heat  a  small  piece  (size  of  linseed) ,  free 
from  gangue,  on  charcoal  without  adding  sodium  carbonate, 
hold  first  in  oxidising  point  and  finish  in  reducing  point. 

f.  Wholly   volatile,  emitting  abundant    white    fumes. 
Mineral   has  a  lead-colour.     Crystallised  in  long  prisms. 
Antimony  sulphide ,  37. 

g.  Globule  of  metallic  lead  remains.     Mineral  has  a 
lead-colour.     Cubical  cleavage.     Galena,  58. 

h.  Abundant  white  fumes  given  off.  Mineral  has  a  lead 
or  steel  colour ;  and  when  heated  on  charcoal  with  sodium 
carbonate  affords  a  globule  of  metallic  lead.  Lead  and 
antimony  sulphides,  77. 

i.  Gobule  of  metallic  silver  remains  (facilitated  by 
adding  a  little  sodium  carbonate).  Mineral  has  a  black 
colour.  Is  .soluble  in  nitric  acid ;  on  adding  salt  water 
to  the  solution  a  white  curd  is  thrown  down  which  blackens 
on  exposure  to  sunlight.  Silver  sulphide,  74. 

k.  Globule  of  mstallic  copper  remains  (facilitated  by 
adding  a  little  sodium  carbonate) ;  discovered  by  crushing 
the  residue  and  flattening  it  under  a  hammer.  Mineral  has 
a  black  colour.  Does  not  give  off'  copious  white  fumes 
before  the  blowpipe.  It  forms  a  blue  solution  with  nitric 
acid.  Vitreous  copper,  65, 

/.  Slaggy  globule  remains,  usually  attracted  by  a 
magnet,  not  yielding  copper  when  crushed.  Mineral  has 
a  black  or  steel  colour.  It  gives  off  copious  white  fumes 
before  the  blowpipe.  It  forms  a  greenish-brown  solution 
with  nitric  acid.  Grey  copper,  67. 

m.  Greyish-black  magnetic  bead  remains.  Mineral 
has  a  bronze  or  copper  colour.  Can  be  scratched  with  a 
knife  ;  is  attracted  by  a  magnet ;  does  not  form  a  blue  or 
green  solution  with  nitric  acid.  Magnetic  iron  pyrites,  85. 

n.  Black  magnetic  globule.  Mineral  has  the  form  of 
brass  yellow  needles.  Nickel  sulphide,  79. 

N.B. — Before  determining  the  name  of  a  mineral,  it  is  necessary  to  compare 
it  with  the  description  to  which  the  number  refers. 


BEFORE   THE   BLOWPIPE.  279 


GROUP II. 

MINEBALS  WHICH  HAVE  A  METALLIC  LUSTRE  AND  WHICH  GIVE  OFF 
EITHER  AN  ODOUR  OF  GARLIC  WITHOUT  SULPHUR,  OR  WHITE  FUMES 
WHICH  HAVE  NOT  A  GARLIC  OR  SULPHUROUS  ODOUR. 

1.  The   fumes    evolved    have    an    odour    of   garlic 
(arsenic). 

*  Not  scratched  with  a  knife.     Scratches  glass. 

a.  White  metallic.     Eesidue  after  roasting  gives  indi- 
cations of  iron,  with  borax  bead.    Crystallised  in  flattened 
prisms.     Mispickel,  42. 

b.  White  metallic-     Eesidue  after  roasting  gives  indi- 
cations of  cobalt,  with  borax  bead.    Crystallised  in  octahe- 
drons.    Smaltine,  53. 

Note. —  White  Nickel  resembles  Smaltine,  and  is  found  with  it. 
**  Scratched  with  a  knife.     Does  not  scratch  glass. 

c.  Pale  copper  red.     Arsenical  nickel,  52. 

d.  Carmine  red.     Arsenical  silver  ore,  75. 

e.  White  (as  streak  shows),  tarnished  black  ;  wholly 
volatilised  by  heat.     Arsenic,  38. 

Note.— Metallic  Bismuth  is  frequently  associated  with  Arsenic.  Possibly 
Grey  Copper  and  Arsenical  Silver  may  be  looked  for  here ;  for  their  characters 
see  Group  I. 

2.  The  fumes  evolved  have  not  a  garlic  odour. 
Possibly  grey  copper,  antimonial  silver  ore,  lead  and 

antimony  sulphides,  or  cinnabar :  but  these  ores  generally 
give  off  a  faint  odour  of  sulphur  in  addition  to  white 
fumes.  For  their  characters,  see  Group  I. 

N.B. — Before  determining  the  name  of  a  mineral,  it  is  necessary  to  compare 
it  with  the  description  to  which  the  number  refers. 


280  DETEBMINATIOX    OF   MINERALS 


GROUP  III. 

MINERALS    WHICH    HAVE    A    METALLIC   LUSTRE,    AND    WHICH    GIVE    OFF 

NO   FUMES. 

I.  The  mineral  is  malleable  (can  be  flattened  under  a 
hammer). 

a.  Yellow.     Gold,  72. 

b.  Eed.     Copper,  64. 

c.  White,    rusty   surface ;    strongly   attracted     by   a 
magnet.     Iron,  40. 

d.  White,  feebly  or  not  attracted  by  a  magnet.     In- 
fusible.    Insoluble  in  nitric  acid.     Platinum,  71. 

e.  White,  often  tarnished ;  not  attracted  by  a  magnet. 
Fusible.     Soluble  in  nitric  acid  ;  on  adding  salt  water  to 
the  solution,  a  white  curd  is  thrown  down,  which  blackens 
on  exposure  to  sunlight.     Silver,  73. 

II.  The  mineral  is  brittle  (breaks  to  pieces  under  a 
hammer). 

Experiment. — Observe  the  colour  imparted  to  a  borax 
bead  in  oxidising  and  in  reducing 

1.  Violet  in  oxidising,  colourless  in  reducing. 

a.  Manganese  ores,  51. 

2.  Eed  (hot),  yellow  (cold),  in  oxidising,  bottle-green  in 
reducing. 

Scratch  the  mineral  with  quartz  and  observe  the  colour  of  the  streak. 

b.  Brown  streak  ;  mineral  not  attracted  by  a  magnet. 
Brown  iron  oxide,  46. 

c.  Eed  streak  ;  not  attracted  by  a  magnet.     Specular 
iron,  44. 

d.  Black  streak  ;  not  attracted  by  a  magnet.     Titanic 
iron,  47. 

e.  Black  or  brown    streak  ;  strongly   attracted   by   a 
magnet.     Magnetic  iron,  43. 

Note..—  Possibly   Wolfram  (83) ;  non-magnetic ;   streak  reddish-brown   or 
black ;  remarkable  for  its  great  weight. 


BEFORE   THE   BLOWPIPE.  281 

3.  Green  (hot),  blue  (cold),  in  oxidising,  red  in  reducing. 
Red  cuprous  oxide ,  69. 

4.  Green  in  oxidising,  green  in  reducing. 
/.   Chromic  iron,  48. 

5.  Colourless. 

*  Infusible. 

Minerals  HARDER  than  calc-spar. 

g.  Eeadily  soluble  in  nitric  acid.  Scratched  with  a 
knife.  Blende.  55. 

h.  Insoluble  in  nitric  acid.  Not  scratched  with  a  knife. 
With  potassium  cyanide  upon  charcoal,  yields  a  globule  of 
metallic  tin.  Tin  ore,  34. 

Minerals  SOFTER  than  calc-spar. 

i.  Black,  like  black-lead.  Specific  gravity  about  2. 
Graphite,  20. 

k.  Lead-colour.  Specific  gravity  about  4-5.  Tinges 
blowpipe  flame  pale  green.  Molybdenite,  35. 

**  Fusible. 

Heated  on  charcoal  forms  an  incrustation  which  is  red 
whilst  hot,  yellow  when  cold.  Bismuth,  36. 

6.  Note. —  Green  in  oxidising,  dirty  violet  in  reducing,  indicates  Rutile  (81), 
yellow  in  oxidising,  green  in  reducing  (difficult  to  obtain  in  a  candle  flame), 
atforded  by  a  black  mineral,  soluble  in  boiling  nitric  acid,  forming  a  yellow 
solution,  indicates  Pitchblende  (84). 

Note. — Mica  may  possibly  be  sought  for  in  this  group.  It  is  distinguished 
by  its  lightness  of  weight,  and  its  capability  of  being  split  into  very  thin,  trans- 
parent, flexible  layers. 

N.B. — Before  determining  the  name  of  a  mineral,  it  is  necessary  to  compare 
it  with  the  description  to  which  the  number  refers. 

GROUP  IV. 

MINERALS  WHICH  POSSESS  AN  UNMETALLIC  LUSTRE,  A  COLOURED  STREAK, 
AND  WHICH  GITE  OFF  FUMES  OR  ODOUR  WHEN  HEATED  BEFORE  THE 
BLOWPIPE. 

a.  Colour  and  streak  yellow,  entirely  volatile,  burning 
with  a  blue  flame  and  sulphurous  odour.     Sulphur,  33. 

b.  Colour  red,  orange,  or  yellow,  entirely  volatile,  burns 


282  DETERMINATION   OF   MINERALS 

on  charcoal  with  a  blue  flame  and  garlic  odour.     Arsenic 
sulphide,  39. 

c.  Streak  red.     Strong  odour  of  garlic  or  white  fumes 
(of  antimony)  when  heated.     Dissolved  in  nitric  acid  ;  on 
adding  salt  to  the  solution  a  white  curd  is  thrown  down 
which  blackens  on  exposure   to  sun-light.     Arsenical   or 
antimonial  silver  ore,  75, 

d.  Streak   red.      Wholly   volatile   before    blowpipe. 
Mixed  with  sodium  carbonate  and  heated  in  an  iron  spoon 
over  &  candle-flame,  vapours  are  given  off  which  may  be 
condensed  on  a  gold  coin  held  a  little  above  the  mixture, 
covering  its  surface  with  a  brilliant  amalgam  when  rubbed. 
Cinnabar,  62. 

N.B. — Before  determining  the  name  of  a  mineral,  it  is  necessary  to  compare 
it  with  the  description  to  which  the  number  refers. 

GROUP  V. 

MINERALS  WHICH  POSSESS  AN  UNMETALLIC  LUSTRE,  A  COLOURED  STREAK, 
BUT  WHICH  GIVE  OFF  NO  FUMES  OR  ODOUR  BEFORE  THE  BLOWPIPE. 

Experiment. — Observe  the  colour  imparted  by  the  mine,  al 
to  a  borax  bead,  both  in  oxidising  and  reducing. 

1.  Green  (hot),  blue  (cold),  in  oxidising;  red  in  reduc- 
ing (difficult  to  obtain). 

a.  Colour  of  mineral  blue  or  green.     Copper  carbonate, 
70. 

b.  Colour  of  mineral  red.     Bed  cuprous  oxide,  69. 

c.  Colour  of  mineral  black.     Black  cuprous  oxide,  68. 

2.  Green  in  oxidising,  green  in  reducing. 

d.  Colour  of  mineral  black.     Chromic  iron,  48. 

3.  Red  (hot),  yellow  (cold),  in  oxidising  :  bottle-green  in 
reducing. 

e.  Colour  of  mineral  green.     Greenearth,  40. 

/.  Colour  of  mineral  brown  ;  blackened  during  heating. 
Brown  ferric  oxide,  46. 

g.  Colour  of  mineral  red;  blackened  during  heating. 
Red  ferric  oxide,  45. 

Note. — Iron  Ar&eniate  is  green  or  yellow,  Iron  Phosphate  is  blue. 


BEFORE   THE    BLOWPIPE.  283 

4.  Amethyst  in  oxidising,  colourless  in  reducing. 

h.  Colour  of  mineral  brown  or  black.  Manganese 
ores,  51. 

Note. — Manganese  Carbonate  is  rose  red  or  brownish,  streak  white. 

5.  Colourless  in  both  oxidising  and  reducing. 

i.  Easily  scratched  with  a  knife.  Cleavage.  Soluble 
in  nitric  acid.  Blende,  55. 

k.  Not  scratched  with  a  knife.  No  cleavage.  Heated 
with  potassium  cyanide  upon  charcoal  yields  a  malleable 
globule  of  metallic  tin.  Tin  ores,  34. 

Note. — Cobalt  Bloom  (54)  has  a  red  colour  and  streak ;  it  gives  the  indica- 
tions of  Cobalt  with  borax  bead.  Buttle,  Wolfram,  and  Pitchblende  might  be 
considered  to  have  an  unmetallic  lustre.  See  under  Group  III. 

N.B. — Before  determining  the  name  of  a  mineral,  it  is  necessary  to  compare 
it  with  the  description  to  which  the  number  refers. 


GROUP  VI. 

MINERALS   WHICH   HAVE   AN    UNMETALLIC    LUSTRE,  AND   WHICH    ARE 
SCRATCHED    BY   QUARTZ,    SHOWING    A   WHITE    STREAK. 

I. — Minerals  soluble  in  water  (having  a  taste). 

a.  Taste  of  common  table  salt.     Salt,  28. 

b.  Sweetish  astringent  taste.     Alum,  29. 

c.  Bitter  taste  of  Epsom  salts.     Epsomite,  29 

d.  Cooling   taste.       Causes   vivid    combustion    when 
thrown  on  a  piece  of  red-hot  charcoal.     Nitre,  30. 

Note. — Zinc   (white),  Iran   (green),  and  Copper  (blue)   sulphates  have  a 
nauseous  metallic  taste* 

n. — Minerals  insoluble  in  water ;  but  soluble  in  nitric 
acid  (best  determined  by  placing  a  very  little  of  the 
powder  in  a  test  tube,  pouring  on  it  a  few  drops  of  the 
acid,  and  heating  if  requisite). 

N.B.— All  of  these  can  be  scratched  mth  a  knife. 
*  Easily  fusible. 

a.  Green,  yellow  or  brown,  Hardness,  3  to  4.  Glo- 
bule of  lead,  on  charcoal  with  sodium  carbonate.  No 
effervescence  in  nitric  acid.  Pyromorphite,  61. 


'284  DETERMINATION   OF   MINERALS 

b.  White  or  grey.    Hardness,  3  to  4.     Flies  violently  to 
pieces  in  the  blowpipe  flame.     Globule  of  lead  on  char- 
coal with  sodium  carbonate.     Effervesces  in  nitric  acid. 
Cerusite,  59. 

Note. — White  or  grey.     Effervesces  in  nitric   acid.     Specific   gravity  4-3. 
Does  not  fly  to  pieces  when  heated ;  yields  no  metal  on  charcoal,  WITHERTTE 

BARIUM  CARBONATE. 

**  Infusible. 

c.  Hardness,  3.    Dissolves  with  very  brisk  effervescence 
in  cold  nitric  acid.     Does  not  crumble  to  powder  in  the 
blowpipe  flame.     Calc-spar,  24. 

d.  Hardness,  3'5  to  4.     Dissolves  like  calc-spar ;  but 
crumbles  to  powder  in  the  blowpipe  flame.     Aragonite,  6. 

e-  Hardness,  3- 5  to  4.  Dissolves  much  slower  than 
calc-spar  ;  but  difficult  to  distinguish  without  chemical 
analysis.  Dolomite,  26. 

/.  Hardness,  4  to  5.  No  effervescence  in  cold  nitric 
acid,  very  slight  in  hot.  Magnesite,  25. 

g.  Hardness,  3*5  to  4'5.  Effervescence  in  hot  nitric 
acid.  The  mineral  blackens  when  heated  in  the  blowpipe 
flame ;  it  gives  the  indication  of  iron  with  borax.  Iron 
carbonate,  50. 

h.  Hardness,  5.  Effervescence  in  hot  nitric  acid. 
Heated  on  charcoal  with  sodium  carbonate  it  forms  a 
crust  which  is  yellow  whilst  hot.  Calamine,  56. 

i.  Hardness,  5.  Dissolves  in  nitric  acid  without  effer- 
vescence, leaving  a  jelly  of  silica.  In  blowpipe  flame  it 
shines  with  a  green  light.  Zinc  silicate,  57. 

k.  Hardness,  3'5.  Effervesces  in  hot  nitric  acid.  Flies 
violently  to  pieces  in  the  blowpipe  flame.  On  charcoal 
with  sodium  carbonate  yields  a  globule  of  lead.  Cerusite, 
59. 

/.  Hardness,  3-5  to  4.  Brilliant  cleavage.  Eapidly 
soluble  in  nitric  acid  with  effervescence.  Heavy  (specific 
gravity,  4).  Blende,  55. 

m.  Hardness,  4'5  to  5.  Slowly  soluble  in  nitric  acid 
without  effervescence.  Apatite,  22. 

Note.— Hardness,  3'5.     Effervesces  in  hot  nitric  acid.     Tinges  the  blow-pipe 
flame  crimson.     Strontianite  (Strontium  carbonate).  ,'/Y(;,  !.'•,) 


BEFORE  THE:  BLOWPIPE.  285 

III. — Minerals  insoluble  in  both  water  and  nitric  acid. 

*  Easily  fusible. 

HARDNESS. 

1*0  to  1*5.  Like  wax.  On  charcoal  with  sodium  carbon- 
ate yields  a  globule  of  silver.  Horn  silver, 
76. 

2 '5  to  3*0.  White  or  grey.  On  charcoal  with  sodium 
carbonate  yields  a  globule  of  lead.  Angle- 
site,  60. 

3/5  to  4*0.  Green  or  brown.  On  charcoal  with  sodium 
carbonate  yields  a  globule  of  lead.  Pyro- 
morphite,  61. 

3'5  to  6'5.  Usually  white.  Swell  up  before  the  blowpipe. 
Occur  in  cavities  of  rocks.  Zeolites,  15. 

5*0  to  6'0.  Black,  green,  or  white.  Prisms,  fibrous  or 
flaxlike.  Hornblende  and  augite,  6. 

6*5  to  7 '5.  Usually  red.  Crystallised  in  dodecahedrons. 
Garnet,  9. 

Note. — Glaxs  (artificial)  maybe  included  here;  easily  distin- 
guished by  its  appearance,  easy  fusibility,  and  inferior  hard- 
ness, 4-5  to  5-5. 

**  Infusible,  or  not  easily  fusible. 

1-0  to  1'5.     Light  green.     In  layers.    Unctuous.     Talc,§. 
L'5.     Dark  green.     In  layers  or  granular.     Some- 
times fusible  to  a  black  glassy  bead.     Chlo- 
rite, 4. 

2'0  to  3'5.     Green.  Turns  white  in  blowpipe  flame.    Feels 

often  greasy.     Serpentine,  5. 

2-0.  Usually  white.  After  heating  becomes  opaque, 
and  can  be  rubbed  to  powder  between  the 
fingers.  Fusible  with  difficulty.  Gypsum ^\. 

2*0  to  2-5.  Grey  or  black.  Can  be  split  into  extremely 
thin  semi-transparent  flexible  layers.  Mica, 
14. 

3*0  to  3*5.  White  or  grey.  Tabular  crystals  or  massive. 
Heavy  (specific  gravity,  4*3  to  4*8).  Splinters 
fly  off  crystals  when  heated.  Fusible  with 
difficulty.  Heavy  spar,  32. 


236  DETERMINATION   OF   MINERALS 


HARDNESS. 


4-0.  Cubes  or  massive.  Octahedral  cleavage.  Flies 
to  pieces  when  heated.  Specific  gravity,  3 
to  3-2.  Fusible  with  difficulty.  Fluor-spar, 
23. 

V;V  5'0.  Six-sided  prisms,  massive.  Green  or  white. 
Specific  gravity,  3  to  3*3.  Generally  flies 
to  pieces  when  heated.  In  fine  powder, 
slowly  soluble  in  nitric  acid.  Apatite,  22. 
5-0  to  6*0.  Prisms,  fibrous  or  flaxl'ike.  Cleavage.  Green, 
black,  or  white.  Generally  fusible,  Specific 
gravity,  2'9  to  3*5.  Hornblende  and  augite,  6. 

Note.— Possibly  Epidote.  Yellowish  green.  Hardness,  6*0 
to  7-0. 

6'0.  Prisms  or  massive.  Flesh  colour,  white,  or 
tinted.  Cleavage.  Specific  gravity,  2'3  to 
2-8.  Felspar,  13. 

6-0  to  7*0.  Masses  or  grains  like  glass.  Black  or  green. 
Specific  gravity,  3-3  to  3-6.  Chrysolite,  7. 

6 '5  to  7 '5.  Dodecahedrons.  Usually  red.  Generally  fusi- 
ble. Bed  infusible  varieties  impart  a  green 
colour  to  borax  bead.  Specific  gravity,  3*5 
to  4-3.  Garnet,  9. 

5-5  to  6-5.    Never  crystallised.  White,  tinted,  or  chatoyant. 

Specific  gravity,  1-9  to  2'3.     Opal,  2. 
7*0.      Six-sided    prisms.       Specific    gravity,    2'6. 
Quartz,  1. 

Note. — Sphene  (82)  occurs  in  acute  thin  crystals.  Yellow, 
green,  or  brown.  Specific  gravity,  3'2  to  3'6. 

Chiastolite  and  other  Aluminium  Silicates  occur  in  prisms. 
Brown  or  white.  Opaque.  Hardness,  6  to  7 '5.  Infusible. 
Specific  gravity,  3  to  37. 

N.B. — Before  determining  the  name  of  a  mineral,  it  is  neces- 
sary to  compare  it  with  the  description  to  which  the  number 
refers. 


BEFORE   THE   BLOWPIPE.  287 


GROUP  VIL— Including  the  Gems. 

MINERALS   WHICH    HAVE   AN    UNMETALLIC    LUSTRE,  AND   WHICH    ARE 
NOT   SCRATCHED   BY   QUARTZ. 

Note. — Tin  ore  (34)  may  occur  here.  Hardness,  6  to  7.  Remarkable  for  its 
great  weight.  Specific  gravity,  6'8  to  7-0.  Brown  or  black.  With  cyanide 
of  potassium,  on  charcoal,  yields  a  globule  of  Tin. 

GEMS. 

If  crystallised,  the  determination  is  greatly  facilitated, 
but  if  the  crystallisation  is  not  evident,  the  hardness  will 
be  found  a  sufficiently  near  indication  in  the  following 
scheme.  The  requisites  in  determining  the  hardness  of 
gems  are  good  specimens  of  sapphire,  topaz,  and  quartz 
possessing  smooth  bright  surfaces,  as  well  as  sharp  points 
or  corners.  The  hardness  is  determined  by  drawing  the 
sharp  points  of  these  three  test-minerals  over  smooth  bright 
surfaces  of  the  mineral  under  trial.  (See  hardness.)  Or 
it  may  be  ascertained  with  great  certainty  by  means  of  a 
small  angular  fragment,  broken  off  the  mineral  to  be  tried. 
For  convenience  of  holding,  it  should  be  mounted  on  a 
stick  of  sealing-wax,  which  is  best  done  by  previously 
heating  the  fragment,  held  with  a  forceps  over  a  candle 
flame,  and  applying  it,  whilst  hot,  to  the  wax  ;  the  hard- 
ness may  then  be  ascertained  by  drawing  the  fragment 
thus  mounted  across  smooth  surfaces  of  the  sapphire, 
topaz,  and  quartz,  and  observing  whether  a  scratch  is 
thus  produced.  In  this  way  the  hardness  of  a  mineral  not 
larger  than  a  grain  of  sand  may  be  determined. 

The  facility  of  cleavage  is  an  important  character  in 
the  topaz  and  the  diamond. 

The  electrical  properties  are  characteristic  in  the  dia- 
mond, topaz,  and  tourmaline. 

The  specific  gravity  is  a  most  important  aid  in  distin- 
guishing gems,  but  it  cannot  be  attempted  with  an  ordinary 
pair  of  grain  scales  in  the  case  of  minerals  weighing  under 
ten  grains,  at  the  very  least. 

Many  varieties  of  zircon  and  spinel,  and  in  some  cases 
the  topaz  and  emerald,  can  readily  be  distinguished  by  the 


28&  DETERMINATION   OF   MINERALS 

effect  of  heat,  which  is  applied  most  conveniently  by  the 
blowpipe. 

The  diamond  may  be  easily  distinguished  by  the  use  of 
a  small  writing  or  scratching  diamond,  which  fails  to  mark 
the  faces  of  a  real  diamond  when  drawn  lightly  across,  but 
scratches  all  other  gems  with  facility.  After  practice,  the 
sound  caused  by  tapping  two  diamonds  together  becomes 
characteristic. 

1.  CRYSTALLISED  IN  PRISMS. 

HARDNESS. 

7*0.  Six-sided  prisms  or  pyramids ;  sides  of  prism 
finely  marked  across.  No  cleavage.  Frac- 
ture conchoidal.  Infusible.  When  two 
pieces  are  rubbed  together  in  the  dark, 
they  emit  a  phosphorescent  light  and  a 
peculiar  odour.  Specific  gravity,  2*5  to  2 -8. 
Quartz,  1. 

7*0  to  8*0.  Prisms,  three,  six,  nine,  or  more  sided  ;  fur- 
rowed lengthwise.  Black  or  coloured. 
Opaque  or  transparent.  Smooth  sides  of 
prisms  become  electric  by  friction.  No 
cleavage.  Infusible  or  nearly  so.  Specific 
gravity,  3*0  to  3*3.  Tourmaline,  8. 
7 '5.  Prisms,  four-sided,  not  furrowed.  Wine-red, 
brown,  or  white.  Decolorised  permanently 
by  heat.  Adamantine  cleavage,  but  rather 
difficult  to  obtain.  Infusible.  Specific 
gravity,  4  to  5.  Zircon,  12. 

7  to  8.  Prisms,  six  or  more  sided.  Green  usually. 
Imperfect  cleavage.  Fusible  with  difficulty 
in  thin  edges  ;  becoming  clouded  by  heat. 
Specific  gravity,  2- 7  ;  its  low  specific  gravity 
combined  with  its  hardness  is  characteristic. 
Beryl  or  Emerald,  11. 

7 '5  to  8.  Sides  of  prisms  often  finely  marked  lengthwise. 
Cleavage  across  the  prisms  brilliant  and 
easily  obtained.  Smooth  surfaces  become 
strongly  electric  by  friction.  Infusible,  but 
sometimes  blistered  and  altered  in  colour  by 
heat.  Specific  gravity,  3*5,  Topaz,  10. 


BEFORE   THE   BLOWPIPE.  289 

HARDNESS. 

8'5.  Prisms  or  tables.  Green.  Infusible  and  un- 
altered by  heat.  Specific  gravity,  3*5  to  3-8. 
Chrysoberyl,  18. 

9*0.  Prisms,  six-sided  or  irregular.  Cleavage  across 
the  prisms,  but  difficult  to  obtain.  Fracture 
irregular.  Blue,  green,  black,  red,  yellow, 
brown,  or  white.  Infusible.  Easily  distin- 
guished by  its  great  hardness,  scratching 
all  other  gems  except  diamond.  Specific 
gravity,  3- 9  to  4-2.  Sapphire,  ruby,  or  co- 
rundum, 16. 

2.  CRYSTALLISED  IN  OCTAHEDRONS  OR  DODECAHEDRONS. 

HARDNESS. 

7*5.  See  characters  above.  Zircon,  12. 
6-5  to  7'5.  Dodecahedrons.  Usually  red.  Most  varieties 
are  easily  fusible ;  red  infusible,  varieties 
impart  a  green  colour  (due  to  chromium) 
to  borax  bead.  Specific  gravity,  3'1  to  4- 3. 
Garnet,  9. 

8-0.  Octahedrons.  Usually  red  or  black,  also  bluer 
green,  yellow,  and  brown  Some  red  varie- 
ties become  opaque  and  black  when  heated  ; 
rose-red  varieties  become  green  when  heated,, 
but  regain  their  original  colour  on  cooling. 
Specific  gravity,  3'5  to  4*0.  Spinel,  17. 
1OO.  Octahedrons,  dodecahedrons,  or  modifications 
of  these  forms.  Crystalline  facets  often 
curved.  Cleavage  perfect.  '  Lustre,  brilliant 
adamantine.  Usually  colourless,  or  straw- 
coloured.  Not  water-worn.  Strongly  elec- 
tric by  the  slightest  friction.  Specific  gravity, 
3-5.  Diamond,  19. 

N.B. — Before  determining  the  same  of  a  mineral,  it  is  neces- 
sary to  compare  it  with  the  description  to  which  the  number 
refers. 

For  further  particulars  respecting  gems  and  precious 
stones  see  the  concluding  chapter  of  this  volume. 

u 


290 


COLOUKED    FLAMES. 


COLOURED  FLAMES. — There  are  a  great  number  of  sub- 
stances best  detected  by  the  colours  they  impart  to  the 
flame  of  the  blowpipe.  Indeed,  so  important  is  this  point 
that  it  has  been  thought  advisable  to  collect  all  the  facts 
known  on  this  subject  into  one  place,  rather  than  scatter 
them  over  -the  work.  These  experiments  are  best  made 
in  a  dark  room,  and  with  a  very  small  flame.* 


BLUE  FLAMES. 


Large  intense  blue 
Pale  clear  blue  . 
Light  blue  .  , 
Blue  ^  yv  . 
Greenish  blue 
Blue  mixed  with  green 


Chloride  of  copper. 

Lead. 

Arsenic. 

Selenium. 

Antimony. 

Bromide  of  copper. 


GREEN   FLAMES. 


Intense  emerald  green  .         . 

Thallium 

Very  dark  green,  feeble 

.     Ammonia. 

Dark  green            .         .         . 

.     Boracic  acid. 

Full  green              .... 

.     Tellurium. 

Full  green             .... 
Emerald  green,  mixed  with  blue   . 
Pale  green             .... 

.     Copper. 
I  Iodide  of  copper. 
|  Bromide  of  copper. 
.     Phosphoric  acid. 

Very  pale  apple  green  . 

.     Baryta. 

Intense  whitish  green   . 

.     Zinc. 

Bluish  green 

.     Binoxide  of  tin. 

YELLOW  FLAME. 

Intense  greenish  yellow 


Soda. 


BED   FLAMES. 


Intense  crimson 
Red  ^  . 
Reddish  purple 
Violet 


Lithia. 
Strontia. 
Lime. 
Potash. 


Chlorine,  combined  with  copper,  gives  an  intense  blue 
flame.  This  phenomenon  may  be  produced  as  follows  : — 
Take  a  piece  of  thin  brass  wire,  and  bend  one  end  of  it 
several  times  upon  itself ;  place  upon  this  some  microcosmic 
salt,  and  fuse  it  until  it  has  acquired  a  green  colour.  Then 
add  to  it  the  substance  suspected  to  contain  chlorine,  and 
place  it  in  the  oxidising  flame,  just  at  the  point  of  the  blue 


*  Griffin's  *  Blowpipe  Analysis/  p.  148. 


COLOURED    FLAMES.  291 

flame ;  if  any  chloride  be  present  a  splendid  blue  colour 
will  be  produced. 

Lead. — The  blue  colour  produced  by  this  metal  is 
readily  obtained.  Fragments  of  a  mineral  must  be  held 
in  the  tongs,  and  powder  may  be  assayed  on  charcoal. 

Arsenic^  in  the  metallic  state,  gives  rise  to  a  light  blue 
flame. 

Selenium  and  Antimony ',  when  treated  in  the  same 
manner,  afford  characteristic  flames. 

Bromine. — If  any  substance  containing  bromine  be 
placed  in  a  bead  of  fused  microcosmic  salt  on  the  brass 
wire,  and  then  in  the  oxidising  flame,  a  bright  blue  flame 
with  emerald  green  edges  will  be  produced. 

Boracic  Acid. — The  following  is  Dr.  Turner's  process 
for  the  detection  of  boracic  acid.  The  substance  is  to  be 
mixed  with  a  flux  composed  1  part  of  fluor-spar  and  4| 
parts  of  potassium  bisulphate.  This  mixture  is  to  be 
made  to  adhere  to  the  moistened  end  of  a  platinum  wire, 
and  held  at  the  point  of  the  blue  flame  ;  at  the  instant  of 
fusion  a  dark  green  flame  will  be  produced.  It  may  also 
be  produced  by  merely  dipping  the  mineral  in  sulphuric 
acid,  and  exposing  it  to  the  blowpipe  blast.  In  case  a 
very  small  quantity  of  boracic  •  acid  is  contained  in  a 
mineral,  the  following  process  may  be  employed  : — The 
substance  must  be  fused  with  potassium  carbonate  on 
charcoal,  moistened  with  a  drop  or  two  of  sulphuric  acid, 
and  then  a  few  drops  of  alcohol ;  the  latter  will  burn 
with  a  green  flame  when  exposed  to  the  flame  of  the 
blowpipe. 

Tellurium. — The  peculiar  flame  given  by  this  metal  is 
produced  by  heating  a  portion  of  its  oxide  on  charcoal  in 
the  reducing  flame. 

Copper. — All  the  compounds  of  copper,  except  those 
in  which  bromine  and  chlorine  enter,  give  a  beautiful 
green  flame.  The  soluble  salts  give  it  per  se,  but  the  in- 
soluble require  moistening  with  sulphuric  acid. 

Iodine  and  Copper. — To  the  bead  of  microcosmic  salt 
on  the  brass  wire  add  any  compound  containing  iodine, 

U  2 


292  COLOURED    FLAMES. 

and  a  bright  green  flame  will  be  produced  when  the  mass 
is  heated  in  the  oxidising  flame. 

Phosphoric  Acid. — The  phosphates,  when  moistened 
with  sulphuric  acid,  give  a  light  green  tint  to  the  outer 
flame. 

Baryta. — The  soluble  salts  of  baryta  give  a  light  green 
colour  to  the  outer  flame  when  moistened  with  water. 

Zinc,  when  exposed  to  the  blowpipe  flame,  burns  with 
an  intense  whitish-green  light. 

Soda. — Any  salt  of  soda,  or  substance  containing  soda, 
being  exposed  to  the  outer  flame,  gives  a  brush  of  intensely 
coloured  flame,  of  a  fine  amber  or  greenish-yellow. 

Water. — Certain  minerals  containing  water  give  a  feeble 
yellowish  tint  to  the  flame. 

Strontia. — All  the  salts  of  this  substance  which  are 
soluble  in  water  give  a  crimson  tint  to  the  flame,  which 
does  not  endure  after  the  substance  is  fused.  Strontium 
carbonate  must  be  moistened  with  hydrochloric  acid,  and 
strontium  sulphate  must  be  reduced  to  a  state  of  sulphide 
by  ignition  with  charcoal ;  it  must  then  be  moistened  with 
hydrochloric  acid,  after  which  treatment  it  will  exhibit 
the  characteristic  flame. 

Lithia. — All  that  has  been  said  of  strontia  applies  to 
lithia,  but  the  coloured  flame  given  by  lithia  is  permanent , 
whilst  that  afforded  by  strontia  is  evanescent. 

Lime  acts  as  strontia. 

Potash,  treated  as  soda,  gives  a  purplish  light.  This 
is,  however,  very  liable  to  be  masked  by  the  intense 
yellow  communicated  by  small  quantities  of  soda,  which 
are  almost  always  present  with  potash. 


293 


CHAPTER 

VOLUMETRIC   ANALYSIS. 

THE  main  feature  of  volumetry  is  not  so  much  analysis  in 
the  proper  sense  of  the  term,  as  the  quantitative  determi- 
nation of  one  principal  constituent  of  a  substance. 

This  determination  is  done  by  means  of  solutions,  con- 
taining a  certain  quantity  of  reagents  in  a  certain  volume, 
which  is  called  a  standard  solution,  the  quantity  used  of 
such  solution  being  measured  by  graduated  tubes  (burettes, 
pipettes,  &c.). 

The  reaction  of  a  volumetric  analysis  can  be  of  three 
different  kinds,  according  to  the  reagent  used  and  to  the 
substance  to  be  determined. 

1.  The  substance  to  be  analysed  being  an  acid  or  a 
base,  it  can  be  saturated  by  a  suitable  standard  solution 
(saturation-analysis,  used  for  acids,  potash,  soda,  &c.). 

2.  The  substance  to  be  assayed  maybe  precipitated  by 
the  standard  solution,  and  the  completion  of  the  process  is 
observed  when  no  further  precipitate  occurs  (precipitation- 
analysis,  e.g.,  Pelouze's  copper  assay,  Gay-Lussac's  silver- 
assay). 

3.  The  substance  to  be  determined  becomes,  by  the 
standard  solution,  either  oxidised  or  reduced,  and  by  the 
performance  of  this  process  certain  colours  will  appear  or 
disappear,  from  which  the  completion  of  the  process  is  to 
be  observed  (oxidation  or  reduction-analysis,  e.g.,  Schwarz's 
copper  assay). 

These  processes  of  volumetric  analysis  are  frequently 
used  in  assaying. 

The  principle  of  volumetric  analysis  may  be  fully  ex- 
plained by  the  following  examples  given  by  Fresenius.* 

*  Fresenius's  *'  Quantitative  Analysis/  fourth  edition,  p.  76. 


294  PRINCIPLES   OF   VOLUMETRIC   ANALYSIS. 

'  Suppose  we  have  prepared  a  solution  of  chloride  of 
sodium  of  such  a  strength  that  100  c.c.  will  exactly  pre- 
cipitate 1  grm.  silver  from  its  solution  in  nitric  acid,  we 
can  use  it  to  estimate  unknown  quantities  of  silver.  Let 
us  imagine,  for  instance,  we  have  an  alloy  of  silver  and 
copper  in  unknown  proportion,  we  dissolve  1  grm.  in  nitric 
acid,  and  add  to  the  solution  our  solution  of  chloride  of 
sodium,  drop  by  drop,  until  the  whole  of  the  silver  is 
thrown  down,  and  an  additional  drop  fails  to  produce  a 
further  precipitate.  The  amount  of  silver  present  may 
now  be  calculated  from  the  amount  of  solution  of  chloride 
of  sodium  used.  Thus,  supposing  we  have  used  80  c.c., 
the  amount  of  silver  present  in  the  alloy  is  80  per  cent. ; 
since,  as  100  c.c.  of  the  solution  of  chloride  of  sodium  will 
throw  down  1  grm.  of  pure  silver  (i.e.,  100  per  cent.),  it 
follows  that  every  c.c.  of  the  chloride  of  sodium  solution 
corresponds  to  1  per  cent,  of  silver. 

6  Another  example.  It  is  well  known  that  iodine  and 
sulphuretted  hydrogen  cannot  exist  together ;  whenever 
these  two  substances  are  brought  in  contact,  decomposi- 
tion immediately  ensues,  the  hydrogen  separating  from  the 
sulphur  and  combining  with  the  iodine  (I-f-HS  =  HI-f  S). 
Hydriodic  acid  exercises  no  action  on  starch-paste,  whereas 
the  least  trace  of  free  iodine  colours  it  blue.  Now,  if  we 
prepare  a  solution  of  iodine  (in  iodide  of  potassium)  con- 
taining in  100  c.c.  0*7470  grm.  iodine,  we  may  with  this 
decompose  exactly  0*1  grm.  sulphuretted  hydrogen  ;  for 
17  :  127  ::  01:  07470. 

'  Let  us  suppose,  then,  we  have  before  us  a  fluid  con- 
taining an  unknown  amount  of  sulphuretted  hydrogen, 
which  it  is  our  intention  to  determine.  We  add  to  it  a 
little  starch-paste,  and  then,  drop  by  drop,  our  solution 
of  iodine,  until  a  persistent  blue  coloration  of  the  fluid 
indicates  the  formation  of  iodide  of  starch,  and  hence  the 
complete  decomposition  of  the  sulphuretted  hydrogen. 
The  amount  of  the  latter  originally  present  in  the  fluid 
may  now  be  readily  calculated  from  the  amount  of  solution 
of  iodine  used.  Say,  for  instance,  we  have  used  50  c.c. 
of  iodine  solution,  the  fluid  contained  originally  0'05  sul- 


PRINCIPLES   OF   VOLUMETRIC   ANALYSIS.  295 

phuretted  hydrogen ;  since,  as  we  have  seen,  100  c.c.  of 
our  iodine  solution  will  decompose  exactly  0*1  grm.  of 
that  body. 

'  Solutions  of  accurately  known  composition  or  strength, 
used  for  the  purposes  of  volumetric  analysis,  are  called 
standard  solutions.  They  may  be  prepared  in  two  ways, 
viz.  (a)  by  dissolving  a  weighed  quantity  of  a  substance 
in  a  definite  volume  of  fluid ;  or  (b)  by  first  preparing  a 
suitably  concentrated  solution  of  the  reagent  required, 
and  then  determining  its  exact  strength  by  a  series  of 
experiments  made  with  it  upon  weighed  quantities  of  the 
body  for  the  determination  of  which  it  is  intended  to  be 
used. 

*  In  the  preparation  of  standard  solutions  by  method  a, 
a  certain  definite  strength  is  adopted  once  for  all,  which  is 
usually  based  upon  the  principle  of  an  exact  correspon- 
dence between  the  number  of  grammes  of  the  reagent 
contained  in  a  litre  of  the  fluid,  and  the  equivalent  number 
of  the  reagent  (H=l).  In  the  case  of  standard  solutions 
prepared  by  method  b,  this  may  also  be  easily  done,  by 
diluting  to  the  required  degree  the  still  somewhat  too 
concentrated  solution,  after  having  accurately  determined 
its  strength  ;  however,  as  a  rule,  this  latter  process  is  only 
resorted  to  in  technical  analyses,  where  it  is  desirable  to 
avoid  all  calculation.  Fluids  which  contain  the  equivalent 
number  of  grammes  of  a  substance  in  1  litre  are  called 
normal  solutions  ;  those  which  contain  y1^  of  this  quantity, 
decinormal  solutions. 

'  The  determination  of  a  standard  solution  intended  to 
be  used  for  volumetric  analysis  is  obviously  a  most  im- 
portant operation  ;  since  any  error  in  this  will,  of  course, 
necessarily  falsify  every  analysis  made  with  it.  In  scien- 
tific and  accurate  researches  it  is,  therefore,  always  ad- 
visable, whenever  practicable,  to  examine  the  standard 
solution — no  matter  whether  prepared  by  method  a  or 
by  method  b,  with  subsequent  dilution  to  the  required 
degree — by  experimenting  with  it  upon  accurately  weighed 
quantities  of  the  body  for  the  determination  of  which  it  is 
to  be  used. 


290  PRINCIPLES   OF   VOLUMETRIC   ANALYSIS. 

4  In  the  previous  remarks  no  difference  has  been  made 
between  fluids  of  known  composition  and  those  of  known 
power  ;  and  this  has  hitherto  been  usual.  But  by  accept- 
ing the  two  expressions  as  synonymous,  we  take  for  granted 
that  a  fluid  exercises  a  chemical  action  exactly  correspond- 
ing to  the  amount  of  dissolved  substance  it  contains  ;  that, 
for  instance,  a  solution  of  chloride  of  sodium  containing  1 
eq.  NaCl  will  precipitate  exactly  1  eq.  silver.  This  pre- 
sumption, however,  is  very  often  not  absolutely  correct. 
In  such  cases,  of  course,  it  is  not  merely  advisable,  but  even 
absolutely  necessary,  to  determine  the  strength  of  the  fluid 
by  experiment,  although  the  amount  of  the  reagent  it 
contains  may  be  exactly  known,  for  the  power  of  the  fluid 
can  be  inferred  from  its  composition  only  approximately, 
and  not  with  perfect  exactness.  If  a  standard  solution 
keeps  unaltered,  this  is  a  great  advantage,  as  it  dispenses 
with  the  necessity  of  determining  its  strength  before  every 
fresh  analysis. 

'  That  particular  change  in  the  fluid  operated  upon  by 
means  of  a  standard  solution,  which  marks  the  completion 
of  the  intended  decomposition,  is  termed  the  FINAL  REACTION. 
This  consists  either  in  a  change  of  colour ',  as  is  the  case 
when  a  solution  of  permanganate  of  potash  acts  upon  an 
acidified  solution  of  protoxide  of  iron,  or  a  solution  of 
iodine  upon  a  solution  of  sulphuretted  hydrogen  mixed 
with  starch-paste  ;  or  in  the  cessation  of  the  formation  of  a 
precipitate  upon  further  addition  of  the  standard  solution, 
as  is  the  case  when  a  standard  solution  of  chloride  of  sodium 
is  used  to  precipitate  silver  from  its  solution  in  nitric  acid ; 
or  in  incipient  precipitation,  as  is  the  case  when  a  standard 
solution  of  silver  is  added  to  a  solution  of  hydrocyanic 
acid  mixed  with  an  alkali ;  or  in  a  change  in  the  action  of 
the  examined  fluid  upon  a  particular  reagent,  as  is  the  case 
when  a  solution  of  arsenite  of  soda  is  added,  drop  by  drop, 
to  a  solution  of  chloride  of  lime,  until  the  mixture  no  longer 
imparts  a  blue  tint  to  paper  moistened  with  iodide  of  potas- 
sium and  starch-paste,  &c.' 

The  only  condition  on  which  the  volumetric  system  of 
analysis  can  be  carried  on  successfully  is,  that  the  greatest 


APPARATUS   FOR   VOLUMETRIC   ANALYSIS.  297 

care  is  exercised  with  respect  to  the  graduation  of  the 
measuring  instruments,  and  the  strength  and  purity  of  the 
standard  solutions.  A  very  slight  error  in  the  analytical 
process  becomes  considerably  magnified  when  calculated 
for  pounds,  hundredweights,  or  tons  of  the  substance 
tested.  The  end  of  the  operation  in  this  method  of  analysis 
is  in  all  cases  made  apparent  to  the  eye.  (Sutton.) 

We  will  only  speak  here  of  the  preparation  of  potas- 
sium permanganate,  and  will  give  the  preparation  of  other 
solutions  when  describing  the  processes  for  which  they  are 
used. 

STANDARD    SOLUTIONS. 

A  very  useful  form  of  bottle  for  their  preservation  is 
the  ordinary  wash-bottle,  o*  any  common  bottle  fitted  with 
the  same  arrangement  of  tubes.  The  mouth  end  of  the 
blowing  tube  should  be  furnished  with  a  tightly-fitting 
india-rubber  cap  to  prevent  alteration  of  the  standard  by 
evaporation.  A  similar  cap  over  the  point  will  be  useful, 
although  not  absolutely  necessary,  or  it  may  be  closed  by 
a  small  cork  fitting  over  it.  Burettes  can  then  be  filled 
with  the  solution  without  its  frothing,  and  as  the  tube 
which  enters  the  liquid  does  not  reach  the  bottom  of  the 
bottle,  the  sediment,  if  any,  is  not  disturbed  ;  another  ad- 
vantage is,  that  the  solution  does  not  come  into  contact 
with  the  cork,  nor  can  any  dust  enter. 

The  Instruments  and  Apparatus. 

The  Burette — or  graduated  tube  for  delivering  the  stan- 
dard solution — may  be  obtained  in  a  great  many  forms 
under  the  names  of  their  respective  inventors,  such  as  Mohr, 
Gay-Lussac,  Binks,  &c.,  but  as  some  of  these  possess  a  de- 
cided superiority  over  others,  it  is  not  quite  a  matter  of  in- 
difference which  is  used,  and  therefore  a  slight  description 
of  them  may  not  be  out  of  place  here.  The  burette,  with 
india-rubber  tube  and  clip,  contrived  by  Dr.  Frederic  Mohr 
of  Coblentz,  shown  in  Figs.  83  and  84,  has  the  preference 
above  all  others  for  general  purposes. 


298 


APPARATUS   FOE   VOLUMETEIC   ANALYSIS. 


The  advantages  possessed  by  this  instrument  are,  that 
its  constant  upright  position  enables  the  operator  at  once 
to  read  off  the  number  of  degrees  of  test  solution  used  for 
any  analysis.  The  quantity  of  fluid  to  be  delivered  can 
be  regulated  to  the  greatest  nicety  by  the  pressure  of  the 
thumb  and  finger  on  the  spring  clip,  and  the  instrument 


FIG.  83. 


FIG.  84. 


not  being  held  in  the  hand,  there  is  no  chance  of  increas- 
ing the  bulk  of  the  fluid  by  the  heat  of  the  body,  and  thus 
leading  to  incorrect  measurement,  as  is  the  case  with  Binks' 
or  Gay-Lussac's  form  of  instrument.  The  principal  disad- 
vantage of  these  two  latter  forms  of  burette  is,  that  a  correct 


THE   BUKETTE. 


299 


FIG.  85. 


FIG.  86. 


reading  can  only  be  obtained  by  placing  them  in  an  up- 
right position,  and  allowing  the  fluid  to  find  its  perfect  leveL 
The  preference  should,  therefore,  unhesitatingly  be  given  to 
Dr.  Mohr's  burette,  wherever  it  can  be  used ;  the  greatest 
drawback  to  it  is,  that  it  cannot  be  used  for  potassium 
permanganate,  in  consequence  of  its  india-rubber  tube, 
which  decomposes  the  solution. 

We  are  again  indebted  to  Dr.  Mohr  for  another  form 
of  instrument  to  overcome  this  difficulty,  viz.,  the  foot 
burette,  with  india-rubber 
ball,  shown  in  Fig.  85. 

The  flow  of  liquid  from 
the  exit  tube  can  be  regu- 
lated to  a  great  nicety  by 
pressure  upon  the  elastic 
ball,  which  is  of  the  ordi- 
nary kind  sold  for  children, 
and  has  two  openings,  one 
cemented  to  the  tube  with 
shellac,  and  the  other  at  the 
side,  over  which  the  thumb 
is  placed  when  pressed,  and 
on  the  removal  of  which  it 
refills  itself  with  air. 

Gay-Lussac's  burette, 
supported  in  a  wooden 
foot,  may  be  used  instead 
of  the  above  form,  by  in- 
serting a  good  fitting  cork 
into  the  open  end,  through 

which  a  small  tube  bent  at  right  angles  is  passed.  If  the 
burette  is  held  in  the  right  hand,  slightly  inclined  towards 
the  beaker  or  flask  into  which  the  fluid  is  to  be  measured, 
and  the  mouth  applied  to  the  tube,  any  portion  of  the  solu- 
tion may  be  emptied  out  by  the  pressure  of  the  breath,  and 
the  disadvantage  of  holding  the  instrument  in  an  horizontal 
position,  to  the  great  danger  of  spilling  the  contents,  is 
avoided ;  at  the  same  time  the  beaker  or  flask  can  be  held 
in  the  left  hand  and  shaken  so  as  to  mix  the  fluids,  and  by 


300 


THE    BURETTE. 


FIG.  87. 


FIG.  88. 


this  means  the  end  of  the  operation  is  more  accurately 

determined. 

Fig.  86  will  show  the  arrangement  here  described. 
Mr.  J.  Blodget  Britton  has  described,  in  the  '  Chemical 

News '  for  August  5, 1870,  a  burette  for  use  in  determining 

iron  in  metals  and  ores. 

Figures  87  and  88  represent  two  of  the  kind,  but  of 

different  patterns,  mounted   on  walnut-wood  stands  ;  the 

former  is  for  metals,  and 
the  latter,  of  smaller  capa- 
city, for  ores. 

Securely  fastened  to  the 
upright,  B,  is  a  graduated 
tube,  A,  having  its  lower 
part  drawn  out  in  the 
usual  manner,  but  bent 
outwards  at  an  angle  of 
about  25°.  E  is  a  piece  of 
cork  riveted  into  a  sheet- 
steel  spring,  D,  which  presses 
tightly,  by  means  of  the 
latter,  against  the  vent  of 
the  tube,  c  is  a  thumb- 
screw passing  through  the 
frame  and  bearing  against 
the  spring. 

The  tube  of  Fig.  88  has 
a  capacity  of  100  c.c.  and 
is  graduated  into  tenths,  or 
1000° ;  but  that  of  Fig.  87 
has  a  capacity  of  150  c.c. 
and  is  graduated  into  20ths, 

though  only  at  its  lower  and  narrow  part. 

Modes    of    operating. — Place  a   small   narrow-necked 

funnel  in  the  tube,  as  shown  by  the  figures ;  pour  in  the 

solution  to  be  used  until  it  quite  reaches  the  funnel,  and 

then  remove  the  latter  to  carry  away  any  floating  bubbles  ; 

turn  the  thumbscrew  and  bring  the  top  line  of  the  solution 


THE    PIPETTE. 


301 


FIG.  89. 


50CC 


exactly  to  the  0  line  of  the  scale  ;  stop  the  flow,  and  after- 
wards touch  the  point  of  the  cork  with  a  glass  rod  to  take 
from  it  any  adhering  drop.  The  instrument  is  then  ready 
for  use.  By  means  of  the  thumbscrew  the  dropping  may  be 
controlled  with  extreme  nicety  or  instantly  stopped.  Cork, 
after  a  little  use,  becomes  quite  inert  towards  potassium 
permanganate.  The  occasional  application  of  some  pure 
tallow  to  the  end  of  the  tube  and  cork  will  be  quite  effectual 
in  preventing  any  of  the  fluid  from 
running  upwards  by  capillary  at- 
traction. 

For  everyday  use  in  the  labo- 
ratory, as  well  as  for  very  accurate 
determinations,  this  burette  will 
find  favour. 

The  Pipette. — The  pipettes  used 
in  volumetric  analysis  are  of  two 
kinds,  viz.,  those  which  deliver 
one  certain  quantity  only,  and 
those  which  are  graduated  so  as 
to  deliver  various  quantities  at  the 
discretion  of  the  analyst.  In  the 
former  kind,  or  whole  pipette,  the 
graduation  may  be  of  three  kinds, 
namely,  1st,  in  which  the  fluid  is 
suffered  to  run  out  by  its  own 
momentum  only.  2nd,  in  which 
it  is  blown  out  by  the  breath. 
3rd,  in  which  it  is  allowed  to  run 
out  to  a  definite  mark.  Of  these 
methods  the  last  is  preferable  in 
point  of  accuracy,  and  should 
therefore  be  adopted  if  possible. 
The  next  best  form  is  that  in 
which  the  liquid  flows  out  by  its 
own  momentum,  but  in  this  case 

the  last  few  drops  empty  themselves  very  slowly ;  but  if 
the  lower  end  of  the  pipette  be  touched  against  the  beaker 


10CC 


302  COLOEIMETRIC   ANALYSIS. 

or  other  vessel  into  which  the  fluid  is  poured,  the  flow  is 
hastened  considerably,  and  in  graduating  the  pipette,  it  is 
preferable  to  do  it  on  this  plan. 

In  both  the  whole  and  graduated  pipettes,  the  upper 
end  is  narrowed  to  about  -|-inch,  so  that  the  pressure  of 
the  moistened  finger  is  sufficient  to  arrest  the  flow  at  any 
point. 

Fig.  89  shows  two  whole  pipettes,  one  of  small  and  the 
other  of  large  capacity,  and  also  a  graduated  pipette  of 
medium  size. 

The  Measuring  Flasks. — These  indispensable  instru- 
ments are  made  of  various  capacities ;  they  serve  to  mix 
up  standard  solutions  to  a  given  volume,  and  also  for  the 
subdivision  of  the  substance  to  be  tested  by  means  of  the 
pipettes,  and  are  in  many  ways  most  convenient.  They 
should  be  tolerably  wide  at  the  mouth,  and  have  a  well- 
ground  glass  stopper,  and  the  graduation  line  should  fall 
just  below  the  middle  of  the  neck,  so  as  to  allow  room  for 
shaking  up  the  fluid. 

Colorimetric  Analysis  is  also  used  in  assaying.  It  is 
based  upon  the  fact  that  a  coloured  solution  appears  the 
more  intense  the  more  of  the  colouring  substance  it  con- 
tains. 

If,  therefore,  a  solution  containing  a  certain  amount  of 
a  substance  and  being  in  consequence  of  a  certain  intensity 
of  colour,  is  prepared,  it  will  be  possible  to  obtain  the  solu- 
tion under  assay  of  an  equal  intensity  of  colour  by  appro- 
priate dilution. 

By  measuring  the  volume  of  the  assay  solution  and 
taking  into  consideration  the  amount  of  the  standard  solu- 
tion, the  quantity  of  the  substance  contained  in  the  assay 
solution  may  be  readily  calculated. 


303 


CHAPTER  IX. 

THE   ASSAY   OF  IRON. 

THE  ores  of  iron,  properly  so  called,  always  contain  the 
metal  in  the  oxidised  state,  and  in  various  degrees  of 
purity. 

The  oxides  and  carbonates  are  the  only  minerals  of 
iron  which  can  be  used  as  ores  in  the  blast-furnace.  These 
are  associated  with  different  impurities  or  foreign  materials 
in  greater  or  less  proportion.  The  following  is  a  list  of  the 
principal  ores  of  iron,  with  the  maximum  percentage  of 
metallic  iron  that  could  occur  in  each,  if  it  were  absolutely 
pure,  as  in  its  formula  : — 

MAGNETIC  IRON  OBE,  Fe304=Fe203  +  FeO,  7241. 

RED  HEMATITE  and  specular  ore  (anhydrous  iron,  ses- 
quioxide  or  ferric  oxide),  Fe203,  70*00. 

BROWN  HEMATITE,  limonite  (brown  iron  ore),  2Fe.203,3H20, 
59-92. 

SPATHIC  IRON  ORE  (iron  carbonate),  FeO,C02,  48-22. 

TITANIFEROUS  ORE  (ilmenite),  FeO,Ti02,  +  nFe203,  36-82. 

FRANKLINITE,  3(FeO,ZnO,MnO)  +  (Fe203,Mn203),  45-16. 

Besides  these  may  be  mentioned  the  varieties  of  impure 
iron  carbonates,  known  as  clay  or  clay-band  ironstone  and 
black-band  ironstone.  Clay-band  ironstone  sometimes  re- 
sembles compact  limestone,  sometimes  greyish  hardened 
clay.  Its  great  specific  gravity,  its  effervescing  on  the  addi- 
tion of  an  acid,  and  acquiring  a  brown-red  colour  on  roast- 
ing, are  sufficient  means  of  identifying  it. 

The  following  is  the  result  of  an  analysis  of  this  class 
of  ore  by  the  Author ;  the  specimen  was  from  Ireland, 
county  Leitrim : — 


304 


THE   ASSAY   OF   IRON. 


Ferrous  oxide 

Ferric  oxide     . 

Manganese  oxide 

Alumina 

Magnesia 

Lime 

Potash     . 

Soda 

Sulphur    . 

Phosphoric  acid 

Carbonic  acid 

Silica 

Carbonaceous  matter  and 


loss 


51-653 

3-742 

•976 

1-849 

•284 

•410 

•274 

•372 

•214 

•284 

31-142 

6-640 

2-160 

100-000 


Black-band  is  a  combustible  schistose  variety  of  this  ore. 
The  following  analysis  is  also  by  the  Author  : — 


Ferrous  oxide 
Ferric  oxide     . 
Manganese  oxide 
Alumina 


Lime 

Potash 

Soda 

Phosphoric  acid 

Silica       . 

Sulphur 

Carbonic  acid 

Carbonaceous  matter 

Water  and  loss 


20-924 

•741 

1-742 

14-974 

•987 
•881 

traces 

•114 
26-179 

•098 

14-000 

16-940 

2-420 

100-000 


Besides  these  iron  ores  the  following  substances,  con- 
taining iron  and  used  as  fluxes,  require  assaying  :  Granite, 
Chlorite,  Basalt,  Pyroxene,  Amphibole,  and  also  some  kind 
of  slags  (finery  cinder,  tap  cinder,  &c.). 

A.    THE   ASSAY   OF   IRON   IN  THE   DRY  WAY. 

Iron  ores  very  seldom  occur  in  a  pure  state,  and  the 
ores  may  be  arranged  for  their  assay  in  the  dry  way  (and 
also  for  smelting)  into  five  classes. 

1.  Iron  ores  containing  silica,  lime,  and  another  base, 

which  ores  are  fusible  per  se. 

2.  Iron  ores  containing  predominantly  silica. 

3.  „         „         „  „  lime. 

4.  „  „  alumina. 


THE   ASSAY   OF   IRON    IX   THE   DKY   WAY. 


305 


5.  Iron  ores  containing  a  large  amount  of  magnesia  ; 
these  ores  are  most  difficultly  rendered  fluid. 

The  flux  used  for  assaying  (and  also  melting)  varies 
according  to  the  nature  of  the  predominant  compound,  and 
the  quantity  used  according  to  the  amount  of  that  com- 
pound. 

If  the  composition  of  the  ore  is  known,  it  is  easy  to 
ascertain  the  amount  of  flux  necessary  to  form  a  slag  w^ith 
the  bases  or  silica  present ;  in  most  cases  an  extra  quantity 
of  the  flux  should  be  added,  in  order  to  produce  a  sufficient 
volume  of  slag  to  cover  the  button. 

According  to  Dr.  Percy,*  blast-furnace  cinder  of  the 
following  formula  may  be  taken  as  a  type  of  the  kind  of 
slag  desirable  :— 

Al203,Si03  2(3CaO,Si03). 

Its  approximate  composition  per  cent,  is  as  under  : — 

Silica          ....        381  f  2^  parts 


Alumina 
Lime 


or  about J  I/ 
\3 


The  following  mixtures  of  various  fluxes,  when  fused, 
produce  a  slag  which  may  be  regarded  as  approximating 
to  the  above  composition  :  — 


China  Clay      .     2 

Silica     .     .     0-92  f 
Alumina     .     0'82 

1-92 
2-5 

Silica 

1-751 

Glass      .     .     .     2£< 
Lime       ...     2^ 

Materials  =  Alumina 

tO-75 
2-5 

i  g;j:ca 

1-81 

Shale  or  fire-clay  3 

Alumina 

.      0-9 

Lime                      2A 

2-5 

"  36-5  per  cent. 

15-5 

)) 

48-0 

>i 

35 

>» 

15 

50 

» 

35 

)t 

17 

» 

48 

According  to  Bodemann  a  compound  of  56%  silica, 
30%  lime,  and  14%  alumina  forms  a  slag  most  easily  ren- 
dered fluid,  but  as  it  is  found  that  this  slag  itself  is  not 
sufficiently  fusible  in  a  small  assaying  furnace  (air-furnace), 
an  addition  of  fluor-spar  is  made  to  the  mixture,  and  in 
some  cases  (the  iron  ore  being  very  difficultly  rendered 

1  Percy's  Metallurgy,  p.  240. 

2  30°/0  say  of  alkalies,  lime,  &c.,  on  account  of  their  fusibility,  are  taken  as 
equivalent  to  so  much  alumina. 


300  THE   ASSAY    OF   IRON   IN    THE   DRY   WAY. 

fluid)  some  borax  is  added,  or  a  mixture  of  borax  and  fluor- 
spar. 

An  exact  knowledge  of  the  mineral ogical  properties 
of  the  iron  ores,  and  a  due  experience,  will  enable  the 
assayer  to  properly  adjust  the  fluxes  without  resorting  to 
an  analysis  to  find  what  amount  of  silica  and  bases  are 
present. 

In  some  iron  works  of  Germany  the  following  propor- 
tions of  fluxes  are  used  : — 

For  magnetic  ore,  red  haematite  )    5  to  20°/0     chalk   and  250/0  fluor-spar 

(very  rich)        .         .          [ 

„    argillaceous  brown  iron  ore     20  to  40  „        „          „  30  to  40  „         „ 
„    bog  iron  ore        .         .        >'"*           50  „     _  „          „  50  „         „ 

„    spathose  iron  ore        .         .     10  to- 15  „  china  clay  ,,  20  to  25  ,,         „ 

„    finery  cinder      .         .         .     20  to  25  „    chalk       „  20  to  25 „        „ 

Air-furnaces  are  best  adapted  for  assaying  iron  ores 
where  many  assays  are  required. 

The  furnace  should  have  a  cross  section  of  18  in.  x  18 
in.,  and  depth  to  grate-bars  21  inches.  Flue  7  in.  x  7  in. 
Anthracite  is  the  best  fuel  to  use  ;  then  coke. 

In  the  assay  of  an  iron  ore  it  is  required  to  reduce  the 
oxide  of  iron  to  the  metallic  state,  or  rather  that  of  cast- 
iron,  to  collect  in  a  button,  and  to  form  writh  the  foreign 
materials  of  the  ore — by  means  of  fluxes — a  fusible  slag 
that  will  not  retain  any  of  the  iron,  in  combination,  or  in 
the  form  of  pellets. 

Naked  crucibles,  either  of  clay  or  blacklead,  or  cruci- 
bles lined  with  charcoal,  are  employed  ;  the  latter  are 
preferable.  The  button  of  metal  does  not  adhere  to  naked 
pots,  but  the  slag  adheres  very  strongly  ;  so  much  so,  that 
it  cannot  be  detached  with  any  degree  of  accuracy  for 
weighing  (which  in  some  of  M.  Berthier's  processes  is  of 
importance).  Blacklead  pots  allow  neither  the  slag  nor 
button  to  adhere,  but  the  former  dissolves  much  argilla- 
ceous matter  from  the  pot,  so  that  its  weight  is  greatly 
increased,  and  the  assay  cannot  be  verified.  In  naked 
crucibles,  charcoal  must  always  be  added  to  the  assay,  to 
reduce  the  iron  oxide  ;  in  which  case,  if  an  excess  be  added, 
it  prevents  the  button  from  completely  forming,  so  that 


THE   ASSAY    OF   IROX    IX   THE   DRY   WAY.  307 

globules  remain  in  the  slag  (with  care  this  may,  however, 
be  avoided).  Neither  do  naked  crucibles  resist  the  fire  as 
well  as  those  lined  with  charcoal,  because  the  lining  sup- 
ports the  sides  when  they  soften.  The  charcoal  lining  also 
allows  the  assay  to  be  finished  without  adding  any  reagent 
to  the  ore  ;  the  button  can  be  readily  taken  out,  because 
it  does  not  adhere  to  the  charcoal ;  and  lastly,  the  earthy 
matters  in  the  ore,  which  have  formed  a  slag,  may  be  col- 
lected and  weighed.  If  we  have  added  any  flux  to  the  ore, 
the  total  weight  can  also  be  ascertained. 

The  method  of  lining  crucibles  with  charcoal  brasque 
and  conducting  the  assay  is  given  as  follows  by  Mr. 
Blossom :  * 

The  brasque  has  a  composition  of  four  parts  of  finely- 
pulverised  charcoal  to  one  part  of  molasses.  This  must 
be  thoroughly  kneaded  until  a  ball  of  it  made  in  the  hands 
resists,  to  a  sensible  degree,  an  attempt  to .  pull  it  apart. 
The  crucibles  are  packed  full  by  driving  the  brasque  in 
with  a  mallet ;  a  conical  cavity,  of  sufficient  size  for  the 
charge,  is  then  cut  out,  and  the  brasque  dried  in  an  oven. 
Care  must  be  taken  not  to  burn  the  molasses,  for  the  brasque 
would  in  that  case  crumble,  and  be  useless. 

These  are  the  best  crucibles  for  iron  assays,  because 
they  combine  the  following  advantages  : — 

Being  lined  with  charcoal,  none  need  be  mixed  with 
the  charge  to  reduce  the  oxide,  whereas  in  naked  crucibles 
charcoal  must  be  added,  and  is  liable  to  prevent  the  com- 
plete collection  of  the  iron  in  a  button  by  holding  little 
pellets  in  suspension. 

The  slag  neither  adheres  to  a  charcoal  lining  nor  takes 
up  any  material  from  it,  while  it  does  adhere  to  ordinary 
naked  crucibles,  and  dissolves  argillaceous  matter  from 
blacklead  crucibles.  In  the  former  case,  then,  the  slag 
may  be  weighed  as  a  verification  of  the  assay,  while  in  the 
latter  this  is.  of  course,  impossible. 

The  lining  serves  as  a  support  for  the  crucible,  which, 
under  the  high  heat  employed,  is  very  apt  to  be  softened 
and  crushed  beneath  the  weight  of  the  fuel. 

*   CJiemical  Neics,  April  5,  1872. 
x  2 


308  THE   ASSAY   OF   IRON   IN   THE   DRY    WAY. 


The  Charge. 

In  making  up  the  charge  it  is  only  necessary  to  con- 
sider the  materials  required  as  fluxes  for  the  foreign 
matters  of  the  ores.  It  may  be  well  to  sprinkle  a  little 
charcoal  into  the  charge  as  a  precaution,  but  none  is  abso- 
lutely required.  Two  cases  may  arise,  in  which  we  have 
(1)  ores  of  unknown  composition,  and  (2)  ores  previously 
analysed.  The  assay  in  both  cases  gives  us  a  clue  to  the 
nature  of  the  iron  that  may  be  obtained  from  the  ore,  and 
to  the  character  and  proportion  of  the  fluxes  to  be  added  in 
the  blast-furnace,  in  order  that  we  may  produce  a  fusible 
slag  free  from  iron.  In  the  former  case,  we  obtain  the 
additional  information  of  the  approximate  percentage  of 
iron,  though  the  iron  assay  is  seldom,  if  ever,  made  for 
this  purpose.  Eecourse  is  had  to  the  more  accurate 
chemical  analysis,  which  gives  us  the  exact  proportions  of 
the  substances  which  affect  the  iron  injuriously  or  other- 
wise. In  all  the  assays  a  constant  weight  of  ore,  10 
grammes,  is  taken. 

1.  Ores  of  Unknown  Composition. 

In  the  assay  of  an  ore  the  composition  of  which  is 
unknown,  we  employ  one  or  more  preliminary  assays, 
and,  if  satisfactory  results  be  not  obtained  from  either, 
we  make  another  assay  with  a  charge  modified  according 
to  the  indications  of  the  preliminary  assay.  The  follow- 
ing charge  may  be  used  to  advantage  in  the  preliminary 
assay  : — 

Preliminary  Assay — Charges. 

I.  ii.  ni.  IV. 

Silica        .         .        4        .        2-5          1  4'0  2-5—0  grms. 

Lime         ....        2-5          4  1-5  2-5—3      „ 

Ore       <    ^     r        i    -.••',      10-0        10          10-0  10-0  „ 

1.  The  first  charge  is  employed  for  the  purer  ores,  those 
containing  very  little  gangue,  such  as  some  varieties  of 
magnetic  ore,  red  and  brown  hsernatites,  specular  and 
micaceous  ores. 


THE   ASSAY   OF   IRON   IN   THE   DRY  WAY.  309 

•N 

2.  Ores   containing  silica ;    some  varieties    of  brown 
haematite,  magnetic  ore,  &c. 

3.  Ores  containing  lime,  magnesia,  or  protoxide  of  man- 
ganese carbonates,  &c. ;  calcareous  hematites,  spathic  iron. 

4.  Ores  containing  silica  and  alumina  ;  clay  ironstones, 
black-band,  &c. 

The  principle  involved  in  all  the  charges  is  that  of 
furnishing  a  base,  lime ;  for  an  acid,  silica ;  and  vice 
versa. 

The  choice  of  a  charge,  therefore,  depends  on  the 
acid  or  basic  nature  of  the  gangue  of  the  ore.     The  mate- 
rials of  the  gangue  might  possibly  be  associated  in  such 
proportions  as  to  flux  themselves,  but  this  would  happen 
rarely. 

Ores  containing  titanium  require  the  addition  of  fluor- 
spar to  the  charge,  in  quantity  varying  from  0'5  to  10 
grms.,  according  to  the  amount  of  titanium  present. 

2.  Ores  Previously  Analysed. 

When  we  know  the  percentage  composition  of  an  ore, 
it  is  a  very  simple  matter  to  calculate  a  charge  for  the  dry 
assay.  Good  results  are  obtained  from  a  charge  so  propor- 
tioned as  to  yield  a  slag  corresponding  to  the  following 
formula  of  a  blast-furnace  cinder,  as  given  by  Percy  : — 

E203,Si03  +  2(3EO,Si03). 

E203  represents  alumina,  and  EO,  lime,  magnesia,  and  other 
bases.  Its  approximate  percentage  composition  is  as  fol- 
lows : — 

Silica 38]  f  2^  parts 

R203  (alumina)          ....         15  1- or  about-!  1       „ 
RO  (lime,  magnesia,  &c.)  .        .        47  J  1 3      „ 

We  have,  then,  only  to  establish  the  latter  relation 
between  the  component  materials  of  the  gangue,  to  obtain, 
on  fusion,  the  above  slag. 

Let  us  take  the  following  example  : — 

10  grms.  Ore  Difference 

The  Ore  contains         Per  cent.  contains  Required  to  be  added 

Silica  .         .         1-65  0-165  2-50  2'335  grins. 

Alumina      .         1-94  0-194  I'OO  0-806     „ 

Lime,  MgO,  &c.  4-51  0-451  3-00  2-549    „ 


310  THE   ASSAY   OF   IRON   IN   THE   DRY   WAY. 

Silica  is  supplied  by  ground  quartz.  For  the  bases 
EO  represented  in  the  furnace  slag  and  in  the  ore  by  lime, 
magnesia,  &c.,  we  add  pure  unslaked  lime.  The  alumina 
is  added  in  the  form  of  kaolin,  which  may  be  assumed  to 
contain  equal  parts  of  alumina  and  silica.  Allowance  must 
be  made  in  adding  silica  for  that  introduced  with  the 
kaolin. 

It  happens  sometimes  that  the  ore  contains  more  than 
is  required  of  one  of  the  ingredients  of  the  slag,  or  the 
silica  introduced  with  the  kaolin  may,  when  added  to  that 
already  present,  increase  the  quantity  beyond  the  require- 
ment. In  either  case  make  up  a  new  slag  with  the  excess. 
The  following  is  an  example  of  both  cases  : — 

10  grms.  Ore  Difference 

The  Ore  contains         Per  cent.  contains  Required       to  be  added 

Silica  .        .        25-96          2-596  2-50        -0-096 

Alumina      .          6-92          0-692  1-00  0-308 

Lime,  MgO,  &c.     7'59          0-759  3-00  2-241 

Kaolin  (ALO..A,  SiOA)  required  to  furnish  0-308 

A1203     .        .        .        .         .        .          0-616 

Silica  contained  in  0-616  kaolin         .          Q-308         fj 
Silica  in  excess  in  ore        .         .         .  $-096 

Total  excess  of  silica          .       ,.          $404         D 

/ 

Add  fluxes  to  make  up  with  this  excess  more  slag  of 
the  same  composition  as  above. 

Difference 
Excess  Required        to  be  added 

Silica        .        .        .        .        0-404  2-50  2-096 

Alumina   ....  1-00  1-000 

.Lime,  magnesia,  &c.  .         .  3-00  3-000 

Kaolin  required  to  furnish  1-00  A1203  .  .  2-000 
Silica  contained  in  2-00  kaolin  ....  1-000 
Silica  to  be  added,  2-096-1-000  .  .  .  1-096 

Total  material  to  be  added  to  the  charge  : — 

Silica     .  .         ...         .         .         .         1-096 

Kaolin  .        .        0-616 +  2-00       .        .        .        2-616 

Lime     .       *.         .        2-241  +  3-00       .      '.        .         5-241 

The  charge  having  been  weighed  out,  it  must  be  tho- 
roughly mixed  on  glazed  paper ;  after  placing  it  in  the 
crucible,  the  conical  cavity  is  closed  with  a  piece  of  char- 
coal, and  the  whole  top  of  the  crucible  is  covered  with  a 
luting  of  fire-clay.  The  latter  is  mixed  with  ^ — J  part 


THE   ASSAY   OF   IRON   IN   THE   DRY   WAY.  311 

fine  sand,  and  is  made  plastic  with  borax  water.  Hair  is 
sometimes  employed  to  prevent  the  luting  from  cracking 
off  when  dry ;  but  no  trouble  is  experienced  from  this 
source  if  the  luting  be  properly  made  and  applied.  It 
should  not  be  put  on  too  thick,  should  be  lapped  over  the 
edges  of  the  crucible,  and  thoroughly  dried  before  placing 
the  crucible  in  the  furnace. 

Four  crucibles  are  introduced  at  one  time,  and  rest 
upon  two  fire-bricks  placed  one  upon  the  other,  to  keep  the 
crucibles  in  the  very  midst  of  the  glowing  coals.  If  the 
crucibles  do  not  rest  steadily  on  the  bricks,  it  is  well  to 
support  them  with  a  little  luting,  to  prevent  their  being 
knocked  over  in  the  fire.  A  low  fire  may  be  kindled  before 
the  introduction  of  the  crucibles,  or  it  may  be  kindled 
around  them.  The  fuel  is  added  gradually  until  it  fills 
the  furnace  above  the  tops  of  the  crucibles  ;  the  fire  is 
then  maintained  at  its  maximum  temperature  for  2i — 3.^ 
hours,  according  to  the  refractory  nature  of  the  ore.  Ores 
containing  much  titanium  may  even  require  4  hours, 
while  carbonates  containing  manganese  may  fuse  well  in  2^ 
hours,  or  in  less  time.  Three  hours  will  generally  be  suffi- 
cient for  ores  that  do  not  contain  much  titanium.  When 
the  fire  has  burned  out,  the  bricks  and  crucibles  are 
removed  in  one  mass,  cemented  together  by  the  slag  of 
the  fuel.  The  crucibles  are  detached,  and  the  exteriors 
broken  with  a  hammer ;  on  inverting  and  tapping  the 
brasque  lining,  the  slag  and  the  button  of  cast  iron  will 
fall  into  the  hand,  when,  if  they  adhere  together,  a  slight 
tap  will  suffice  to  separate  them.  Before  separation,  how- 
ever, they  should  be  carefully  cleansed  and  weighed  ;  if 
necessary,  the  slag  may  then  be  broken,  and  any  particles 
of  iron  it  retains  mechanically  may  be  extracted  with  a 
magnet.  The  weight  of  the  iron  being  deducted  from  the 
weight  of  the  slag  and  button,  we  obtain  the  weight  of  the 
slag.  This  ought  to  approximate  closely  to  the  weight  of 
the  fluxes  introduced  and  the  corresponding  material  of 
the  ore.  If  a  large  amount  of  iron  has  combined  with  the 
slag  it  will  be  indicated  by  the  excess  in  weight.  Titanium 
and  manganese  enter  the  slag  almost  completely  ;  hence  if 


312  THE   ASSAY    OF    IRON    IX   THE   DRY   WAY. 

they  are  present,  allowance  must  be  made  for  them. 
Duplicate  assays  are  made,  and  the  two  results  should 
not  differ  more  than  0*3 — 0-4  of  one  per  cent.  The  slag 
ought  to  be  well-fused,  colourless,  transparent,  and  vitreous, 
or  white,  light-grey,  bluish-grey,  opaque,  and  semi- vitreous, 
resembling  porcelain  or  enamel. 

A  good  button  will  be  well -formed,  and  will  separate 
completely  from  the  slag. 

If  the  metal,  be  of  good  quality,  the  button,  when 
wrapped  in  a  piece  of  thin  tin  plate,  and  struck  on  the 
anvil,  will  flatten  slightly  before  breaking.  It  ought  to  be 
grey  or  greyish-white,  and  the  grain  fine,  or  tolerably  fine. 
A  button  of  bad  iron  breaks  readily  without  changing 
form,  sometimes  even  pulverising:  the  metal  is  generally 
white  and  crystalline  on  the  surface. 

The  following  are  some  of  the  characters  that  may  be 
observed  in  slags,  and  their  indications  with  reference  to  the 
charge  : — A  perfectly  transparent  slag  of  greenish  tint  in- 
dicates an  excess  of  silica.  A  stony  rough  slag,  or  one  that 
is  crystalline  in  fracture  and  dull  in  lustre,  indicates  an 
excess  of  bases. 

If  the  product,  instead  of  being  melted,  is  only  fritted, 
and  contains  the  reduced  iron  interspersed  as  a  fine  grey 
powder,  both  silica  and  alumina  are  deficient  in  the  flux, 
lime  and  magnesia  being  in  excess.  The  latter  is  one  of 
the  most  refractory  substances  found  in  iron  ores,  and, 
when  present  in  quantity,  requires  an  addition  of  both 
silica  and  lime.  A  vesicular  slag,  with  the  iron  interspersed 
in  malleable  scales,  indicates  the  presence  in  the  ore,  of  iron 
and  manganese  silicates,  or  an  excess  of  silica,  which  react 
on  the  carburetted  iron  as  it  forms,  producing  malleable 
iron  and  carbonic  acid.  This  trouble  is  corrected  by  the 
addition  of  lime. 

Manganese  in  small  quantity  gives  an  amethystine  tint 
to  the  slag ;  in  larger  proportion  it  produces  a  yellow, 
green,  or  brown  colour. 

Titanium  often  produces  a  resinous,  black,  and  scoria- 
ceous  slag,  sometimes  curiously  wrinkled  on  the  outside. 
It  is  covered  on  the  outside  with  a  metallic  pellicle  of  the 


THE   ASSAY    OF   IROX   IN   THE   DRY   WAY.  313 

cyano-nitride  of  titanium  with  its  characteristic  copper 
colour ;  sometimes  the  slag  is  vitreous  and  of  a  bluish  tint. 
Chromium  gives  a  dark  resinous  slag,  sometimes  surrounded 
by  a  thin  metallic  coating. 

The  following  are  some  characters  of  the  button  depen- 
dent on  the  substances  named  :— 

Phosphorus. — A  hard,  brittle,  white  metal,  known  as 
cold-short. 

Sulphur. — A  strong,  reticulated,  mottled  structure,  and 
red-short  iron. 

Manganese. — A  button  smooth  exteriorly,  hard  and 
nongraphitic  :  it  breaks  under  the  hammer  and  presents  a 
white  crystalline  fracture. 

Titanium. — The  button  is  smooth  on  the  outside,  and 
breaks  under  the  hammer  with  a  deep  grey  fracture,  dull 
or  crystalline.  It  adheres  strongly  to  the  slag.  The  button 
is  covered  sometimes  with  titanium  cyano-nitride  with  its 
characteristic  copper  colour.  Titanium  is  said  to  increase 
the  strength  of  the  metal.  It  may  be  present  to  the  extent 
of  one  per  cent. 

Chromium. — Sometimes  the  button  is  smooth,  well- 
fused,  with  a  brilliant  crystalline  fracture  and  tin-white 
colour ;  at  other  times  it  is  white,  only  half-fused,  or  it 
may  even  form  a  spongy  mass  of  a  clear  grey  colour, 
according  to  the  quantity  of  chromium  contained  in  the 
iron.  Many  alloys  of  iron  and  chromium  will  scratch 
glass. 

Berthier  recommends  the  following  method  for  estima- 
ting the  other,  chiefly  slag-forming,  components  of  iron- 
ores.  The  operations  of  this  method  are  comprised  in 
roasting  or  calcining,  to  drive  off  any  volatile  or  combus- 
tible matters,  and  in  treating  the  ore  with  certain  acids, 
the  object  of  which  is  to  ascertain  the  amount  of  insoluble 
matter,  by  difference  of  weight,  before  and  after  the  action 
has  taken  place. 

The  hydrated  ores  are  calcined  to  estimate  water; 
and  those  containing  manganese,  to  reduce  it  to  a  fixed  and 
known  state  of  oxidation  (sesquioxide).  The  carbonates 
are  roasted  to  expel  carbonic  acid,  and  the  ores  from  the 


314  THE   ASSAY   OF    IRON    IN   THE   DRY   WAY. 

coal-formations  to  burn  the  combustible  matter  with  which 
they  are  mixed. 

Slags  and  dross  are  also  roasted  to  free  them  from 
charcoal.  A  simple  calcination  sometimes  is  sufficient,  as  in 
the  case  of  carbonates  ;  but  where  mixtures  of  ferric  and 
ferrous  oxides  are  to  be  assayed,  they  must  be  subjected 
to  a  long  roasting,  in  order  to  convert  all  the  contained 
ferrous  oxide  into  ferric  oxide. 

Diluted  and  cold  nitric  or  acetic  acids  are  employed 
for  minerals  whose  matrix  is  purely  calcareous  or  magne- 
sian,  as  these  acids  dissolve  the  earthy  carbonates,  without 
attacking  either  stones,  clay,  or  the  iron  oxides.  The 
residue  is  to  be  well  washed,  dried,  and  weighed,  and  the 
amount  of  carbonates  calculated  by  the  difference.  It  is 
now  to  be  treated  with  boiling  hydrochloric  acid,  or,  what 
is  preferable,  aqua  regia.  The  ores  which  contain  sub- 
stances insoluble  in  these  acids  are  generally  of  a  clayey  or 
flinty  nature.  These  are  to  be  weighed,  and  according  to 
their  weight  that  of  the  flux  to  be  added  in  the  assay  is 
determined,  as  will  be  shown  hereafter. 

It  must  be  borne  in  mind,  however,  that  the  clays 
are  not  absolutely  insoluble  in  hydrochloric  acid,  for  a 
certain  quantity  of  alumina  is  always  dissolved,  which  is 
generally  greater  in  proportion  to  the  amount  present  in 
the  iron  ore. 

The  ores  containing  titanium  are  boiled  with  concen- 
trated sulphuric  acid,  after  they  have  been  reduced  to  the 
finest  possible  state  of  division.  All  the  iron,  titanium,  and 
manganese  oxides  are  dissolved,  and  the  stony  gangues 
which  resist  the  action  of  this  acid  can  be  estimated. 
The  utility  of  this  estimation  will  be  pointed  out  as  we 
proceed. 

When  all  the  operations  necessary  for  each  particular 
case  have  been  completed,  we  know  the  proportion  of  vola- 
tile substances,  of  substances  soluble  in  acetic  acid,  and 
those  insoluble  in  hydrochloric  and  sulphuric  acids,  con- 
tained in  the  substance  under  assay. 

Let  A  be  the  weight  of  the  rough  or  non-calcined  ore  ; 
B  the  weight  of  the  same  calcined  ;  C  the  weight  of  the 


THE   ASSAY   OF   IRON   IN   THE   DRY   WAY.  315 

fluxes  in  a  rough  state  ;  D  the  weight  of  the  same  calcined  ; 
P  the  weight  of  matter  insoluble  in  hydrochloric  or  sul- 
phuric acids  ;  E  the  weight  of  the  fixed  substances  soluble 
in  acetic  or  nitric  acids,  —  a  weight  which  can  be  readily 
calculated  when  we  know  the  loss  which  the  ore,  not 
treated  by  acids,  suffers  by  calcination,  and  the  residue  of 
the  treatment  of  this  substance  by  acetic  or  nitric  acid  ;  M 
the  weight  of  the  button  of  metal  and  scattered  globules  ; 
S  the  weight  of  the  slag  ;  and  0  the  loss  of  weight  in  the 
assay,  which  represents  the  quantity  of  oxygen  disengaged 
during  the  reduction. 

The  following  is  the  disposition  of  the  data  from  which, 
at  one  view,  all  the  useful  results  of  the  assay  can  be  deter- 
mined. 

In  the  assay  has  been  employed  :  — 

A,  rough  ore  =  calcined  ore       .         .         .         .         .     B 

B,  of  rough  fluxes  added  =  fixed  flux        .  .    D 

Total  of  fixed  matter    B  +  D 

The  result  has  been  :  — 

-M    {Total    .....        .        . 


D 

S—  D 
T 

S  —  D  —  T 


Loss          ... 

Fluxes       ....... 

Verifiable  matters      ..... 

Substances  insoluble  in  hydrochloric  acid,  &c. 


Substances  soluble  in  hydrochloric  acid,  &c. 
Substances  soluble  in  acetic  acid  .  . 
Substances  insoluble  in  acetic  acid,  and  soluble  'in 

hydrochloric  acid     .        .        .         .         .         .         S—  D—  T—  R 

When  the  iron  in  the  substance  assayed  is  in  a  known 
degree  of  oxidation,  and  when  but  little  manganese  is 
present,  the  quantity  of  oxygen  0  ought  to  correspond 
very  nearly  with  the  quantity  of  metal  M  produced  ;  if  it 
does,  the  assay  must  be  correct. 

A  rigorous  correspondence  between  the  two  numbers, 
however,  cannot  always  be  obtained,  because  the  iron  is 
not  pure,  but  always  contains  carbon,  so  that  in  ordinary 
assays  the  ferric  oxide  loses  but  from  twenty-eight  to 
twenty-nine  per  cent,  of  oxygen. 


316  THE   ASSAY   OF   IRON   IN   THE   DRY   WAY. 

On  the  other  hand,  the  quantity  of  iron  remaining  in 
the  slag  makes  up  in  part  for  the  carbon  combined  with 
the  metal'  reduced ;  but  when  the  assay  has  been  made 
with  a  suitable  flux,  the  quantity  of  oxide  remaining  is 
very  small,  and  never  exceeds  one  per  cent,  of  the  weight 
of  the  slag.  When  the  iron  is  in  an  unknown  degree 
of  oxidation,  the  loss  0  produced  in  the  assay  gives  the 
degree,  if  it  has  been  made  without  accident ;  but  if  there 
is  any  doubt,  and  the  result  is  of  importance,  the  assay 
must  be  recommenced  for  verification.  If  the  ferruginous 
matter  contain  manganese,  and  if  that  metal  be  in  the 
state  of  protoxide,  the  verification  just  described  can  be 
made  without  modification,  because  the  manganese  dis- 
solved in  the  slag  is  always  at  the  minimum  of  oxidation  ; 
and  when  a  sufficient  quantity  of  flux  is  employed,  the 
amount  reduced  is  of  no  consequence.  But  when  the 
manganese  is  in  the  state  of  red  oxide,  it  parts  with  a 
certain  quantity  of  oxygen  on  being  reduced  to  the 
minimum  of  oxidation,  and  which  quantity  is  estimated 
in  the  loss  0,  so  that  a  perfectly  accurate  verification 
cannot  be  made.  Nevertheless,  the  difference  between 
the  loss  0,  and  the  quantity  of  oxygen  calculated  from 
the  metal  M,  cannot  be  very  great,  because  the  red  oxide 
of  manganese  loses  but  -068  of  oxygen  in  its  transforma- 
tion to  protoxide. 

If  the  assay  has  been  made  with  care,  the  loss  of 
oxygen  indicates  the  amount  of  iron  in  a  very  approxi- 
mate manner,  and  nearly  always  with  an  exactitude 
which  is  surprising  to  those  not  accustomed  to  this  kind 
of  operation. 

Titanic  acid  behaves  in  iron  assays  exactly  as  the 
oxides  of  manganese  ;  it  disengages  at  most  but  -06  of 
oxygen  when  dissolved  in  the  earthy  glasses  in  contact 
with  charcoal. 


THE   ASSAY   OF   IRON   IX   THE   WET   WAY. 


B.    THE   ASSAY   OF   IRON   AND    ITS   ORES   IN   THE   WET   WAY. 

This  will  be  subdivided  into  the  following  sections  : — 

a.  Assay  of  iron  ores,  pig-iron,  and  steel,  for  the  metallic 
iron  they  contain. 

/?.  Complete  assay  of  iron  ores. 

y.  Estimation  of  carbon,  sulphur,  phosphorus,  silicon, 
&c.,  or  metallic  iron  and  steel. 

Dr.  Penny's  Process. — The  following  method  of  deter- 
mining the  amount  of  iron  in  a  sample  by  means  of  a 
normal  solution,  has  been  contrived  by  Dr.  F.  Penny,  who 
was  led  to  substitute  potassium  bichromate  for  potassium 
permanganate,  as  recommended  by  Marguerite.  The 
reason  of  employing  the  bichromate  is,  that  it  is  an 
unchangeable  salt,  whilst  the  permanganate  sometimes 
undergoes  decomposition,  so  that  its  strength  is  variable, 
and  each  series  of  experiments  made  with  it  requires  a 
separate  verification  by  means  of  a  weighed  quantity  of 
pure  iron.  This  inconvenience  is  avoided  in  Dr.  Penny's 
method,  which  is  described  in  his  own  words  as  under  :— 

'  In  the  first  series  of  experiments,  pure  harpsichord 
wire  was  dissolved  with  every  care  in  hydrochloric  acid, 
and  potassium  bichromate  added  to  the  solution  until  the 
conversion  of  the  iron  protochloride  into  the  perchloride 
was  complete.  I  obtained  the  following  results  : — 

Iron.  Bichromate. 

1  Exp.  I.  50  grs.  required      44-4  grs. 

„     II.  397  „          „  35-2  „ 

„    'HI.  48-3  „         „  42-8  „ 

„     TV.  65-3  „         „  49-2,, 

'  The  mean  of  these  results  is,  100  parts  of  iron  to 
88-75  of  bichromate. 

'  In  the  second  series  of  experiments  ferrous  sulphate 
was  employed.  This  salt  was  made  from  ferrous  sulphide, 
and  purified  most  carefully  by  repeated  crystallisation. 
A  known  quantity  of  it  was  dissolved  in  water,  acidulated 
with  either  pure  hydrochloric  or  sulphuric  acid,  and  the 
solution  treated  with  bichromate  : — 


318  THE   ASSAY   OF    IRON   IN   THE   WET   WAY. 

Sulphate  of  iron.  Bichromate. 

<  Exp.  I.  100  grs.  required  17-90  grs. 

„     II.  180  „         „  32-10,, 

„      III.  150  „         „  26-82  „ 

„      IV.  120  „         „  21-40  „ 

'  These  experiments  give  the  ratio  of  100  parts  of 
ferrous  sulphate  to  17*867  of  bichromate,  or  100  of  iron 
to  88*71,  which  corresponds  very  closely  to  the  mean 
result  obtained  with  the  metallic  iron.  Moreover,  I  per- 
formed a  series  of  similar  experiments  with  the  neutral 
potassium  chromate,  and  obtained  results  completely 
confirmatory  of  the  general  accuracy  of  the  foregoing 
experiments.  We  may  therefore,  I  think,  safely  conclude 
that  100  parts  of  metallic  iron  correspond  to  88*75  of  the 
potassium  bichromate,  and  that  100  of  the  latter  are  equal 
to  112-67  of  the  former. 

4 1  shall  now  proceed  to  describe  the  method  of  employ- 
ing the  potassium  bichromate  for  the  determination  of  the 
amount  of  iron  in  clay-band  and  black-band  ironstone.  I 
shall  be  purposely  minute,  as  I  particularly  desire  that 
the  process  may  be  serviceable  to  those  who,  from  their 
pursuits  in  life,  are  interested  in  the  value  and  quality  of 
ironstone,  and  who  may  be  imperfectly  acquainted  with 
analytical  operations. 

'  A  convenient  quantity  of  the  specimen  is  reduced  to 
coarse  powder,  and  one-half  at  least  of  this  still  further 
pulverised,  until  it  is  no  longer  gritty  between  the  fingers. 
The  test  solution  of  potassium  bichromate  is  next  prepared. 
44-4  grs.  of  the  salt  in  fine  powder  are  weighed  out,  and 
put  into  an  alkalimeter  (graduated  into  100  equal  divisions), 
and  tepid  distilled  water  afterwards  poured  in  until  the 
instrument  is  filled  to  0.  The  palm  of  the  hand  is  then 
securely  placed  on  the  top,  and  the  contents  agitated  by 
repeatedly  inverting  the  instrument,  until  the  salt  is  dis- 
solved and  the  solution  rendered  of  uniform  density 
throughout.  It  is  obvious  that  each  division  of  the 
solution  thus  prepared  contains  0-444  gr.  of  bichromate, 
which  corresponds  to  ^  a  gr.  of  metallic  iron.  The 
potassium  bichromate  used  for  this  process  must  of  course 


DR.  PENNY'S  PROCESS.  310 


be  purchased  pure,  or  made  so  by  repeated  crystallisation, 
and  it  should  be  thoroughly  dried  by  being  heated  to 
incipient  fusion. 

fc  100  grs.  of  the  pulverised  ironstone  are  now  intro- 
duced into  a  Florence  flask,  with  1^  oz.  by  measure  of 
strong  hydrochloric  acid,  and  \  an  ounce  of  distilled 
water.  Heat  is  cautiously  applied,  and  the  mixture  occa- 
sionally agitated,  until  the  effervescence  caused  by  the 
escape  of  the  carbonic  acid  ceases ;  the  heat  is  then 
increased,  and  the  mixture  made  to  boil,  and  kept  at 
moderate  ebullition  for  ten  minutes  or  a  quarter  of  an 
hour.  During  these  operations  it  will  be  advisable  to 
incline  the  flask,  in.  order  to  avoid  the  projection,  and 
consequent  loss,  of  any  portion  of  the  liquid  by  spirting. 
About  6  oz.  of  water  are  next  added,  and  mixed  with  the 
contents  of  the  flask,  and  the  whole  rapidly  transferred  to 
an  evaporating  basin.  The  flask  is  rinsed  several  times 
with  water,  to  remove  all  adhering  solution. 

'  Several  small  portions  of  a  weak  solution  of  pure  red 
potassium  prussiate  (containing  one  part  of  the  salt  to  40 
of  water)  are  now  dropped  upon  a  white  porcelain  slab, 
which  is  conveniently  placed  for  testing  the  solution  in 
the  basin  during  the  next  operation. 

'  The  prepared  solution  of  potassium  bichromate  in  the 
alkalimeter  is  then  added  very  cautiously  to  the  solution  of 
iron,  which  must  be  repeatedly  stirred,  and  as  soon  as  it 
assumes  a  dark  greenish  shade,  it  should  be  occasionally 
tested  with  the  red  potassium  prussiate.  This  may  be 
easily  done  by  taking  out  a  small  quantity  on  the  top  of  a 
glass  rod,  and  mixing  it  with  a  drop  of  the  solution  on  a 
porcelain  slab.  When  it  is  noticed  that  the  last  drop 
communicates  a  distinct  red  tinge,  the  operation  is  ter- 
minated. The  alkalim-eter  is  allowed  to  drain  for  a  few 
minutes,  and  the  number  of  divisions  in  the  test-liquor 
consumed  read  off.  This  number  multiplied  by  two  gives 
the  amount  of  iron  per  cent,  in  the  specimen  of  ironstone, 
assuming  that,  as  directed,  100  grs.  have  been  used  for 
the  experiment.  The  necessary  calculation  for  ascertain- 
ing the  corresponding  quantity  of  protoxide  is  obvious. 


320  THE   ASSAY   OF    IRON   IN   THE   WET   WAY. 

'When  black-band  ironstone  is  the  subject  of  ana- 
lysis, or  when  the  ore  affords  indications,  by  its  appear- 
ance or  during  the  treatment  with  hydrochloric  acid,  that 
it  contains  an  appreciable  quantity  of  carbonaceous 
matter,  then  the  hydrochloric  acid  solution  must  be 
filtered  before  being  transferred  to  the  basin,  and  the 
filter,  with  the  insoluble  ingredients,  must  be  washed  in 
the  usual  way  with  warm  distilled  water,  slightly  acidu- 
lated with  hydrochloric  acid  until  the  filtrate  ceases  to 
give  a  blue  colour  with  the  red  potassium  prussiate. 
In  those  cases,  also,  where  the  presence  of  iron  pyrites  in 
the  ironstone  is  suspected,  it  will  be  necessary  to  remove 
the  insoluble  matter  by  filtering  before  applying  the 
bichromate  solution  ;  but  with  ironstones  in  which  the 
insoluble  ingredients  are  merely  clay  and  silica,  filtration 
is  not  essential. 

4  Now  it  is  evident  that  the  foregoing  process,  so  far  as 
I  have  described  it,  serves  for  the  determination  of  that 
portion  of  iron  only  which  exists  in  the  ore  in  the  state 
of  protoxide.  But  many  specimens  of  the  common  iron- 
stone of  this  country  contain  appreciable  quantities  of 
ferric  oxide,  which,  being  unacted  upon  by  the  potas- 
sium bichromate,  would  escape  estimation  by  the  present 
method.  By  an  additional  and  easy  operation,  however, 
the  amount  of  metallic  iron  in  the  ingredient  may  be 
likewise  determined.  It  is  only  necessary  to  reduce  it 
to  the  minimum  state  of  oxidation  and  then  to  add  the 
bichromate  as  previously  directed. 

'  The  best  and  most  convenient  agent  for  effecting  the 
reduction  of  the  ferric  oxide  is  sodium  sulphite.  The 
only  precaution  to  be  observed  is  to  use  it  in  sufficient 
quantity,  and  at  the  same  time  to  take  care  that  the  iron 
Golution  contains  excess  of  acid.  When  the  reduction  is 
complete,  a  few  minutes'  ebullition  suffices  to  decompose 
the  excess  of  sodium  sulphite,  and  effectually  to  expel 
every  trace  of  sulphurous  acid. 

'  In  order  to  test  the  exactness  of  this  mode  of 
estimating  the  iron  of  the  peroxide,  I  made  several  ex- 
periments with  peroxide  prepared  from  known  quantities 


DR.  PENNY'S  PROCESS.  321 

of  pure  iron  wire.  The  peroxide  was  thoroughly  washed, 
dissolved  in  hydrochloric  acid,  reduced  with  sulphite 
of  soda,  and  after  complete  expulsion  of  the  excess  of 
sulphurous  acid,  the  solution  was  diluted  with  water  and 
treated  with  potassium  bichromate.  I  select  three  of  the 
experiments  : — 

1  Exp.  I.        10  grs.  of  iron  consumed       8*87  of  bichromate 
„      II.      18    „          „          „  15-94 

„     UI.     25    „          „          „  22-15 

'  The  mean  of  all  my  experiments  on  this  point  gives 
the  ratio  of  100  of  iron  to  88*6  of  bichromate,  which  is  in 
close  accordance  with  the  former  results. 

'  Whenever,  therefore,  the  ore  of  iron  contains  ferric 
oxide  it  will  be  necessary  to  add  sodium  sulphite  to 
the  hydrochloric  acid  solution  before  the  addition  of  the 
test-liquor  from  the  alkalimeter.  The  sulphite  should 
be  dissolved  in  distilled  water,  and  added  to  the  solution 
of  iron  in  small  successive  portions,  until  a  drop  of  the 
liquor  gives  merely  a  rose-pink  colour  with  potassium 
sulphocyanide,  which  indicates  that  the  reduction  of  the 
ferric  salt  is  sufficiently  perfect.  The  liquor  is  now 
heated  till  the  odour  of  sulphurous  acid  is  no  longer 
perceptible.  These  operations  should  be  performed  while 
the  solution  is  in  the  flask,  and  before  it  is  filtered  or 
transmitted  to  the  basin. 

'  I  will  here  mention  for  the  guidance  of  those  who 
may  not  be  fully  aware  of  the  reactions  of  the  oxides  oi 
iron,  that  the  existence  of  an  appreciable  quantity  of 
peroxide  in  the  ironstone  may  be  readily  discovered  by 
dissolving  (as  directed  in  the  process)  39  or  40  grs  of  the 
ore  in  hydrochloric  acid,  diluting  with  about  8  oz.  of 
water,  filtering,  and  testing  a  portion  of  the  solution  with 
potassium  sulphocyanide.  If  a  decided  dark  blood-red 
colour  is  produced,  the  quantity  of  ferric  oxide  in  the 
stone  must  be  determined  ;  but  if  the  eolour  is  only  light 
red  or  rose-pink,  the  proportion  is  exceedingly  small,  and 
for  practical  purposes  not  worth  estimating.  Of  course, 
when  the  specimen  of  ironstone  has  an  ochrey  or  a  reddish 

Y 


322  THE   ASSAY   OF   IRON    IN   THE   WET   WAY. 

appearance  on  the  surface  or  in  the  fracture  the  presence 
of  a  large  proportion  of  ferric  oxide  is  indicated,  and  its 
exact  quantity  must  be  determined. 

4  In  conclusion,  I  must  not  omit  to  notice  one  or  two 
circumstances  which  appear  at  first  to  militate  against  th£ 
accuracy  of  this  process.  It  may  be  questioned  whether 
solutions  of  the  ferrous  salts  do  not  absorb  oxygen  so 
rapidly  from  the  air  as  to  influence  the  results  obtained 
by  this  method.  Marguerite  has  shown,  and  my  own 
observations  completely  confirm  his  statement,  that  ferrous 
salts  in  an  acid  solution  become  peroxidised  very  slowly  ; 
and,  in  a  particular  experiment,  I  found  that  contact  with 
the  air  during  several  hours  caused  no  diminution  in  the 
quantity  of  potassium  bichromate  required.  As  the  pro- 
cess may  be  completed  in  a  few  minutes,  it  is  certain  that 
no  inaccuracy  can  arise  from  this  cause. 

'  It  is  also  important  to  inquire  whether  the  chromic 
acid  in  the  potassium  chromate  may  not  be  partially 
deoxidised  by  hydrochloric  acid  alone  without  the  presence 
of  a  ferrous  salt.  Such  a  reaction  would  obviously  give 
rise  to  a  serious  error.  It  is  well  known  that  concentrated 
hydrochloric  acid  rapidly  decomposes  the  chromic  acid 
of  the  chromates  when  aided  by  the  application  of  heat. 
But  I  have  satisfied  myself,  by  numerous  experiments, 
that  this  acid  exerts  very  little  appreciable  action  upon 
dilute  solutions  of  the  potassium  chromates,  either  cold 
or  warm,  and  that  the  action  is  only  partial  even  after 
continued  ebullition ;  so  that  the  present  method  is  free 
from  inaccuracy  on  this  account.' 

4.  Titration  of  Iron  by  Tin  Protochloride. — Mr.  Button, 
in  his  excellent  '  Volumetric  Analysis  '  before  quoted,  gives 
the  following  directions  for  the  direct  titration  of  iron  by 
tin  protochloride. 

The  principle  involved  in  this  reaction  is,  in  fact,  simply 
a  reversion  of  the  ordinary  process  by  permanganate  and 
bichromate.  In  the  case  of  these  two  reagents,  the  amount 
of  oxygen  given  up  by  them  is  the  measure  of  the  quantity 
of  iron,  whereas  with  tin  protochloride  it  is  the  amount 
taken  up  by  it  that  answers  the  same  purpose. 


PROTOCHLORIDE   OF   TIX   PROCESS.  323 

Fresenius  (in  his  '  Zeitschrift  fur  analytische  Chemie,' 
part  1,  page  26)  has  recorded  a  series  of  experiments 
made  on  the  weak  points  of  this  process,  and  gives  it 
as  his  opinion  that  it  is  most  accurate  and  reliable,  with 
proper  care.  The  summary  of  his  paper  is  as  follows  : — 

a.  A  solution  of  ferric  oxide  of  known  strength  is  first 
prepared,  by  dissolving  10-03  grm.  fine  pianoforte  wire 
(  =  10  grm.  pure  iron)  in  pure  hydrochloric  acid,  adding 
chlorate  of  potash  to  complete  oxidation  ;  boiling  till  the 
excess  of  chlorine  is  removed,  and  diluting  the  solution  to 
1  litre. 

b.  A   clear   solution   of  tin    protochloride,    of   such 
strength  that  about  equal  volumes  of  it  and  the  iron  solu- 
tion are  required  for  the  complete  reaction. 

c.  A  solution  of  iodine  in  potassium  iodide,  containing 
about  0-005  grm.  iodine  in  1  c.c.  (If  the  operator  has  the 
ordinary  decinormal  iodine  solution  at  hand,  it  is  equally 
applicable.)     The  operations  are  as  follows  :— 

1.  1  or  2  c.c.  of  the  tin  solution  are  put  into  a  beaker 
with  a  little  starch  liquor,  and  the  iodine  solution  added 
from  a  burette  till  the  blue  colour  occurs ;  the  quantity  is 
recorded. 

2.  10  c.c.  of  the  iron  solution  =  0-1  grm.  iron  are  put 
into  a  small  flask  with   a   little  hydrochloric  acid,   and 
heated  to  gentle  boiling  (preferably  on  a  hot  plate) ;  the 
tin  solution  is  then  allowed  to  flow  in  from  a  burette  until 
the  yellow  colour  of  the  solution  is  nearly  destroyed  ;   it  is 
then  added  drop  by  drop,  waiting  after  each  addition  until 
the  colour  is  completely  gone  and  the  reduction  ended. 
If  this  is  carefully  managed  there  need  be  no  more  tin  solu- 
tion added  than  is  actually  required  ;  however,  to  guard 
against  any  error  in  this  respect,  the  solution  is  cooled,  a 
little  starch  liquor  added,  and   the  iodine  solution  added 
by  drops  until  a  permanent  blue  colour  is  obtained.     As 
the  strength  of  the  iodine  solution  compared  with  the  tin 
has  been  found  in  1,  the  excess  of  tin  solution  correspond- 
ing to  the  quantity  used  is  deducted  from  the  original 
quantity,  so  that  by  this  means  the  volume  of  tin  solution 
corresponding  to  O'l  grm.  iron  is  found. 

Y  2 


324  THE   ASSAY   OF   IRON   IN   THE   WET   WAY. 

The  operator  is,  therefore,  now  in  a  position  to  estimate 
any  unknown  quantity  of  iron  which  may  exist  in  a  given 
solution,  in  the  ferric  state,  by  means  of  the  solution  of 
tin. 

If  the  iron  should  exist  partly  or  wholly  in  the  ferrous 
state,  it  must  be  oxidised  by  the  addition  of  potassium 
chlorate,  and  boiled  to  dissipate  the  excess  of  chlorine,  as 
described  in  2. 

Example:  10  c.c.  of  iron  solution,  containing  O'l  grm. 
iron,  required  15  c.c.  of  tin  solution. 

A  solution,  containing  an  unknown  quantity  of  iron, 
was  then  taken  for  analysis,  which  required  12  c.c.,  con- 
sequently, a  rule  of  three  sum  gave  the  proportion  of  iron 
as  follows  : — 

15  :  01  grm.  ::12  :  0'08  grm. 

It  must  be  remembered  that  the  solution  of  tin  is 
not  permanent,  consequently  it  must  be  tested  every  day 
afresh.  Two  conditions  are  necessary  in  order  to  ensure 
accurate  results. 

1st.  The  iron  solution  must  be  tolerably  concentrated, 
since  the  end  of  the  reduction  by  loss  of  colour  is  more 
distinct ;  and,  further,  the  dilution  of  the  liquid  to  any 
extent  interferes  with  the  quantity  of  tin  solution  neces- 
sary to  effect  the  reduction.  Fresenius  found  that  by 
diluting  the  10  c.c.  of  iron  solution  with  30  c.c.  of  distilled 
water,  y^  of  a  c.c.  more  was  required  than  in  the  concen- 
trated state.  This  is,  however,  always  the  case  with  tin 
protochloride  in  an  acid  solution,  and  constitutes  the  weak 
point  in  Streng's  method  of  analysis  by  its  means :  it 
would  seem  that  dilution  either  predisposed  it  to  rapid  oxi- 
dation, or  that  water  had  the  power  within  itself  to  com- 
municate a  certain  proportion  of  oxygen  to  it. 

2nd.  The  addition  of  the  tin  solution  to  the  iron  must 
be  so  regulated  that  only  a  very  small  quantity  of  iodine 
is  necessary  to  estimate  the  excess — if  this  is  not  done 
another  source  of  error  steps  in,  namely,  the  influence  which 
dilution,  on  the  one  hand,  or  the  presence  of  great  or  small 


PROTOCHLORIDE   OF   TIX   PKOCESS.  32S 

quantities  of  hydrochloric  acid  on  the  other,  is  known  to 
exercise  over  this  reaction.  Practically  it  was  found  that 
where  the  addition  of  tin  to  the  somewhat  concentrated 
iron  solution  was  cautiously  made,  so  that  the  colour  was 
just  discharged,  the  mixture  then  rapidly  cooled,  starch 
added,  and  iodine  till  blue,  the  estimation  was  as  reliable 
as  by  any  other  method. 

Messrs.  Stock  and  Jack  ('Chemical  News,'  Feb.   12, 
1875),  modify  this  process  as  follows : — 

1  grm.  of  ore  is  dissolved  in  30  c.c.  of  strong  HC1,  or 
if  not  decomposed  by  HC1  it  is  first  fused  with  alkaline 
carbonate,  and  brought  into  HC1  solution ;  in  either  case, 
the  solution  is  made  up  to  500  c.c.  with  distilled  water, 
and  caused  to  boil.  The  stannous  chloride  may  now  be 
added  in  small  portions  at  a  time,  but  it  must  be  in  dilute 
clear  acid  solution,  a  convenient  strength  containing  10 
grms.  of  tin  per  litre.  The  colour  of  the  ferric  solution  is 
a  fair  guide  to  the  addition  of  the  tin-salt  within  certain 
limits  ;  but  when  the  colour  becomes  faint  some  other 
indicator  must  be  used,  and  this  we  find  in  a  dilute,  recently 
prepared  solution  of  potassium  sulphocyanide,  which  is 
disposed  in  drops  over  the  surface  of  a  white  tile.  Special 
care  must  be  taken  to  add  the  trial  drops  of  iron  solution 
quickly  to  those  on  the  tile,  and  to  have  the  beaker  con- 
taining the  solution  in  pretty  close  proximity  to  the  tile, 
so  as  to  guard  against  oxidation  of  solution  on  the  glass 
rod  with  which  the  test  drops  are  added.  The  reduction 
is  carried  so  far  that  only  a  faint  tinge  of  pink  is  produced, 
when  the  last  addition  of  tin-salt  has  been  made  and 
allowed  to  boil  for  a  few  moments.  The  next  step  is  the 
titration  with  potassium  bichromate ;  and,  as  a  vital  part 
of  the  process,  we  make  the  preliminary  addition  of  three 
drops  of  bichromate  (standard  solution  1  c.c.  =  0*01  grm. 
iron),  then  test  with  potassium  sulphocyanide.  A  distinct 
access  of  colour  in  this  test,  as  compared  with  the  last  test 
made  in  reducing,  is  accepted  as  proof  of  the  absence  of 
stannous  salt,  and  it  only  remains  to  complete  the  assay  in 
the  usual  manner. 

The  tin  solution  is  best  prepared  by  placing  fragments 


326  COMPLETE   ASSAY   OF   IRON   ORES. 

of  pure  tin  at  the  bottom  of  a  beaker,  laying  a  small  plati- 
num crucible  or  cover  upon  them,  and  covering  the  whole 
with  equal  parts  of  pure  hydrochloric  acid  and  water :  a 
large  watch-glass  or  porcelain  capsule  should  be  placed  on 
the  top  of  the  beaker,  to  exclude  air  and  prevent  loss  by 
spirting. 

The  contact  of  the  platinum  with  the  tin  sets  up  a  gal- 
vanic current,  which  materially  hastens  the  solution  of  the 
tin  without  at  all  affecting  the  platinum  ;  when  the  acid  is 
all  saturated,  it  may  be  poured  off  and  fresh  added  until 
sufficient  solution  has  been  obtained.  The  whole,  freely 
acidified  and  diluted  to  a  convenient  strength,  should  be 
placed  in  a  well-stoppered  bottle,  with  a  few  fragments  of 
tin  ;  its  strength,  which  is  constantly  lessening  to  a  slight 
extent,  must  be  found  before  using  it. 

ft.  Complete  Assay  of  Iron  Ores. — The  ordinary  con- 
stituents of  clay  ironstone  (which  is  about  the  most  com- 
plex, and  of  which  the  details  of  the  analysis  will  be  the 
most  useful)  are  the  ferric  and  ferrous  oxides,  manganese 
oxide,  alumina,  magnesia,  lime,  potash,  soda,  sulphur, 
phosphoric  acid,  carbonic  acid,  silica,  and  water. 

Some  iron  ores  dissolve  very  readily  in  hydrochloric 
acid  or  in  aqua  regia  ;  others  do  not,  even  when  they  are 
in  a  very  fine  state  of  division  ;  but  all  do  readily  after 
fusion  with  an  alkali,  or  an  alkaline  carbonate — as  of  potash 
or  soda ;  hence  it  is  advisable  to  fuse  the  finely-pulverised 
ore  with  an  alkali  previous  to  attempting  its  solution  in  an 
acid. 

Determination  of  Silica,  Iron  Oxide,  and  Manganese 
Oxide. — The  ore  must  be  reduced  to  the  finest  possible 
state  of  division,  a  small  quantity  placed  in  a  test-tube,  and 
boiled  for  some  time  with  hydrochloric  acid.  If  it  com- 
pletely decomposes  it  need  not  be  submitted  to  fusion  with 
sodium  carbonate,  but  100  grs.  may  be  at  once  weighed 
off,  and  treated  in  a  Florence  flask  with  about  2  ounces 
of  hydrochloric  acid,  gradually  heated  to  ebullition,  and 
that  temperature  maintained  until  perfect  decomposition 
has  ensued.  If,  on  the  other  hand,  the  ore  does  not  com- 
pletely decompose,  100  grs.  must  be  carefully  mixed  with 


COMPLETE   ASSAY   OF   IRON   ORES. 


327 


500  or  600  grs.  of  sodium  carbonate  placed  in  a  platinum 
crucible  and  fused  at  a  bright  red  heat ;  the  fusion  must 
continue  about  half  an  hour.  It  may  be  here  mentioned 
that  the  platinum  crucible,  previous  to  its  introduction 
into  the  furnace,  must  be  placed  in  one  of  clay  furnished 
with  a  cover  and  embedded  in  magnesia,  to  protect  it  from 
the  injurious  effect  of  contact  with  the  crucible  or  fuel. 

When  the  platinum  crucible  and  its  contents  are  cold, 
it  is  placed  in  a  large  evaporating  basin,  and  pure  dilute 
hydrochloric  acid  poured  over  it :  the  fused  mass  dissolves 
with  effervescence,  and  more  acid  must  be  gradually  added 
as  seems  necessary,  until  no  further  action  takes  place. 
The  solution  being  finished,  the  crucible  is  removed,  washed 
with  distilled  water,  and  the  whole,  together  with  the 
washings,  evaporated  to  dryness.  The  solution  obtained 
in  the  first  case,  in  which  the  ore  was  wholly  decomposable 
by  hydrochloric  acid  alone,  is  also  to  be  evaporated  to  dry- 
ness.  The  object  of  this  evaporation  is  the  conversion  of 
the  silica  the  ore  may  contain,  from  a  partiaRy  soluble  to 
a  completely  insoluble  state,  so  that  the  whole  of  it  may 
be  collected  and  weighed. 

Towards  the  end  of  the  opera- 
tion, the  partially-dried  mass  must 
be  continually  stirred,  in  order 
to  prevent  losses  by  the  spirting 
which  will  otherwise  take  place. 
When  cold,  the  contents  of  the 
basin  are  moistened  with  hydro- 
chloric acid,  and  the  whole  left  to 
itself  for  about  one  hour.  It  is 
then  mixed  with  a  small  quantity 
of  distilled  water,  gently  warmed 
and  thrown  upon  a  filter.  Every 
constituent  of  the  ore,  with  the 
exception  of  the  silica,  will  pass  through  the  filter  in  a 
liquid  state.  The  silica  remaining  in  the  filter  is  to  be 
well  washed  with  hot  water,  dried,*  ignited  in  a  platinum 
crucible,  and  weighed. 

*  The  most  convenient  form  of  apparatus  for  drying  precipitates,  61ters,  &e 
in  analysis,  is  a  little  water-oven,  called  a  '  water-bath '  (see  fig.  90).     It  con 


FIG.  90. 


328  COMPLETE   ASSAY   OF    IRON    ORES, 

To  the  liquid  filtered  from  the  silica,  and  with  which 
the  washings  have  been  incorporated,  add  a  few  drops  of 
nitric  acid,  and  boil ;  when  cool,  add  gradually  pure  preci- 
pitated barium  carbonate  until  in  excess,  which  point  may 
be  ascertained  by  cessation  of  effervescence,  and  by  some 
of  the  carbonate  remaining  undissolved.  The  whole  is  now 
to  be  kept  at  a  gentle  heat  for  about  an  hour,  and  then 
poured  on  a  filter,  in  which  will  remain  the  ferric  oxide, 
alumina,  .and  phosphoric  acid,  together  with  the  excess  of 
barium  carbonate  employed.  The  liquid  which  has  passed 
through  the  filter  is  mixed  with  excess  of  ammonium  sul- 
phide, covered  with  a  glass  plate  to  exclude  air,  and  left 
to  itself  for  four  or  five  hours.  If  any  manganese  were 
present  in  the  ore,  it  will  now  be  thrown  down  as  a  flesh- 
red  precipitate,  which  must  be  collected  on  a  filter,  washed, 
dissolved  in  a  small  quantity  of  hydrochloric  acid,  the 
solution  filtered,  and  excess  of  sodium  carbonate  added  : 
manganese  carbonate  is  precipitated,  collected  on  a  filter, 
washed,  dried,  ignited,  and  weighed  as  red  oxide,  every 
100  parts  of  which  correspond  to  93  parts  of  manganous 
oxide,  in  which  state  it  usually  exists  in  the  ore.  The 
weight  so  obtained  gives  the  percentage.  The  mixed 
precipitate  of  iron  oxide,  alumina,  barium  carbonate,  and 
phosphoric  acid  remaining  on  the  filter,  is  dissolved  in  a 
small  quantity  of  hydrochloric  acid,  and  the  amount  of  iron 
ascertained  by  Dr.  Penny's  process,  as  already  described. 
As  the  iron  is  in  the  state  of  peroxide,  its  reduction  to 
protoxide  must  be  effected  by  sodium  sulphide,  according 
to  the  method  already  given. 

Determination  of  Lime  and  Magnesia,  and  part  of  the 
Phosphoric  Acid. — Dissolve  another  100  grs.  of  ore  with 
the  precautions  already  pointed  out,  only  in  this  case  the 
silica  may  be  rejected,  and  treat  the  solution  by  the  follow- 
ing process,  which  was  contrived  by  Fresenius  : — 

The  solution  is  heated  to  ebullition  in  a  flask,  and  re- 
duced with  sodium  sulphite,  then  precipitated  with  sodium 

sists  of  a  double  box  of  copper  or  tin  plate  about  six  inches  square,  with  water 
between  the  casings,  which  is  kept  in  a  state  of  ebullition  by  means  of  a  gas- 
flame  or  spirit-lamp. 


COMPLETE   ASSAY   OF   1ROX   ORES.  329 

carbonate,  and  boiled  with  excess  of  caustic  soda  until  the 
precipitate  appears  black  and  granular.  It  is  allowed  .to 
subside,  the  clear  liquid  poured  off,  the  precipitate  washed 
by  decantation  with  hot  water,  and  finally  brought  upon  a 
filter  of  close  texture  and  washed  with  hot  water, 

Treatment  of  the  Precipitate. — The  precipitate  is  again 
transferred,  together  with  the  filter,  into  the  flask,  and 
digested  with  hydrochloric  acid.  When  no  more  black  par- 
ticles are  perceptible  it  is  filtered  ;  the  filter  is  left  whole, 
a  little  water  poured  over  it,  and  the  flask  inclined  so  that 
it  remains  hanging  by  the  side  while  the  liquid  runs  off: 
in  this  manner  it  may  be  quickly  and  completely  washed. 
The  filtered  solution  is  reduced  with  sodium  sulphite,  heated 
to  boiling,  mixed  with  a  few  drops  of  chlorine  water,  then 
with  an  excess  of  sodium  acetate ;  and  when  the  liquid  or  pre- 
cipitate has  not  a  reddish  tint,  chlorine  water  is  added  until 
this  is  the  case.  The  whole  is  boiled  until  the  precipitate 
has  separated,  filtered  hot,  and  the  precipitate,  consisting 
of  ferric  phosphate  and  some  basic  ferric  acetate,  washed. 

To  the  solution  just  filtered  from  the  iron  phosphate, 
add  ammonia  and  ammonium  sulphide,  and  filter  while 
hot ;  this  removes  manganese  and  iron,  leaving  lime  and 
magnesia  alone  in  solution.  The  whole  is  filtered  while 
hot,  and  the  precipitate  remaining  on  the  filter  rejected. 
To  the  filtered  solution  is  added  excess  of  solution  of 
ammonium  oxalate  :  this  throws  down  insoluble  calcium 
oxalate,  which  must  be  collected  on  a  filter,  washed,  dried, 
and  ignited  at  a  low  red  heat.  The  residue  is  now  calcium 
carbonate,  every  100  parts  of  which  correspond  to  56 '29 
parts  of  lime. 

To  the  solution  filtered  from  the  calcium  oxalate,  and 
which  contains  the  magnesia,  add  excess  of  sodium  phos- 
phate, agitate  briskly,  and  set  aside  for  twelve  hours  ;  then 
collect  the  crystalline  precipitate  of  magnesium  ammonio- 
phosphate  on  a  filter,  wash  it  with  water  containing  a  little 
ammonia,  dry  and  ignite  it ;  weigh  the  resulting  magne- 
sium pyro- phosphate  :  every  100  parts  correspond  to  36'67 
parts  of  magnesia. 

The  precipitate  containing  the   sodium  perphosphate 


330  COMPLETE   ASSAY    OF    IROX    ORES. 

and  basic  acetate  is  dissolved  in  hydrochloric  acid,  reduced 
with  sodium  sulphite,  boiled  for  some  time  with  excess  of 
caustic  soda,  and  filtered.  The  filtered  solution  which 
contains  the  phosphoric  acid  is  supersaturated  with  hydro- 
chloric acid,  and  placed  aside  for  future  operation. 

Treatment  of  the  alkaline  solution  poured  off  from  the 
first  black  precipitate.  Determination  of  Alumina  and  re- 
mainder of  Phosphoric  Acid. — The  solution  is  acidulated 
with  hydrochloric  acid,  a  little  potassium  chlorate  added, 
and  then  boiled ;  it  is  then  precipitated  with  ammonia 
(avoiding  a  large  excess),  and  barium  chloride  added  as  long 
as  a  precipitate  appears.  After  digesting  for  some  time  it  is 
filtered.  The  precipitate,  which  contains  the  whole  of 
the  alumina  and  phosphoric  acid,  is  collected  on  a  filter, 
washed  with  a  little  water,  and  dissolved  in  as  little  hydro- 
chloric acid  as  possible.  The  solution  is  saturated  with 
precipitated  barium  carbonate,  gently  warming  ;  an  excess 
of  caustic  soda  is  added,  and  the  heat  still  kept  up.  Any 
baryta  contained  in  the  solution  is  removed  by  sodium  car- 
bonate, which  is  added  until  no  further  precipitation  takes 
place.  The  whole  of  the  alumina  is  now  in  solution,  and 
the  whole  of  the  phosphoric  acid  in  the  precipitate. 

The  solution  is  rendered  acid  with  a  little  hydrochloric 
acid,  boiled  with  a  small  quantity  of  potassium  chlorate, 
precipitated  with  excess  of  ammonia,  and  allowed  to  stand 
for  a  few  hours ;  after  which  the  precipitated  alumina  is 
collected  on  a  filter,  washed,  dried,  ignited,  and  weighed  : 
its  amount  represents  the  percentage  of  alumina  in  the 
ore. 

The  precipitate  containing  the  phosphoric  acid  is  dis- 
solved in  hydrochloric  acid,  the  baryta  precipitated  with 
dilute  sulphuric  acid,  which  is  added  until  no  further  pre- 
cipitate ensues  ;  the  liquid  and  precipitate  are  placed  in  a 
warm  situation  until  the  former  is  quite  bright:  it  is  then 
filtered,  and  to  the  filtered  liquid  is  added  the  small 
portion  reserved,  as  before  directed :  excess  of  ammo- 
nia is  added  to  the  mixture,  then  some  ammonium 
chloride,  and  lastly  magnesium  sulphate.  The  phosphoric 
acid  is  precipitated  as  the  magnesium  ammonio-phosphate, 


COMPLETE   ASSAY   OF   IRON    ORES.  331 

which  is  washed,  dried,  and  ignited,  with  the  precautions 
already  pointed  out.  Every  100  parts  correspond  to 
63-33  parts  of  phosphoric  acid. 

Determination  of  Potash  and  Soda. —  If  the  ore  be 
completely  decomposable  by  hydrochloric  acid,  dissolve  at 
once  100  grs.  in  that  liquid  ;  if  not,  fuse  the  same  quantity 
with  four  times  its  weight  of  barium  hydrate  in  a  platinum 
crucible :  treat  with  hydrochloric  acid,  and  separate  the 
silica  precisely  as  already  described.  To  the  filtered  solution 
add  an  excess  of  baryta  water  ;  this  precipitates  everything 
but  the  potash  and  soda  and  part  of  the  lime.  Throw  the 
whole  on  a  filter,  well  wash  the  precipitate,  and  add  the 
washings  to  the  bulk  of  the  filtered  liquid  ;  to  which  add 
excess  of  ammonia  and  ammonium  carbonate  :  by  these 
reagents  the  small  quantity  of  lime  and  the  excess  of 
baryta  in  solution  are  precipitated.  The  solution  must  now 
be  filtered,  evaporated  to  dryness,  and  ignited.  The  dry 
residue  consists  of  potassium  and  sodium  chlorides,  which 
must  be  weighed,  then  dissolved  in  water  to  which  a  little 
hydrochloric  acid  is  added,  then  excess  of  platinum  chlo- 
ride, and  the  whole  evaporated  to  dryness  in  the  water- 
bath  ;  alcohol  is  now  added,  and  the  whole  thrown  on  a 
small  filter.  The  yellow  precipitate  of  potassium  platino- 
chloride  on  the  filter  is  washed  with  alcohol  until  the 
latter  passes  off  colourless.  The  filter  and  its  contents  are 
then  dried  and  weighed.  Every  100  parts  of  potassium 
platino-chloride  correspond  to  30'56  parts  of  potassium 
chloride.  The  quantity  of  potassium  chloride  thus  ob- 
tained is  deducted  from  the  weight  of  the  mixed  sodium 
and  potassium  chlorides  as  obtained  above ;  the  difference 
will  be  the  amount  of  the  sodium  chloride.  Every  100 
parts  of  sodium  chloride  correspond  to  5 3' 2 8  of  soda,  and 
every  100  parts  of  potassium  chloride  to  63*25  of  potash. 

Determination  of  Sulphur. — Dissolve  100  grs.  of  the 
ore  in  either  of  the  manners  already  described,  separating 
the  silica ;  in  this  case,  however,  a  little  nitric  acid  must 
be  added  to  the  hydrochloric  acid  previous  to  its  mixture 
with  the  ore.  To  the  filtered  solution,  made  somewhat 
dilute,  add  excess  of  barium  chloride,  and  allow  to  stand 


332  COMPLETE    ASSAY   OF    IRON    ORES. 

in  a  warm  place  for  a  few  hours.  Collect  the  precipitate 
of  barium  sulphate  on  a  filter,  wash,  dry,  ignite,  and 
weigh.  Every  100  parts  correspond  to  13 '7 9  parts  of 
sulphur. 

Determination  of  Carbonic  Acid. — The  most  convenient 
apparatus  for  the  determination  of  this  gas  is  that  invented 
by  Fresenius  and  Will,  of  which  the  following  is  a  descrip- 
tion. Fig.  91  shows  its  construction.  A  is  a  large  flask  of 
about  two  ounces  capacity,  in  which  the  decomposition 
of  the  carbonate  is  effected  :  B  a  somewhat  smaller  flask, 
containing  strong  sulphuric  acid :  both  are  supplied  with 
doubly  pierced  corks,  for  the  reception  of  the  three  tubes, 
a,  c,  and  d.  The  tube  a  is  confined  to  the  flask  A,  being 
immersed  below  the  level  of  the  fluid  :  in  the  same  manner, 
d  is  only  connected  with  the  flask  B,  and  only  extends  just 

below  the  cork.     Lastly,  the  tube 
FIG.  91.  .      _    . J '     . 

c  enters  the  neck  of  A  on  the  one 

side,  but  does  not  extend  further, 
and,  by  a  double  bend,  is  brought 
into  connection  with  B,  which  it 
enters,  dipping  into  the  sulphuric 
acid.  The  mouth  of  a  is  closed 
with  wax  during  the  experiment, 
so  that  no  orifice  is  left  in  the 
whole  apparatus  but  the  mouth  of 
the  tube  d. 

The  large  assay  balance,  re- 
presented by  fig.  11,  is  admirably 
suited  for  weighing  this  apparatus. 
100  grs.  of  the  ore  are  introduced  into  the  flask  A, 
which  is  then  filled  with  water  to  about  one-third  ;  the 
apparatus  is  closed  by  the  wax  stopper,  and  brought  into 
equilibrium  on  the  balance  by  a  counterpoise.  The  de- 
composition of  the  carbonate  under  examination  is  now 
induced  by  sucking  out  a  small  quantity  of  air  with  the 
mouth  from  the  tube  d.  The  air  is  thus  drawn  not  only 
from  B,  but  also  from  A,  both  flasks  being  connected  by 
the  tube  c ;  bubbles  of  air  are  therefore  seen  passing  from 
A  through  the  sulphuric  acid  ;  and  in  order  to  restore  the 


COMPLETE   ASSAY   OF    IRON    ORES.  833 

equilibrium  of  pressure,  a  small  quantity  of  sulphuric  acid  is 
forced  from  flask  B  into  flask  A,  where  coming  in  contact 
with  the  carbonate  under  examination,  it  decomposes  it ; 
and  the  carbonic  acid  evolved  with  effervescence  in  A  can 
only  escape  by  the  tube  c  into  the  flask  B,  whence  it  must 
pass  through  the  remainder  of  the  sulphuric  acid  and  the 
tube  d  into  the  air.  This  sulphuric  acid  condenses  with  great 
energy  all  the  aqueous  vapour,  and  retains  everything 
that  the  current  of  gas  might  possibly  carry  with  it.  When 
the  operation  of  removing  a  small  quantity  of  air  by  the 
mouth,  and  the  consequent  addition  of  corresponding 
quantities  of  sulphuric  acid  to  the  contents  of  flask  A, 
have  been  repeated  until  no  more  effervescence  ensues,  the 
decomposition  is  complete. 

There  is  still,  however,  a  portion  of  carbonic  acid  re- 
maining in  the  apparatus  which  was  previously  filled  with 
air,  and  some  still  chugs  to  the  solution  in  the  flask  A, 
which  by  this  time  has  become  cold.  Both  must  be  re- 
moved before  the  apparatus  is  re-weighed.  For  this  pur- 
pose, by  suction,  as  in  the  commencement,  at  d,  so  much 
sulphuric  acid  is  caused  to  pass  over  at  once  as  will  give 
rise  to  a  considerable  elevation  of  temperature  in  A,  by 
which  means  the  carbonic  acid  in  solution  is  evolved,  and 
with  it  that  portion  still  clinging  to  the  other  parts  of  the 
apparatus.  By  removing  the  wax  stopper  &,  the  mouth  of 
a  is  opened,  and  air  may  then  be  drawn  through  the  ap- 
paratus from  d  until  all  the  carbonic  acid  is  expelled. 
Here,  too,  all  the  moisture  which  is  removed  by  the  cur- 
rent of  air  from  A  will  remain  in  the  sulphuric  acid  in  B. 
When  the  whole  apparatus  has  cooled  it  is  placed  upon 
the  scale,  and  the  amount  of  carbonic  acid  is  ascertained 
by  the  weights  which  must  be  added  to  re-establish  the 
equilibrium. 

Determination  of  Water. — Weigh  100  grs.  of  the  ore 
and  ignite  for  a  quarter  of  an  hour  in  a  lightly-covered 
platinum  crucible.  When  cold,  weigh  the  ignited  ore  ; 
the  loss  is  carbonic  acid  and  water.  Deduct  the  amount 
of  carbonic  acid  previously  obtained  from  the  total  loss , 
and  the  remainder  represents  the  quantity  of  water. 


334  ASSAY   OF    IRON. 

Reduction  of  Ferric  to  Ferrous  Salts. — Sulphurous  acid 
or  metallic  zinc  is  the  reducing  agent  usually  employed, 
but  a  much  more  effectual  and  rapid  agent  has  been  pro- 
posed in  sulphuretted  hydrogen  by  Mr.  Eeynolds.  This 
answers  much  better  than  either  zinc  or  sulphurous  acid. 
The  reduction,  even  in  a  strongly  acid  solution,  takes  place 
immediately  ;  and  on  boiling  until  the  sulphuretted  hydro- 
gen is  expelled,  the  sulphur  separated  coagulates  com- 
pletely ;  so  that,  after  allowing  the  solution  to  cool  in  the 
flask  in  which  it  has  been  boiled,  a  cork  being  placed  in 
the  neck  during  the  cooling,  filtration  may  be  effected  so 
rapidly  that  no  oxidation  need  be  feared,  and  the  deter- 
mination may  then  be  effected  with  bichromate,  as  usual. 
It  is  better  to  add  a  considerable  quantity  of  water  to  the 
solution  before  reduction  to  avoid  the  oxidation  which 
would  afterwards  ensue  in  the  filtration  of  a  concentrated 
solution  of  protoxide  of  iron. 

Estimation  of  Ferrous  Oxide  in  the  Presence  of  Ferric 
Oxide. — Messrs.  Wilbur  and  Whittlesey  have  carried  out 
a  suggestion  of  Avery,*  and  applied  it  very  successfully  to 
the  estimation  of  ferrous  and  ferric  oxides  in  silicates  and 
other  ores  of  iron.  Avery  found  that  silica  and  many  sili- 
cates can  be  readily  and  completely  dissolved  by  a  mixture 
of  some  normal  fluoride  with  almost  any  of  the  stronger 
acids,  whether  concentrated  or  dilute. 

These  chemists  have  applied  this  observation  to  the 
estimation  of  the  two  oxides  of  iron,  and  have  obtained  such 
satisfactory  results  that  their  process  deserves  to  be  gene- 
rally adopted  for  the  estimation  of  iron  in  silicates.  The 
method  is  as  follows  : — A  quantity  of  the  finely-powdered 
mineral  to  be  examined  is  weighed  in  a  platinum  crucible  ; 
as  much,  or  rather  more  than  as  much,  powdered  fluor- 
spar (or  of  powdered  cryolite),  free  from  iron,  is  poured 
into  the  crucible  ;  the  powders  are  thoroughly  mixed  by 
stirring  with  a  glass  rod ;  the  rod  is  wiped  clean  upon  a 
fresh  portion  of  the  powdered  fluoride  ;  and  the  latter  is 
thrown  upon  the  mixture  in  the  crucible.  Strong  hydro- 
chloric acid  is  then  poured  into  the  crucible,  until  the 

*   Chemical  News,  vol.  xix.  p.  270. 


ESTIMATION   OF   FERROUS   OXIDE.  335 

powder  is  thoroughly  drenched  and  the  crucible  about 
two-thirds  filled  with  the  liquid.  The  crucible  is  set  upon 
a  water-bath,  and  heated  until  the  iron  has  all  dissolved  : 
the  proportion  of  iron  is  finally  determined  by  titrating 
with  a  standard  solution  of  potassium  permanganate.  To 
protect  the  mineral  from  the  air  during  the  process  of 
solution,  the  crucible  must  be  kept  full  of  some  non- 
oxidising  gas,  which  can  be  either  carbonic  acid  or  coal- 
gas,  as  may  happen  to  suit  the  convenience  of  the 
operator. 

If  carbonic  acid  be  used,  it  is  sufficient  to  cover  the 
crucible  with  a  bit  of  sheet  lead,  perforated  with  two  holes, 
through  one  of  which  is  thrust  a  glass  tube  communicating 
with  a  gas-bottle  in  which  the  carbonic  acid  is  generated, 
while  the  other  serves  as  an  outlet  for  the  escape  of  car- 
bonic acid  and  acid  vapours.  The  crucible  is,  in  this 
case,  simply  set  upon  an  ordinary  water-bath. 

When  coal-gas  is  used  (and  this  agent  is  to  be  preferred 
on  the  whole),  the  apparatus  may  be  arranged  as  follows  : — 
Set  the  charged*  platinum  crucible  upon  a  glass  or  leaden 
tripod,  inside  a  wide  beaker,  in  the  bottom  of  which  there 
is  about  an  inch  of  water.  Invert  a  narrower  beaker 
within  the  first,  so  that  its  mouth  shall  be  sealed  by 
the  water,  and  the  crucible  be  enclosed  in  a  transparent 
chamber.  Coal-gas  is  led  into  this  chamber  through  a 
bent  glass  tube,  which  passes  down  between  the  side  of 
the  upright  and  that  of  the  inverted  beaker,  and  delivers 
the  gas  near  the  top  of  the  chamber.  The  surplus  gas 
escapes  through  another  tube  similarly  bent,  which  starts 
from  a  point  below  the  crucible,  and  is  burned  in  the 
outer  air.  To  facilitate  the  passage  of  the  glass  tubes, 
the  mouth  of  the  inverted  beaker  may  be  made  to  rest 
upon  three  or  four  bits  of  stone  or  metal,  or  an  orifice 
large  enough  to  admit  the  tubes  may  be  made  upon  the 
beaker.  During  the  process  of  solution,  the  upright 
beaker  is  kept  immersed  in  water,  at  or  near  the  tem- 
perature of  boiling.  In  case  the  coal-gas  should  contain 
any  sulphuretted  hydrogen,  it  would  be  well  to  purify  it 
by  means  of  a  potash-tube.  An  hour  and  a  half  is  ample 


336  ASSAY   OF    IRON. 

for  the  solution  of  the  iron  in  O5 — 1  grm.  of  finely- 
powdered  trap-rock.  Fifteen  minutes,  on  the  other  hand, 
will  suffice  for  the  solution  of  0'2  grm.  of  iron  wire.  In- 
stead of  hydrochloric  acid,  sulphuric  acid  may  be  used  to 
act  upon  the  mixture  of  fluor  spar  and  mineral.  The 
calcium  sulphate  frequently  formed  is  objectionable,  from 
its  liability  to  envelope  portions  of  the  mineral,  and  to 
protect  the  iron  from  being  dissolved,  rather  than  from  any 
tendency  to  interfere  with  the  actual  titration. 

Experiments  have  shown  that  the  presence  of  ferric 
oxide  does  not  interfere  in  any  way  with  the  estimation 
of  the  ferrous  oxide.  It  is  found,  also,  by  acting  upon 
weighed  quantities  of  iron  wire  mixed  with  cryolite  and 
iron-alum,  that  the  iron  can  be  estimated  as  well  in  the 
presence  of  the  alum  as  in  its  absence,  provided  only  that 
the  metallic  iron  be  dissolved  in  hydrochloric  acid,  with 
the  necessary  precautions  to  prevent  oxidation,  before 
adding  the  other  ingredients  of  the  mixture.  If  the  iron 
wire,  cryolite,  and  ferric  alum  were  treated  all  at  once 
with  acid,  some  of  the  hydrogen  generated  by  the  solution 
of  the  metallic  iron  would  reduce  a  part  of  the  ferric  salt ; 
so  that  in  the  final .  titration  more  iron  would  be  found 
than  was  introduced  into  the  mixture  in  the  form  of  wire. 

If  time  enough  be  allowed,  finely-powdered  sesqui- 
oxide  of  iron  can  be  dissolved  in  this  way,  even  after 
intense  ignition. 

To  estimate  ferric  oxide  in  a  silicate,  a  separate  por- 
tion of  the  mineral  may  be  treated  with  fluor-spar  and 
acid,  the  solution  reduced  by  zinc  in  a  small  flask  in  the 
usual  way,  arid  the  total  amount  of  iron  determined  with 
bichromate.  Or,  if  the  mineral  contains  only  a  small  pro- 
portion of  ferric  oxide,  it  will  be  sufficient  to  put  a  bit  of 
zinc  into  the  crucible  with  the  mixture  of  mineral,  fluor- 
spar, and  acid.  The  difference  between  the  total  iron  and 
that  determined  as  ferrous  oxide  is  calculated  as  ferric 
oxide. 

Mr.  Allen  effects  solution  of  difficultly  soluble  ores  by 
heating  with  hydrochloric  acid  under  pressure.  This  method 
has  been  used  very  successfully  in  the  analysis  of  various 


ESTIMATION    OF   CARBON.  337 

titanic  iron  ores  and  sands.  About  a  gramme  of  the  finely- 
powdered  mineral  is  heated  in  a  sealed  piece  of  combus- 
tion tubing,  half  full  of  fuming  hydrochloric  acid.  At 
first  the  heat  of  a  water-bath  is  sufficient,  but  after  a  few 
hours  the  temperature  is  gradually  raised  to  140°  or  ]  50°  C. 
The  ore  is  completely  decomposed  in  four  or  five  hours, 
and  after  the  tube  has  cooled  the  end  may  be  broken 
under  water,  and  the  ferrous  oxide  at  once  estimated  by 
bichromate.  The  same  method  will  yield  a  solution  suitable 
for  the  determination  of  the  other  constituents  of  the  ore. 

y.  Estimation  of  Carbon,  Sulphur,  Silicon,  Phosphorus, 
<|*c.,  in  Metallic  Iron  and  Steel. 

Carbon. — This  is  a  problem  of  considerable  difficulty, 
and  to  secure  accurate  results  many  special  precautions  are 
necessary,  owing  to  the  large  preponderance  of  the  iron 
over  the  carbon  present.  The  carbon  may  be  present  in 
two  forms — as  combined  carbon,  and  as  free  or  graphitic 
carbon.  The  estimation  may  be  of  the  total  carbon 
present,  or  of  either  the  combined  or  graphitic  separately, 
and  the  method  of  analysis  adopted  will  have  to  be  selected 
accordingly.  The  following  is  a  description  of  the  most 
satisfactory  processes  which  have  been  devised  for  these 
estimations. 

A.  Estimation  of  the  Total  Carbon.  —  Fresenius 
recommends  that  a  weighed  portion  of  the  metal,  in 
borings  or  chippings,  be  dissolved  in  dilute  sulphuric 
acid  by  the  aid  of  heat.  The  gases  evolved  during 
solution  are  passed  over  red-hot  copper  oxide.  The 
gaseous  hydrocarbons  are  burned,  and  the  carbonic  acid 
formed,  after  drying  by  calcium  chloride,  is  absorbed  by 
potash  solution  in  a  Liebig's  apparatus,  and  thus  weighed. 
This  only  gives  the  combined  carbon,  and  when  an  esti- 
mation of  the  total  carbon  is  required,  the  matter  remain- 
ing behind,  insoluble  in  the  dilute  sulphuric  acid,  is 
collected  and  burned  in  a  stream  of  oxygen,  and  from 
the  weight  of  the  resulting  carbonic  acid  the  amount 
of  carbon  may  be  deduced.  This  quantity,  added  to 
that  obtained  by  burning  the  gases  over  copper  oxide, 

z 


338  ASSAY   OF    IRON. 

gives  the  total  quantity  of  carbon  contained  in  the  iron. 
In  drying  the  insoluble  residue  previous  to  combustion 
in  oxygen,  an  elevated  temperature  must  be  carefully 
avoided  ;  in  fact,  the  safest  way  is  to  dry  over  sulphuric 
acid.  The  presence  of  hydrocarbons  in  the  graphitic 
residue  shows  that  this  process  cannot  be  safely  applied 
for  the  estimation  of  combined  carbon  directly. 

Weyl's  very  ingenious  method  for  the  estimation  of  the 
total  carbon  is  founded  upon  the  fact  that  a  piece  of  iron, 
attached  to  the  positive  pole  of  a  galvanic  battery,  and  sus- 
pended in  hydrochloric  acid,  is  dissolved,  while  the  hy- 
drogen is  given  off  at  the  negative  pole.  The  formation  of 
hydrocarbons,  and  a  consequent  loss,  is  in  this  manner  pre- 
vented. One  great  advantage  in  this  method  is  that  the 
iron  does  not  require  to  be  in  powder.  A  piece  of  iron  2 
to  4  grammes  in  weight,  attached  to  the  positive  pole  of  a 
Bunsen's  cell,  is  suspended  in  dilute  hydrochloric  acid,  just 
below  the  surface  of  the  liquid.  From  the  negative  pole 
hydrogen  passes  off,  while  the  iron  dissolves  quite  quietly, 
and  the  strong  solution  of  ferrous  chloride  formed  may  be 
seen  falling  in  a  regular  stream  through  the  lighter  liquid. 
The  iron  is  dissolved  in  about  twenty-four  hours,  and  the 
carbon  is  left  behind  in  the  same  shape  as  the  piece  of 
metal  from  which  it  was  derived.  In  Weyl's  earlier  ex- 
periments it  was  found  that  some  of  the  liberated  carbon 
at  the  positive  pole  was  carried  over  to  the  negative  pole 
by  the  mechanical  working  of  the  stream.  To  prevent 
this,  a  diaphragm  of  bladder  or  parchment  paper  is  inter- 
posed between  the  two,  wjjich  entirely  obviates  the  possi- 
bility of  loss  in  this  way. 

B.  Estimation  of  th$  Graphite. — Dr.  Eggertz  reduces 
one  gramme  of  iron  to  small  pieces,  mixes  with  5  grammes 
of  pure  iodine  and  5  c.c.  of  water  in  a  small  flask,  covered 
with  a  watch-glass,  and  placed  in  ice-cold  water  before 
adding  the  iron.  It  is  to  be  kept  for  twenty-four  hours  at 
0°  C.,  and  frequently  stirred  meanwhile.  By  keeping  the 
liquid  cold,  no  carburetted  hydrogen  is  produced  The 
greater  the  amount  of  silicon  in  the  iron  the  greater  is  the 
tendency  to  the  production  of  carburetted  hydrogen.  The 


ESTIMATION   OF    GRAPHITE.  339 

residue  of  carbon  and  silica  left  after  the  iron  is  dissolved 
is  collected  on  a  filter  of  known  weight,  when  it  is  dried  at 
from  95°  to  100°  C.,  and  washed  thoroughly  with  hot 
water.  After  twelve  hours,  it  is  to  be  washed  with  a 
mixture  of  hydrochloric  acid  and  twice  its  volume  of 
water,  heated  to  70°  or  80°  C.,  until  the  filtrate  ceases  to 
give  a  blue  colour  with  ferrocyanide  solution.  The  object 
of  leaving  the  residue  for  twelve  hours  is  to  allow  any 
small  particles  of  iron,  remaining  undissolved  by  the  iodine, 
being  oxidised  by  atmospheric  air,  and  prevent  disengage- 
ment of  hydrogen  when  the  hydrochloric  acid  is  added. 
After  the  hydrochloric  acid  is  washed  out  of  the  filter,  it 
is  dried  with  its  contents  at  95°  to  100°  C.,  until  constant 
in  weight.  This  weighing  gives  the  amount  of  the  carbo- 
naceous residue  and  silica  (but  not  the  whole  of  the  silica, 
because  some  part  of  it  would  have  been  dissolved),  and 
by  burning  the  carbon  away  and  weighing  the  silica  the 
weight  of  the  carbonaceous  residue  may  be  ascertained. 
The  carbonaceous  residue  may  consist  either  of  graphite 
or  of  the  compound  of  carbon,  iodine,  and  water  already 
mentioned,  if  the  carbon  was  combined  with  the  iron.  To 
ascertain  which  is  the  case,  1  gramme  of  iron  is  dissolved  in 
.15  c.c.  of  hydrochloric  acid  (1-12  density)  in  a  flask  covered 
with  a  watch-glass,  and,  when  the  iron  is  dissolved,  the  solu- 
tion boiled  for  half  an  hour.  All  the  carbon  combined  with 
the  iron  is  disengaged  in  the  form  of  carburetted  hydrogen 
gas,  while  the  graphite  and  silica  remain.  If  the  carbona- 
ceous residue,  left  after  dissolving  the  iron,  comes  in  con- 
tact with  atmospheric  air  before  the  liquid  is  boiled,  it  is  so 
altered  that  it  is  not  dissolved  and  disengaged  as  gas.  The 
graphite  that  remains  after  boiling  the  liquid  is  collected  on 
a  filter  of  known  weight,  washed,  dried,  and  weighed.  It  is 
then  burnt,  and  the  residual  silica  weighed  to  ascertain  the 
quantity  of  graphite.  Very  satisfactory  results  have  been 
obtained  by  this  method.  The  differences  do  not  amount 
to  more  than  (H  per  cent.  When  the  quantity  of  carbon 
to  be  estimated  is  very  small,  more  than  1  gramme  of  iron 
must  be  used  in  the  analysis. 

< '  The  following  plan  is  simpler  than  the  above,  and  may 

z  2 


840  ASSAY   OF    IRON. 

be  used  when  only  the  graphite  is  required.  In  a  beaker 
of  100  c.c.  capacity  mix  4  c.c.  of  sulphuric  acid  and  20 
c.c.  of  water,  and  when  the  heat  produced  by  the  combi- 
nation of  the  water  and  the  acid  has  entirely  disappeared, 
shake  2  grammes  of  finely  powdered  pig-iron  into  the 
dilute  acid  and  boil  for  half  an  hour.  (For  steel  and 
wrought-iron  not  less  than  3  grammes  should  be  taken, 
and  the  acid  for  solution  increased  in  proportion.)  The 
solution  is  then  evaporated  until  it  measures  18  c.c., 
allowed  to  cool  down  to  the  temperature  of  50°  C.,  and  4 
c.c.  of  nitric  acid,  sp.  gr.  1'20,  added  ;  boil  for  a  quarter  of 
an  hour,  and  allow  to  evaporate  on  a  water-bath,  until,  on 
holding  a  watch-glass  over  the  beaker,  there  occurs  upon  it 
no  perceptible  condensation.  To  the  dry  mass  add  30  c.c.  of 
water  and  5  c.c.  of  hydrochloric  acid,  sp.  gr.  1*16,  boil  for  a 
quarter  of  an  hour,  and  add  more  hydrochloric  acid  if  there 
appears  to  be  anything  besides  silica  and  graphite  remaining 
undissolved.  The  insoluble  silica  and  graphite  are  thrown 
on  a  filter,  which  has  been  dried  at  100°  C.  and  carefully 
weighed,  washed  with  cold  water  until  the  washings  give 
no  iron  reaction  when  tested  with  ferrocyanide  of  potas- 
sium ;  then  washed  with  boiling  water  containing  5  per 
cent,  of  nitric  acid.  The  silica  and  graphite  are  then  dried . 
on  the  filter  at  100°  C.,  and  weighed,  ignited  in  a  porcelain 
crucible,  and  the  weight  carefully  taken.  The  difference 
between  the  weights  before  and  after  ignition  gives  the 
amount  of  the  graphite. 

Mr.  Tosh  gives  the  following  process  for  the  estimation 
of  graphite.  Tw^o  to  three  grammes  of  iron  are  treated 
with  dilute  hydrochloric  acid,  and  when  the  solution 
approaches  completion  a  considerable  quantity  of  strong 
acid  is  added  to  separate  the  last  portions  of  iron  and 
manganese.  The  insoluble  matter,  consisting  mostly  of 
graphite,  is  collected  on  a  carefully  weighed  filter,  washed 
with  hot  water,  dilute 'hydrochloric  acid,  solution  of  caustic 
soda,  and  hot  water  again,  successively,  and  lastly  with 
alcohol  and  ether  to  remove  oily  hydrocarbons.  (By  wash- 
ing with  dilute  acid  and  with  alkali,  the  iron  and  silica  or 
oxide  of  silicon  are  separated.)  After  drying  at  120°  C., 


ESTIMATION   OF   COMBINED    CAKBON.  341 

the  filter  and  graphite  are  weighed,  and  burned  away. 
The  small  residue  (a  mere  trace  of  silica  or  titanic  acid)  is 
weighed,  and  this  weight  subtracted  from  the  first  gives 
the  amount  of  graphite.  The  results  obtained  agree  very 
closely. 

In  washing  the  graphite  with  solution  of  soda,  there  is 
always  a  brisk  effervescence,  due  to  the  oxidation  of  oxide 
of  silicon  to  silicic  acid,  by  decomposition  of  water,  with 
consequent  liberation  of  hydrogen. 

C.  Estimation  of  Combined'  Carbon. — When  steel,  or 
pig-iron  containing  carbon  in  chemical  combination,  is  dis- 
solved in  nitric  acid,  a  soluble  brown  colouring  matter  is 
formed,  whose  colouring  power  is  very  intense,  and  the 
solution  assumes  a  tint  which  is  dark  in  proportion  to  the 
quantity  of  the  chemically-combined  carbon.  Iron  and 
graphite  (or  free  carbon)  do  not  influence  this  colouration  ; 
for  the  solution  of  nitrate  of  iron  is  only  slightly  greenish, 
unless  extremely  concentrated,  and  graphite  is  insoluble  in 
nitric  acid. 

Thus,  in  dissolving  two  pieces  of  different  steels  of  the 
same  weight  in  nitric  acid,  taking  care  to  dilute  the  darker 
solution  until  the  two  liquids  present  exactly  the  same 
colour,  it  is  very  evident  that  the  more  highly  carburetted 
steel  will  furnish  the  larger  quantity  of  liquid,  and  that  the 
proportion  of  the  volumes  will  indicate  the  relative  pro- 
portion of  colour  in  the  two  steels.  If  now  the  composi- 
tion and  content  of  carbon  of  one  of  the  steels  is  known, 
the  absolute  percentage  of  carbon  in  the  other  steel  may 
be  immediately  deduced.  Dr.  Eggertz  has  applied  these 
reactions  to  a  method  of  estimating  the  combined  carbon.  To 

o 

obtain  trustworthy  results  certain  precautions  must  be  taken. 
In  a  cylindrical  test-tube,  dissolve  gradually  in  the  cold, 
10  centigrammes  of  wrought-iron,  steel,  or  cast-iron, 
reduced  to  a  fine  powder,  in  H  to  5  c.c.  of  nitric  acid  of 
1-2  sp.  gr.  The  use  of  nitric  acid  containing  hydrochloric 
acid  must  be  avoided,  because  the  solution  of  iron  would 
have  a  yellow  tint.  In  proportion  as  the  metal  contains  more 
carbon,  more  nitric  acid  must  be  used.  After  some  time, 
when  the  chief  part  of  the  metal  appears  to  be  attacked, 


342  ASSAY    OF   IRON. 

place  the  tube  in  a  water-bath,  and  warm  it  to  80°  C.,  in 
such  a  position  that  only  the  lower  part  of  the  tube  is  in 
contact  with  the  warm  water  ;  a  movement  takes  place  in 
the  acid,  which  favours  its  reaction  upon  the  metal ;  a 
slight  disengagement  of  carbonic  acid  from  all  the  particles 
of  carbon  may  be  observed.  The  operation  should  always 
be  conducted  under  the  same  circumstances  as  to  heat  and 
length  of  time.  The  evolution  of  gas  having  ceased  (in 
operating  upon  steel,  the  reaction  must  continue  two 
or  three  hours),  place  the  tube  in  a  large  vessel  filled  with 
water,  to  bring  the  solution  always  to  the  same  temperature. 
This  precaution  is  indispensable,  because  the  same  liquid  is 
darker  when  warm  than  when  cold.  Afterwards,  pour  off, 
as  exactly  as  possible,  the  clear  liquid  into  a  graduated 
burette.  Upon  the  black  residue  remaining  in  the  tube 
pour  some  drops  of  nitric  acid,  and  heat  carefully  over  a 
lamp.  If  there  is  no  further  liberation  of  gas,  the  residue 
consists  of  nothing  but  graphite  or  silica.  Cool  the  new 
solution,  and  add  it  to  that  which  is  already  in  the 
burette. 

The  liquid  is  then  diluted  with  water  until  its  colour 
corresponds  exactly  with  that  of  .the  normal  liquid,  which 
latter  should  be  of  such  a  degree  of  concentration  that 
each  c.c.  represents  0-0001  grm.  of  carbon.  If,  for  instance, 
this  normal  liquid  is  prepared  from  cast-steel  containing 
exactly  0*85  per  cent,  of  carbon,  1  decigramme  of  that 
steel  must  be  dissolved  in  8*5  c.c.  of  nitric  acid  ;  100  grms. 
of  steel  containing  85  centigrammes  of  carbon  would  thus 
be  dissolved  in  8500  c.c.  of  the  normal  solution,  100  c.c. 
of  that  solution  would  represent  1  centigramme  of  carbon, 
and,  consequently,  1  c.c.  of  the  normal  solution  would 
represent  0*0001  grm.  of  carbon.  To  compare  the  normal 
solution  with  the  solution  of  iron  under  examination,  it 
should  be  contained  in  a  tube  of  the  same  kind,  and  when 
the  two  tubes  are  held  together  by  daylight  before  a  thin 
sheet  of  paper,  the  colour  should  be  exactly  the  same 
in  both  of  them.  As  the  normal  solution  alters  slightly 
in  colour  by  keeping,  and  begins  to  become  paler  after 
twenty- four  hours,  it  is  not  possible  to  keep  such  a  solution 


ESTIMATION   OF   COMBINED    CARBON.  343 

for  use  in  a  tube  hermetically  sealed.  A  solution  of  burnt 
sugar*  in  weak  alcohol  gives  a  solution  of  exactly  the  same 
shade  of  colour  as  the  normal  solution,  and  maintains  its 
colour  for  a  considerable  time  when  protected  from  the 
light.  But  the  best  plan  is  to  make  the  solution  fresh,  as 
it  is  required,  by  dissolving  0*1  gramme  of  steel,  contain- 
ing a  known  amount  of  carbon,  in  5  c.c.  nitric  acid,  and 
diluting  it  to  the  requisite  degree,  which  may  be  indicated 
by  a  mark  upon  the  tube  corresponding  to  the  percentage 
of  carbon  in  the  steel.  If  an  iron  solution  exactly  the 
same  colour  as  the  normal  solution  is  diluted  with  one- 
tenth  its  bulk  of  water,  the  colour  becomes  distinctly 
paler,  so  that  the  delicacy  of  the  method  may  be  judged 
of  from  this. 

Several  modifications  of  this  method  have  been  proposed. 
The  most  successful  of  them,  affording  exceedingly  accurate 
results,  was  communicated  to  the  '  Journal  of  the  Franklin 
Institute,'  for  May,  1870,  by  J.  Blodget  Bntton,  and  has 
been  tested  for  a  considerable  time.  Instead  of  a  single 
tube,  containing  a  standard  solution  for  comparison,  as 
suggested  by  Eggertz,  a  number  of  tubes  having  their 
solutions  differently  standardised,  one  from  the  other,  are 

FIG.  92. 


I 


a 


I 


employed.  These  are  arranged  securely  in  a  wooden 
frame,  with  places  between  for  placing  the  tube  containing 
the  solution  to  be  tested,  and  forming  together  a  convenient 
portable  instrument  called  a  colorimeter  —  a  representation 
of  such  an  instrument  being  shown  in  the  annexed  cut. 
The  position  of  the  tube  containing  the  solution  to  be  tested 
is  shown  at  A.  The  tubes  are  ^ths  of  an  inch  in  diameter, 

*  Slightly  burnt  sugar  gives  a  yellow  solution  ;  highly  burnt  sugar  gives  a 
brown  solution,  but  by  mixing  these  solutions  the  right  colour  may  be  obtained. 


344  ASSAY   OF    IRON. 

and  3|  inches  in  length,  filled  with  water  and  alcohol 
coloured  with  roasted  coffee,  and  hermetically  sealed.  The 
solution  in  the  tube  to  the  left  has  its  colour  to  correspond 
exactly  with  one  produced  by  1  grm.  of  iron,  containing 
0-02  per  cent,  of  combined  carbon,  dissolved  in  15  c.c.  of 
nitric  acid.  The  solution  in  the  tube  next  to  it  has  its 
colour  to  correspond  with  one  produced  by  the  same  quan- 
tity of  iron,  but  containing  0'04  per  cent,  of  combined 
carbon,  and  so  with  each  of  the  other  tubes,  increasing 
0*02  per  cent,  of  carbon  in  regular  succession  to  the  right, 
the  last  reaching  0'3  per  cent.,  as  indicated  by  the  figures 
^on  the  upper  rail  of  the  instrument.  On  the  back  of  the 
instrument,  and  for  the  purpose  of  partially  screening  the 
light  and  allowing  the  different  shades  of  colour  to  be  dis- 
tinctly discerned,  there  is  tightly  stretched  between  the 
rails  some  fine  white  parchment  paper.  This  screen  is  not 
shown  by  the  cut,  but  it  serves  a  very  important  purpose. 
The  process  is  conducted  as  follows : — 1  grm.  of  the  finely 
divided  metal  is  put  into  a  tube  of  about  1^  inches  in 
diameter  and  10  inches  long,  and  digested  for  fifteen  or 
twenty  minutes  in  10  c.c.  of  nitric  acid  of  a  little  more 
than  1-20  sp.  gr.,  free  from  chlorine,  The  solution  is  then 
cautiously  poured  into  a  beaker,  and  a  small  portion  of 
metal  which  remains  undissolved  and  adheres  to  the  bottom 
of  the  tube,  is  treated  with  5  c.c.  of  fresh  acid,  exposed  to 
a  gentle  heat  till  completely  dissolved,  and  added  to  the 
other.  The  contents  of  the  beaker,  when  sufficiently  cool, 
are  filtered  through  two  thicknesses  of  German  paper  (not 
previously  moistened,  and  of  a  diameter  not  exceeding  4^- 
inches)  into  a  tube  about  5  inches  long  and  of  precisely 
the  same  diameter  as  those  in  the  instrument.  After  the 
filtered  solution  has  remained  for  some  minutes  at  the  tem- 
perature of  the  atmosphere,  and  its  colour  become  fixed, 
the  tube  is  placed  in  the  instrument  and  the  carbon  deter- 
mined by  a  comparison  of  shades  :  the  determination  may 
be  made  readily  as  close  as  O'Ol  per  cent.  Heat  should 
not  be  applied  in  the  first  instance  to  facilitate  the  solution 
of  the  metal,  because  a  high  temperature  is  apt  to  cause  a 
slight  loss  of  colour.  Two  thicknesses  of  paper  are  taken , 


ESTIMATION    OF    COMBINED   CARBON.  345 

because  one  alone  is  liable  to  break  ;  and  the  paper  should 
be  used  dry,  for,  if  previously  wetted,  the  water  will 
weaken  the  colour  of  the  solution  ;  and  it  ought  to  be  cut 
to  a  size  not  exceeding  4^  inches,  to  prevent  undue  absorp- 
tion. If  the  metal  to  be  examined  contains  more  than 
0-3  per  cent,  of  carbon,  0*5  grm.,  or  less  of  it,  may  be 
taken,  or  the  solution  may  be  diluted  with  an  equal  volume 
or  more  of  water  and  the  proper  allowance  made  :  or  an 
instrument  of  higher  range  may  be  used.  On  the  other 
hand,  if  the  metal  contains  a  very  small  percentage  of 
carbon,  2  grms.  of  it  may  be  taken.  For  preparing  the 
standard  solutions  (the  normal  ones  begin  to  lose  colour 
after  some  hours),  caramel  dissolved  in  equal  parts  of 
water  and  alcohol,  as  suggested  by  Eggertz,  answers  well; 
but  with  roasted  coffee  as  the  colouring  matter  the  true 
shades  may  be  obtained. 

Dr.  Dingier  has  investigated  this  process,  and  gives  it 
as  his  opinion  that  Eggertz's  process  is  only  applicable 
when  the  same  quantities  and  qualities  of  raw  materials 
are  continuously  applied  for  the  production  of  cast-iron  ; 
but  the  test  fails  to  give  good  results  with  iron  and  steel 
of  different  origin,  since  it  has  been  found  that  the  pre- 
sence of  other  substances — viz.,  sulphur,  copper,  phos- 
phorus, and  silicium — affect  the  accuracy  of  the  test. 

Mr.  E.  E.  Taylor  has  devised  the  following  improve- 
ment upon  the  method  of  Prof.  Eggertz  for  the  determina- 
tion of  combined  carbon  ('  Chemical  News,'  April  2, 1874). 

A  balance,  consisting  of  a  very  fine  thread  of  glass,  with 
a  pan  in  two  parts,  one  a  cup  and  one  a  cone,  serves  to 
weigh  the  steel.  A  horizontal  drill,  with  a  glass  tube  to  form 
a  hopper,  makes  and  conducts  the  drillings  of  steel,  as  they 
are  made,  to  the  balance  pan,  which  is  properly  supported 
about  one-eighth  of  an  inch  above  a  point  to  which  it 
settles,  when  a  two-hundred-milligramme  weight  is  placed 
in  the  pan.  Being  thus  set,  a  sample  of  steel  is  placed  in 
the  drill  lathe,  the  drillings,  as  before  mentioned,  falling 
into  the  pan  below.  As  soon  as  the  two-hundred-milli- 
gramme weight  is  in  the  pan,  the  pointer  sinks  to  the 
index,  when  the  drill  is  stopped.  By  passing  a  tube 


346  ASSAY   OF   IRON. 

through  a  hole  in  the  balance  table,  the  lip  of  the  tube 
offering  a  support  for  the  balance  cup,  while  the  cone  is 
pressed  down  with  a  pair  of  tweezers,  the  drillings  at  once 
fall  into  the  tube,  and  are  ready  for  treatment  with  acid. 

A  glass  funnel  is  made  with  a  capillary  opening  at  the 
contracted  lower  end.  This  is  fused  to  a  "f  tube,  the 
lateral  branch  of  which  is  passed  through  the  window  of 
the  laboratory  to  remove  the  fumes.  A  rubber  nipple 
is  placed  on  the  lower  end  of  the  T  tube,  into  which  the 
tube  containing  the  steel  is  inserted.  Three  c.c.  are  now 
drawn  into  the  funnel  tube,  and  fall  in  drops  upon  the 
steel  below.  At  the  expiration  of  this  action  the  tube  is 
transferred  to  a  bath  kept  at  the  temperature  of  130°  C. 

At  the  end  of  twenty  minutes  from  drawing  in  the 
acid,  the  operation  is  completed  ;  the  whole  of  the  carbon 
has  entered  into  a  clear  yellow  solution,  which  has  a  depth 
of  colour  proportionate  to  the  amount  of  combined  carbon 
in  the  steel.  The  tubes  are  cooled  down  to  a  normal  tem- 
perature, and  compared  with  a  series  of  standard  colours, 
when  it  is  easy  to  read  off  the  amount  of  combined  carbon 
in  a  given  sample  of  steel. 

Estimation  of  Sulphur  in  Iron  and  Steel. — The  plan 
usually  adopted  is  to  dissolve  a  weighed  quantity  (about 
3  grms.)  of  the  metal  in  strong  nitric  acid,  adding  a  little 
hydrochloric  acid  occasionally,  and  evaporating  the  solu- 
tion to  dryness.  Dissolve  the  residue  in  very  dilute  warm 
hydrochloric  acid,  and  precipitate  the  sulphuric  acid  in 
the  solution  by  means  of  chloride  of  barium.  If  the  pre- 
cipitated barium  sulphate,  after  washing  once  or  twice  by 
decantation,  has  a  yellow  or  brown  colour,  owing  to  the 
presence  of  iron  mechanically  carried  down,  heat  it,  before 
filtering,  with  dilute  hydrochloric  acid. 

Dr.  Eggertz,  to  whom  analytical  chemistry  is  indebted 
for  the  colorimetric  process  of  estimating  combined  carbon 
in  iron  and  steel,  has  deviled  an  equally  expeditious  plan 
for  estimating  the  sulphur.  He  takes  one  decigramme  of 
cast-iron,  wrought-iron,  or  steel,  cut  up  or  pulverised,  and 
passed  through  a  sieve  with  holes  not  larger  than  0*6  m.m., 
and  introduces  it,  by  means  of  a  glass  or  glazed  paper 


ESTIMATION   OF   SULPHUR.  347 

funnel,  into  a  flask  about  0-15  metre  high  and  5  centimetres 
diameter,  previously  containing  1  grm.  of  water  and  0*5 
grm.  of  concentrated  sulphuric  acid  ;  or,  in  preference, 
1*5  grm.  of  sulphuric  acid,  sp.  gr.  1*25,  and  whose  volume 
(1-5  c.c.)  has  been  marked  on  the  flask.  A  piece  oi 
polished  silver  plate  (18  m.m.  long,  7'5  m.m.  wide,  and  1 
m.m.  thick,  with  a  hole  at  one  end),  composed  of  75  per  cent, 
of  silver,  25  per  cent,  of  copper,  and  attached  to  a  thin 
platinum  or  silver  wire,  is  quickly  introduced  into  the 
flask,  so  that  it  may  be  a  little  below  the  neck  ;  a  cork  is 
put  in  so  as  to  hold  the  wire  without  completely  closing  it. 
It  is  allowed  to  stand  fifteen  minutes  at  the  ordinary  tem- 
perature, and  the  silver  plate  is  then  removed.  If  the  iron 
contains  sulphur,  the  plate  is  coloured  by  the  sulphuretted 
hydrogen  gas  disengaged  during  the  solution  of  the  iron 
in  the  dilute  sulphuric  acid  ;  and,  according  to  the  amount 
of  sulphur  present,  the  colouration  of  the  plate  passes  to 
a  coppery  yellow,  a  bronze  brown,  a  bluish  brown,  or  a 
blue.  These  colourations  are  determined  with  the  greatest 
accuracy — especially  that  of  the  silver  plate  alone,  No.  1 ; 
that  of  coppery  yellow,  No.  2  ;  that  of  bronze  brown,  No. 
3 ;  that  of  blue,  No.  4.  The  intermediate  degrees  may  be 
represented  by  decimals,  thus :  2- 5  if  the  colouration  is 
between  2  and  3  ;  3'1  if  the  plate  is  one-tenth  towards  the 
blue  ;  3-5  if  it  is  as  much  blue  as  brown  ;  3*9  if  the  brown 
colouration  is  feeble. 

As  the  normal  colouration  No.  2,  Dr.  Eggertz  has 
adopted  that  of  the  bronze  called  yellow  metal,  newly  rubbed 
with  fine  sand  on  leather.  (This  metal  consists  of  60  parts 
of  copper  and  40  of  tin.)  For  the  colouration  No.  3,  a 
convenient  alloy  has  not  yet  been  found.  A  bronze,  con- 
sisting of  85  parts  of  copper  and  15  parts  of  zinc,  does  not 
quite  represent  the  colour  which  should  be  obtained,  for 
when  freshly  cleaned  it  is  too  bright,  and  at  last  takes  a 
bluish  colouration.  For  the  colour  in  question  it  is  better 
to  use  a  plate  of  silver  which  remains  in  the  flask  during 
the  solution  of  the  iron,  until  it  has  become  as  brown  as 
possible,  and  a  slight  bluish  colour  begins  to  be  perceived ; 
the  plate  is  then  removed  and  preserved  in  a  well-closed 


348  ASSAY   OF   IKON. 

tube.  The  colour  No.  4  resembles  that  of  a  watch-spring. 
If  the  amount  of  sulphur  is  very  considerable,  this  coloura- 
tion passes  to  a  clear  bluish  grey.  By  passing  the  plate  of 
silver  over  a  bottle  of  sulphide  of  ammonium  the  desired 
number  can  be  easily  obtained.  To  obtain  in  these  assays 
for  sulphur  the  proper  tint  on  a  silver  plate,  it  is  necessary 
to  take  certain  precautions.  The  plate  is  to  be  held  in 
pincers  and  cleaned  as  well  as  possible  by  rubbing  it  with  a 
soft  leather  on  which  is  placed  a  little  fine  rotten-stone. 
Contact  with  the  fingers  is  avoided  by  means  of  a  piece  of 
paper,  and  the  plate  is  to  be  carefully  dried  with  a  piece  of 
filtering  paper.  If  the  plate,  by  cleaning  or  by  the  action 
of  the  burnisher,  has  been  purified  on  its  surface,  this  should 
be  carefully  removed  by  again  rubbing  with  the  leather,  for 
pure  silver  is' less  sensitive  to  the  action  of  the  gas  than  that 
of  the  given  standard.  Thus  it  has  sometimes  been  found 
that  the  silver  employed  for  coinage  furnishes  less  homoge- 
neous plates,  of  which  those  parts  richest  in  copper  assume 
more  quickly  the  blue  colouration.  On  this  account,  the 
plates  should  be  compared  between  themselves,  by  intro- 
ducing them  at  the  end  of  a  wire  into  a  flask  in  which  iron 
is  dissolving  containing  from  0-05  to  0-08  per  cent,  of  sul- 
phur. On  introducing  the  plate,  care  must  be  taken  not  to 
turn  the  side  but  the  edge  against  the  strongest  current  of 
gas,  which  would  otherwise  colour  one  face  of  the  plate 
stronger  than  the  other.  The  plate  should  be  rapidly  in- 
troduced into  the  flask  after  the  introduction  of  the  iron,  as 
then  a  very  strong  disengagement  of  sulphuretted  hydrogen 
immediately  takes  place.  After  a  first  experiment  the  flask 
is  to  be  filled  with  water  several  times,  so  as  to  get  rid  of 
the  odour  of  sulphuretted  hydrogen.  If  a  steel  mortar  is 
employed  to  pulverise  the  iron,  the  whole  of  the  piece 
selected  should  be  reduced  to  a  very  fine  powder.  The 
mortar  should  be  well  cleaned  each  time,  taking  care  to 
remove  the  disc  from  the  bottom.  Changes  in  temperature 
between  15°  and  25°  C.  seem  to  have  no  sensible  influence  on 
the  colouration  of  the  metal ;  if  the  temperature  exceeds 
40°  the  plate  becomes  moist  and  gives  false  indications. 
Some  practice  is  required  to  judge  of  the  colouration  of 


ESTIMATION   OF   SULPHUR.  349 

the  plate,  but  it  may  be  easily  acquired.  Generally  the 
best  plan  is  to  place  the  standard  plates  of  tints  1,  2,  3, 
&c.,  on  a  sheet  of  white  paper  by  the  side  of  the  plate 
under  experiment,  exposing  them  to  a  good  light  near  a 
window  (but  not  sunlight),  and  to  examine  them  with  a 
lens.  The  colourations  between  2  and  4  are  the  most 
difficult  to  recognise ;  but  with  a  little  experience  none 
will  vary  more  than  O'l,  so  that,  for  instance,  the  coloura- 
tion may  be  estimated  between  3'5  and  3 -6. 

The  following  is  somewhat  an  approximation  between 
the  different  colourations  upon  the  silver  plate,  and  the 
amount  of  sulphur  in  a  great  number  of  different  samples 
of  iron : — 

Number  of  Percentage 

the  Colonration  of  Sulphur 

1-0  0-00 

1-2  0-01 

2-0  0-02 

2-5  0-03 

3-0  0-04 

3-1  0-05 

3-2  0-06 

3-3  007 

3-5  0-08 

3-6  0-09 

37  0-10 

3-8  0-12 

3-9  0-15 

4-0  0-20 

It  is  evident  that  in  this  way  the  exact  quantity  of  the 
sulphur  is  not  determined ;  but  several  years'  experience 
has  shown  that  if  these  experiments  are  made  with  care, 
and  the  quantity  of  sulphur  does  not  exceed  O'l  per  cent., 
the  results  are  near  enough  for  all  practical  purposes. 
Iron  which  does  not  colour  the  silver  plate  will  sometimes 
produce  a  colouration  if  we  double  the  quantities  of  iron 
and  acid.  With  half  the  quantities  of  acid  and  sulphurised 
iron,  silver  generally  gives  a  little  more  than  half  the  real 
quantity  of  the  sulphur  which  is  present. 

Amongst  experiments  on  the  estimation  of  sulphur  in 
iron,  the  following  deserve  mention  : — 1.  The  quantity  of 
sulphur  in  wrought  iron  is  often  so  small  that  it  produces 
no  colouration  on  the  silver  plate  ;  this  iron,  therefore,  not 
being  red-short,  may  be  employed  for  all  kinds  of  uses.  It 


350  ASSAY   OF   IROX. 

must  not,  however,  be  forgotten  that  the  quantity  of  sul- 
phur is  not  equally  distributed  throughout  a  piece  of  iron, 
but  that  it  may  vary  considerably  in  different  places.  On 
experimenting  with  the  turnings  obtained  from  a  portion 
of  an  iron  bar  which  was  visibly  red-short,  a  stronger  tint 
is  often  obtained  on  the  silver  plate  than  when  using  other 
parts  of  the  bar.  The  fragments  obtained  from  red-short 
iron  in  boring  a  horse-shoe  do  not  often  give  on  the  silver 
plate  a  deeper  colouration  than  2,  and  it  appears  to  follow 
that  ordinary  wrought-iron  which  contains  0*02  per  cent, 
of  sulphur  in  certain  parts  cannot  conveniently  be  em- 
ployed for  this  purpose.  If  the  red-short  iron  gives  to  the 
plate  a  slighter  and  more  feeble  colouration  than  2,  it  may 
be  supposed  that  the  breaking  is  due  less  to  sulphur  than 
to  an  insufficient  working  of  the  cast-iron,  the  crude  pieces 
in  wrought-iron  entirely  free  from  sulphur  often  acting  as 
if  they  were  red-short.  In  general  it  appears  certain  that 
the  quantity  of  sulphur  in  iron  is  more  injurious  when  the 
iron  has  been  badly  worked.  In  a  hard  iron  melted  in  a 
steel  crucible  we  may,  in  spite  of  its  containing  0*04  per 
cent,  of  sulphur,  make  holes  like  those  in  a  horse-shoe 
without  any  trace  of  cracks,  which  may  undoubtedly  be 
attributed  to  the  homogeneity  and  good  working  of  this 
iron  ;  the  quantity  of  phosphorus  being*  only  0'03  per 
cent.  The  lower  portion  of  an  English  rolled  rail,  without 
fault,  contained  O'll  per  cent,  of  sulphur  and  0*3  per  cent, 
of  phosphorus ;  a  portion  was  cut  off  which  was  so  red- 
short  that  it  could  not  be  made  use  of. 

2.  The  richness  in  sulphur  of  steel  of  the  best  quality 
is  such  that  the  colourations  on  the  silver  plate  vary  only 
between  1  and  1-5.     As  in  the  case  of  wrought-iron,  the 
quantity  of  sulphur  often  varies  in  different  parts  of  the 
same  piece  of  steel,  and  that  also  appears  to  be  the  case  in 
a  little  less  decided  manner  in  cast-steel. 

3.  The  quantity  of  sulphur  in  cast-iron  is  rarely  so  little 
as  not  to   colour  the  plate.     In  the  greater  number  of 
Swedish  cast-irons,  this  quantity  is  such  that  the  silver 
plate  varies  in  colouration  between  2  and  3.     In  iron  for 
gun-castings   it  is   between   3-3  and  3 '7,  and  sometimes. 


ESTIMATION   OF   SULPHUR.  351 

more.  In  cast-iron  the  quantity  of  sulphur  is  often  dis- 
tributed unequally  ;  there  is  generally  more  on  the  surface 
than  is  met  with  below.  If  the  colouration  of  the  silver 
plate  does  not  exceed  3,  we  can  assume  that  the  cast-iron 
refined  in  the  ordinary  manner  will  not  give  red-short 
iron,  especially  if  the  refining  is  done  carefully.  But  as  in 
different  methods  of  refining  different  quantities  of  sulphur 
may  be  removed  from  the  iron,  and  in  general,  more  if  the 
iron  is  the  result  of  a  light  charge  of  the  blast  furnace,  it 
cannot  be  said  beforehand  that  all  cast-iron  which  communi- 
cates a  bluish  colouration  to  the  plate  will  necessarily  give 
red-short  iron.  This  will  be  the  case,  however,  with  cast- 
iron  which  colours  the  plate  as  deep  a  blue  as  that  of  a 
watch-spring.  In  cast-iron,  which  gives  a  red-short 
wrought-iron,  without  rendering  the  silver  plate  more 
than  brown,  it  is  probable  (the  iron  having  been  well  re- 
fined) that  the  cause  is  owing  to  the  presence  of  other 
substances  than  sulphur,  but  this  occurrence  is  very  rare. 
Many  circumstances  appear  to  show  that  the  quantity  of 
sulphur  in  iron  diminishes  with  time,  at  least  on  the  surface, 
and  under  favourable  conditions. 

The  quantity  of  sulphur  in  a  mineral  cannot  be  esti- 
mated in  the  manner  just  described ;  all  that  can  be  done 
is  to  estimate  the  sulphur  in  the  cast-iron,  which  is  ob- 
tained by  reducing  the  mineral  in  a  crucible.  Attention 
must  always  be  paid  to  the  following :  a.  That  the  pow- 
dered charcoal  which  fills  the  crucible  is  free  from  sulphur. 
This  is  ascertained  by  fusing  iron,  as  free  as  possible  from 
sulphur,  in  a  crucible  filled  with  the  same  powdered 
charcoal,  and  then  examining  the  regulus  obtained.  If 
this  latter  gives  a  higher  amount  of  sulphur  than  the  iron 
originally  contained  the  cause  is  attributable  to  the  char- 
coal. At  Fahlun,  the  charcoal  absorbs,  in  a  short  time, 
much  sulphur  from  the  smoke  of  the  burning  pyrites  ;  and 
the  powder  selected  for  the  crucible  experiments  in  the 
Mining  School  is  obliged  to  be  kept  in  closed  vessels.  If 
the  charcoal  employed  as  a  combustible  in  the  crucible 
furnace  is  exposed  to  the  action  of  much  sulphuretted 
hydrogen  or  sulphurous  acid,  the  experiments  show  it. 


352  ASSAY   OF   IRON. 

b.  The  state  of  the  mineral,  whether  imroasted,  badly 
roasted,  or  well  roasted.  The  small  laboratory  experi- 
ments, having  for  their  object  to  ascertain  how  much 
sulphur  can  be  removed  from  a  mineral  by  roasting  in  bulk, 
are  always  inexact,  c.  The  influence  exerted  on  the  quan- 
tity of  sulphur  by  the  minerals  mixed  with  it.  It  follows, 
from  many  experiments  made  at  the  Mining  School,  that 
the  more  silicic  acid  the  slag  contains  the  more  sulphur 
the  cast-iron  receives,  and  that  the  quantity  of  sulphur 
gradually  diminishes  in  proportion  as  the  quantity  of  lime 
is  increased.  In  general,  assays  for  sulphur  should  be 
made  with  regulus  obtained  from  a  mixture  containing  as 
little  lime  as  possible,  but  giving  vitreous  slags.  If  the 
colouration  of  the  silver  plate  does  not  exceed  No.  3,  the 
quantity  of  sulphur  may  be  considered  as  insignificant, 
especially  in  experimenting  on  non-roasted  minerals. 

The  lime  used  in  blast  furnaces  may  be  assayed  for 
sulphur  in  the  following  manner : — Mix  0-8  gramme  of 
rich  and  pure  iron  ore  with  O2  gramme  of  quartz  and 
0-2  gramme  of  lime ;  fuse  the  mixture  as  usual  in  a  cru- 
cible, and  assay  the  resulting  iron  for  sulphur.  In  this 
manner  it  may  be  ascertained  if  the  lime  contains  an  in- 
jurious dose  of  sulphur.  If  it  were  chemically  pure  we 
should  obtain,  by  the  addition  of  2  or  3  per  cent,  of  clay 
or  talc,  free  from  sulphuric  acid,  a  better  slag.  If,  on  the 
contrary,  the  lime  contains  much  silicic  acid,  more  than 
O2  gramme  should  be  taken  for  the  experiment. 

Dr.  T.  M.  Brown,  in  a  paper  read  before  the  American 
> Institute  of  Mining  Engineers  (February  28, 1874),  remarks 
that  the  method  usually  employed  in  accurate  determina- 
tion of  sulphur  in  pig-iron  and  steel  is  to  treat  a  weighed 
sample  of  borings  in  a  flask  with  hydrochloric  acid,  and  to 
pass  the  gaseous  products  through  an  alkaline  solution  of 
lead  or  silver,  which  precipitates  all  the  sulphur  of  the 
sulphuretted  hydrogen  in  the  form  of  lead  or  silver  sul- 
phide. The  sulphide  thus  formed  is  subsequently  oxidised 
by  aqua  regia,  bromine,  or  other  oxidising  agent,  and  the 
sulphuric  acid  formed  precipitated  in  the  usual  way  by 
barium  chloride. 


ESTIMATION   OF   SULPHUR.  353 

Mr.  Brown  has  substituted  for  the  alkaline  metallic 
solution  a  solution  of  potassium  permanganate  of  the 
strength  of  1  gramme  of  permanganate  to  200  c.c.  of  water, 
and  finds  that  it  gives  results  quite  as  accurate  as  those 
obtained  by  using  an  ammoniacal  solution  of  silver.  By 
the  employment  of  the  permanganate,  it  will  be  readily 
seen  that  there  is  a  considerable  saving  of  time  and  work. 
In  order  to  test  the  accuracy  of  the  method,  six  samples 
of  pig-iron  borings  were  weighed  out  (about  six  grammes 
each),  and  treated  identically  in  the  same  way,  with 
the  exception  that  with  three  an  ammoniacal  solution  of 
silver  was  used,  and  with  the  remaining  three  a  solution 
of  potassium  permanganate.  The  silver  sulphide  formed 
was  filtered  and  oxidised  by  bromine  water.  The  residues, 
after  treatment  with  hydrochloric  acid  in  a  flask,  were  in- 
variably filtered  off  and  washed,  then  evaporated  twice  to 
dryness  with  aqua  regia,  taken  up  with  hydrochloric  acid, 
filtered,  and  the  filtrate  added  to  the  main  solution  contain- 
ing the  solution  of  permanganate.  The  gas  then  gives  not 
the  slightest  blackening  when  passed  into  a  lead  or  silver 
solution.  After  the  evolution  of  gas  has  completely  ceased, 
and  air  has  been  drawn  through  the  apparatus  for  some 
time,  the  contents  of  the  bottles  are  poured  into  a  beaker, 
rinsed  out  with  water,  and  any  manganese  oxide  adhering 
to  the  sides  or  to  the  tubes  dissolved  in  a  little  hydrochloric 
acid.  Enough  hydrochloric  acid  is  then  added  to  the  beaker 
to  completely  decompose  the  permanganate  and  convert 
it  into  a  clear,-  colourless  solution,  in  which  the  sulphuric 
acid  may  be  directly  precipitated.  If  the  solution  does  not 
become  perfectly  clear,  owing  to  impurities  in  the  per- 
manganate used,  filtration  is  necessary  before  precipitation. 

Mr.  C.  H.  Piesse  places  in  a  beaker  of  about  300  c.c. 
capacity  about  3*5  to  4  grins,  of  the  sample  in  drillings 
(weighed  to  within  O'Ol  grm.  will  be  sufficiently  accurate), 
and  pours  upon  them  35  to  40  c.c.  of  aqua  regia,  con- 
sisting of  1  part  HN03  with  two  parts  HC1,  maintaining 
the  proportion  of  10  c.c.  of  the  mixed  acids  for  every 
1  grm.  of  the  metal,  keeping  the  beaker  covered  as  well 
as  possible  with  a  clock-glass.  After .  the  first  violence  of 

A  A 


354  ASSAY   OF   IROX. 

the  action  has  subsided  boil  the  liquid  for  a  few  moments 
until  the  whole  of  the  iron  is  dissolved,  then  transfer  the 
solution,  with  as  little  washing  as  may  be,  to  a  porcelain 
basin,  and  evaporate  as  nearly  as  possible  to  dryness  on  a 
water-bath.  Treat  the  residue  with  some  concentrated 
hydrochloric  acid,  add  about  an  equal  bulk  of  water,  and 
then  filter.  To  the  filtrate  add  a  considerable  excess  of 
solution  of  barium  chloride,  allow  to  stand  for  about 
twelve  hours ;  filter  and  weigh  the  precipitated  barium 
sulphate  with  the  usual  precautions.  Multiply  the  weight 
of  barium  sulphate  found  by  13*724,  and  divide  the  pro- 
duct by  the  weight  of  the  iron  employed ;  the  result  will 
be  the  percentage  of  sulphur  in  the  sample  analysed. 

Mr.  T.  J.  Morel!  (Chemical  News,  October  31, 1874)  pro- 
poses to  acton  the  metal  with  hydrochloric  acid,  and  passes 
the  evolved  gases  through  an  ammoniacal  solution  of  cad- 
mium oxide.  The  precipitate  of  cadmium  sulphide  obtained 
is  collected  on  a  small  filter,  dried  at  212°  F.  and  weighed. 

Estimation  of  Sulphur  in  Iron  Ores. — Five  grammes 
of  the  mineral,  ground  as  finely  as  possible  in  an  agate 
mortar,  are  treated  with  potassium  chlorate  and  hydro- 
chloric acid.  After  desiccation  and  extraction  with  hydro- 
chloric acid  and  water,  the  insoluble  substances  may  be 
lead,  calcium,  barium,  and  strontium  sulphates,  silica,  and 
undecom posed  mineral.  By  stirring  well  and  filtering  the 
liquid  whilst  warm,  the  two  former  salts  may  generally, 
however,  be  dissolved.  The  filtration  should  be  performed 
through  a  double  filter,  to  prevent  the  pulverised  mineral 
from  passing  through.  When  the  clear  portion  of  the 
solution  has  been  poured  upon  the  filter,  add  to  the  in- 
soluble matter  5  c.c.  of  hydrochloric  acid  and  5  (i.e.  of 
water  ;  then  leave  the  mixture  for  two  hours  on  the  water- 
bath  at  a  boiling  temperature,  when,  if  care  be  taken  to 
stir  well,  the  calcium  sulphate  will  be  completely  dissolved. 
Wash  the  insoluble  portion  in  warm  water,  and  pour  it  on 
a  filter,  taking  care  to  place  below  a  flask  specially  to 
receive  that  portion  of  mineral  which  may  have  passed 
through  the  filter.  The  filtered  liquid,  whose  volume  is 
about  50  c.c.,  should  be  rapidly  boiled  and  mixed  with 


ESTIMATION   OF   SULPHUR.  355 

2  c.c.  of  a  saturated  solution  of  barium  chloride.  (This 
amount  is  sufficient  to  precipitate  the  sulphuric  acid 
formed  from  O'l  grm.  of  sulphur.)  After  cooling  add  to 
the  mixture  5  c.c.  of  ammonia  sp.  gr.  0'95,  then  stir  well 
with  a  glass  rod,  and  leave  the  whole  to  rest  at  the  ordi- 
nary temperature  for  twenty-four  hours.  The  clear  solu- 
tion should  be  decanted  as  completely  as  possible  on  to  a 
strong  filter,  and  the  precipitate  stirred  up  with  about  20 
c.c.  of  cold  water,  and  then  left  to  itself  until  it  has  quite 
settled.  If  warm  water  is  used  without  having  added  a 
few  drops  of  hydrochloric  acid,  a  little  oxide  of  iron  will  be 
precipitated.  The  clear  liquid  is  likewise  thrown  on  to  the 
filter,  and  the  operation  is  repeated  several  times  with  cold 
water,  and  then  two  or  three  times  with  boiling  water, 
without  which  precaution  the  barium  sulphate  will  pass 
through  the  filter.  Finally  collect  the  precipitate,  and 
wash  it  with  warm  water.  The  last  drops  of  this  water, 
on  being  evaporated  on  a  watch-glass,  ought  not  to  leave 
more  than  a  scarcely  visible  white  ring.  The  precipitate 
is  then  dried,  heated  to  redness,  and  weighed.  If  it  is 
coloured  with  iron  oxide  it  must  be  washed  with  a  little 
hydrochloric  acid,  dried  in  the  water-bath,  and  taken  up 
with  a  few  drops  of  acid  and  water,  and  then  the  pre- 
ceding operation  repeated  (washing,  drying,  heating,  and 
weighing).  If  the  precipitate  has  only  a  feeble  red  colour, 
which  is  often  the  case,  this  latter  operation  will  be  un- 
necessary. 

To  dissolve  the  lead  sulphate  which  may  occur  in  the 
insoluble  portion,  remove  this  from  the  filter  with  the  end 
of  a  feather,  introduce  it  into  a  flask,  and  pour  over  it 
10  c.c.  of  concentrated  ammonium  acetate.  The  solution, 
after  having  been  strongly  agitated  and  heated  in  the 
water  bath,  is  carefully  poured  on  to  a  filter.  Then  wash 
the  residue  with  a  little4  ammonium  acetate,  and  repeat 
the  treatment  until  a  few  c.c.  of  solution,  acidulated  with 
a  little  acetic  or  hydrochloric  acid,  is  not  rendered  turbid 
when  warmed  with  barium  chloride  solution.  The  fil- 
trate is  then  diluted,  slightly  acidified,  and  the  sulphuric 
acid  precipitated  by  means  of  barium  chloride.  After  the 

A   A   2 


356  ASSAY   OF   IRON. 

lead  sulphate  has  been  removed,  there  may  still  occur 
barium  and  strontium  sulphates  in  the  insoluble  portion, 
To  decompose  these  salts  the  residues  must  be  dried, 
heated  to  redness,  and  weighed,  and  then  fused  with  five 
times  their  weight  of  pure  dry  soda.  The  mass  is  digested 
with  water  over  a  water-bath,  the  liquid  filtered,  and  the 
residue  washed  with  warm  water.  The  silicic  acid  is 
separated  from  the  solution,  which  contains  the  silicate, 
the  sodium  carbonate,  and  sulphate,  by  adding  hydro- 
chloric acid  and  drying  on  the  water-bath.  After  filter- 
ing, precipitate  the  solution  with  barium  chloride.  To 
ascertain  if  the  iron  mineral  contains  gypsum  or  other 
soluble  sulphates,  take  5  grammes,  place  them  in  20  c.c. 
of  hydrochloric  acid  and  60  c.c.  of  distilled  water,  and 
digest  them  for  three  hours  on  the  water-bath,  with 
frequent  agitation.  The  filtered  solution  is  mixed  with 
barium  chloride  and  15  c.c.  of  ammonia ;  then  proceed  as 
already  described.  If  there  are  present  in  the  mineral 
grains  of  iron-  or  copper-pyrites,  or  galena,  they  will  only 
give  traces  of  sulphuric  acid  in  this  operation. 

Estimation  of  Silicon  in  Iron  and  Steel. — All  who  are 
occupied  in  the  analysis  of  iron  and  steel  are  aware  how 
very  uncertain  the  determination  of  silicon  is  when  the 
method  hitherto  used  for  its  separation  is  followed,  because 
cast-iron,  and  even  bar  iron  and  steel,  are  never  found 
absolutely  free  from  intermingled  slag.  This  slag  is  de- 
composed by  the  ordinary  method  of  dissolving  the  iron 
in  acids,  and  its  silica  then  augments  the  amount  of  silica 
formed  from  the  silicon  contained  in  the  iron  or  steel. 
This  cannot  be  said  of  every  sort  of  cast-iron,  but  these 
sometimes  contain  blast-furnace  slag,  although  pig-iron 
containing  slag  may  be  considered  as  rare.  It  ought  also 
to  be  mentioned  that  crystallised  silicon  has  been  found 
in  crystallised  cast-iron  from  Krain,  in  the  form  of  small 
silvery  plates,  which  were  neither  acted  upon  by  boiling 
aqua  regia  nor  by  ignition  in  oxygen  gas  ;  but  they  were 
converted  into  silica  by  fusing  with  potassium  and  sodium 
carbonates. 

Crystallised    silicon  is   insoluble   in   hot    solutions   of 


ESTIMATION   OF   SILICON.  357 

sodium  carbonate,  but  is  soluble,  with  development  of 
hydrogen,  in  hot  solutions  of  caustic  potash,  and  also  in 
hot  hydrofluoric  acid.  The  accurate  determination  of  the 
silicon  in  iron  and  steel  has  been  effected  by  Dr.  Eggertz, 
who,  after  fruitless  efforts  to  dissolve  iron  in  highly  diluted 
organic  or  inorganic  acids,  which  should  have  no  effect  on 
the  refinery  slag,  finally  discovered  such  a  solvent  in 
bromine,  which,  when  mixed  with  water,  dissolves  the 
iron  without  the  slightest  action  on  the  accompanying  slag. 
But  as  experimenting  with  bromine  in  large  quantities  is 
very  disagreeable,  trials  were  made  to  use  iodine  instead  ; 
and  this,  like  bromine,  has  been  proved  to  have  no  effect 
on  the  slag,  nor  on  iron  oxide  or  proto-sesquioxide,  or 
manganese  proto-sesquioxide.  At  the  same  time,  bromine 
dissolves  iron  quicker  than  iodine  does,  and  is,  perhaps, 
more  easily  obtainable  in  the  requisite  state  of  purity. 
Moreover,  as  continued  experiments  have  shown  that  a 
solution  of  sodium  carbonate  can  separate  finery  slag  from 
the  silica  which  has  been  formed  by  the  use  of  iodine  or 
bromine  on  the  silicon  contained  in  the  iron,  the  follow- 
ing method  for  the  determination  of  silicon  and  slag  in 
bar  iron  or  steel  has  been  used  and  considered  successful ; 
the  same  method  may  be  employed  for  cast-iron,  because 
blast-furnace  slag,  when  such  is  found,  is  not  perceptibly 
changed  by  iodine  or  bromine,  nor  by  solutions  of  sodium 
carbonate.  Three  grammes  of  bar  iron  or  steel  which 
has  passed  through  a  sieve  of  0*2  of  a  line  are  taken  for 
analysis.  Fifteen  grammes  of  iodine  are  added  in  small 
portions  at  a  time  to  15  c.c.  of  water  in  a  beaker  of  100 
c.c.  capacity.  The  water  must  be  previously  boiled  to 
expel  the  air,  which  would  otherwise  oxidise  the  iron. 
The  iodine  is  stirred  in  the  water  with  a  glass  rod,  in  order 
to  get  rid  of  the  air  which  has  accompanied  it,  and  the 
floating  iodine  particles  are  allowed  to  sink.  The  beaker 
with  the  iodine  and  water,  which  is  kept  covered  with  a 
watch-glass,  is  cooled  in  ice  before  the  iron  is  put  in,  and 
during  the  solution  it  is  kept  at  the  temperature  of  0°  C. 
For  the  first  few  hours  it  must  be  well  stirred  every  hour, 
or  oftener,  with  a  glass  rod,  but  afterwards  not  so  fre- 


358  .;      ASSAY   OF    IRON. 

quently.     In  consequence  of  the  low  temperature  and  the 
careful  admixture  of  the  iron  (by  which  heat  is  prevented), 
the  solution    may   be    performed  without   the   least  de- 
velopment  of    gas,    and  the  iron   has   less  tendency   to 
become  oxidised  by  the  air  when  at  this  low  tempera- 
ture.     By  pressure,    and  by   agitating   with     the    glass 
rod,  the  solution   of   the    iron    particles    which    collect 
at  the  bottom  of  the  beaker  is  much   facilitated  ;  if  no 
lumps  of  iron  particles  are  visible,  the  beaker   may  be 
kept  at  the  ordinary  temperature,   or,  preferably,  in  ice 
water.     If  some  of  the  solution  has  dried  on  the  sides  of 
the  beaker  or  on  the  glass  rod,  it  must  be  well  moistened 
with  the  same  solution  before  water  is  added.     About  30 
c.c.  of  water,  which  should  be  very  cold  in  order  to  pre- 
vent the  formation  of  basic  salts,  are  added  to  the  solution ; 
it  is  then  well  stirred,  left  to  settle,  and  the  fluid  with  the 
lighter  particles  of  graphite  is  poured  on  to  a  filter  of  2 
in.  diameter  ;  the  filtration  is  kept  up  without  interruption 
until  there  remains   only  a  somewhat  heavy  dark  powder 
of  slag,  &c.  at  the  bottom  of  the  beaker ;  about  5  c.c.  of 
water,  with  a  few  drops  of  hydrochloric   acid,   are  now 
poured  in  and  stirred  with  the  glass  rod  ;  if  hydrogen  is 
given  off,  it  is  an  indication  that  there  is  still  some  metallic 
iron  undissolved.     The  acidified  water  is  quickly  poured 
on  the  filter,  in  order  not  to  act  on  the  slag.     If  a  de- 
velopment of  gas  is  perceived,  a  little  iodine,  with  sodium 
carbonate  and  water,  is  added  for  the  complete  solution 
of  the  iron,  and   the  residue  is  thrown  on  the  filter  and 
washed  with  cold  water,  until  a  drop  of  the  filtrate  gives 
no  reaction  with  a  solution  of  0*2  per  cent,  of  potassium 
ferrocyanide    contained    in    a   small    porcelain   crucible. 
Solutions  containing  0- 00001  gramme  of  ferric  oxide  per 
c.c.  show  in  this  wa^  very  distinct  reactions,  particularly 
if  a  drop  of  dilute  nitric  or  hydrochloric  acid  be  added. 
The  filtrate  is  evaporated  to  dryness,  in  which  operation 
some  of  the  iodine  is  sublimed   away.     Thirty  c.c.  of  hy- 
drochloric   acid,   1-12  sp.  gr.,  are  then  added,  and  it  is 
again  evaporated  in    order  to   obtain    the   silica   which 
may  be  dissolved  in  it.     The  filter,  previously  dried  and 


ESTIMATION   OF   SILICON.  359 

weighed,  is  again  dried  and  weighed  when  containing  the 
precipitate.  It  is  then  ignited,  and  the  residue  weighed. 
After  ignition,  the  residue  is  boiled  in  a  solution  of  soda, 
in  order  to  extract  the  silica,  and  weighed.  It  should  be 
observed  that  some  part  of  the  silica  which  has  been 
formed  from  the  silicon  in  the  iron  may  possibly  unite 
with  the  slag  during  the  drying  and  ignition.  In  conse- 
quence of  this,  it  is  difficult  to  extract  it  by  means  of  a 
soda  solution,  whence  this  method  is  not  to  be  recom- 
mended in  exact  determinations  of  silicon.  . 

When  using  bromine  as  a  solvent  6  c.c.  must  be  taken 
to  3  grammes  of  finely  powdered  iron  or  steel,  with  60  c.c. 
of  water,  which  has  been  previously  boiled  and  cooled  to 
0°  C.  ;  and  this  temperature  must  be  preserved  by  placing 
the  beaker  in  ice  water  until  the  solution  is  complete, 
which  usually  takes  place  in  two  or  three  hours  ;  it  is 
cautiously  stirred  once  or  twice  with  a  glass  rod  ;  if  stirred 
hastily,  the  solution  proceeds  too  violently.  The  further 
operations  are  conducted  in  the  same  manner  as  when 
using  iodine.  The  bromine  is  most  conveniently  preserved 
under  water,  and  is  taken  up  by  a  pipette,  which  is  in- 
troduced into  the  bottle,  the  upper  end  being  kept  closed 
by  the  finger. 

When  it  is  preferred  to  dissolve  iron  or  steel  in  lumps, 
instead  of  in  powder,  this  may  be  done  ;  but  it  is  not  then 
necessary  to  place  the  beaker  mice  water,  as  the  metal  is 
less  violently  acted  upon  in  this  forau  Several  days  are 
required  for  the  solution ;  the  iron,  and  particularly  the 
pieces  of  steel,  must  be  occasionally  cleaned  from  the 
graphite  which  adheres  to  their  surface: 

In  order  to  determine  the  silica  (formed  from  the  silicon 
in  the  iron)  and  slag,  the  filter,  which  contains  graphite  (in 
combination  with  iodine  or  bromine  and  water),  silica,  and 
slag,  is  unfolded,  whilst  it  is  still  wet,  on  a  watch-glass. 
The  contents  are  washed  away  from  the  filter  (these  should 
only  occupy  the  lower  half  of  the  filter  whilst  in  the 
funnel)  with  a  very  fine  jet  from  a  wash-bottle  (so  as  not 
to  obtain  too  much  water)  into  a  platinum  or  silver  crucible 
of  the  capacity  of  30  c.c.  The  loosening  of  the  mass  may 


360  ASSAY   OF    IRON. 

be  facilitated  by  a  fine  camel-hair  brush.  The  water  in 
the  crucible  is  evaporated  to  about  6  c.c.,then  mixed  with 
3  c.c.  of  a  saturated  solution  of  sodium  carbonate,  free 
from  silica,  and  the  crucible  put  in  a  water-bath.  It  is 
kept  in  the  boiling  water  1  hour,  during  which  time  the 
liquid  is  stirred  two  or  three  times,  and  the  insoluble  mass 
crushed  with  a  platinum  spatula.  The  supernatant  liquid 
is  carefully  poured  from  the  insoluble  mass  on  to  a  small 
filter,  and  to  the  mass  in  the  crucible  are  added  1  c.c.  of 
saturated  solution  of  sodium  carbonate,  and  2  c.c.  of  water. 
When  this  has  been  boiled  1  hour,  the  whole  contents  of 
the  crucible  are  thrown  on  the  filter  and  washed.  The 
solution  of  silica  in  soda  Is  acidified  by  hydrochloric  acid, 
and  mixed  with  the  iron  solution,  and  the  whole  evaporated 
to  dry  ness  on  a  water-bath.  When  the  solution  attains 
the  thickness  of  ordinary  syrup,  it  is  stirred  very  often 
with  the  glass  rod,  until  the  mass  becomes  a  dry  powder, 
and  heated  until  the  smell  of  hydrochloric  acid  has  nearly 
gone  off;  the  beaker  is  then  placed  in  boiling  water  for 
6  hours,  15  c.c.  of  hydrochloric  acid  of  1-12  sp.  gr.  are 
then  added,  and  the  beaker  left  on  the  water-bath  1  hour. 
As  soon  as  the  red  powder  is  entirely  dissolved  50  c.c.  of 
water  are  added  ;  and  when  no  crystals  of  iron  chloride 
are  visible,  the  solution  is  thrown  on  a  filter  and  washed 
with  cold  water,  warm  water  forming  basic  iron  salts  which 
make  the  silica  appear  red.  The  filter  containing  the  silica 
is  dried  and  ignited  in  a  porcelain  crucible,  gradually  in- 
creasing the  temperature  to  a  full  red  heat,  and  weighed  ; 
if  the  silica  is  coloured  red  by  ferric  oxide,  a  little  hydro- 
chloric acid,  1-19  sp.  gr.,  must  be  poured  into  the  crucible. 
One  decigramme  of  ignited  and  pure  silica  obtained  from 
analysis  will  dissolve  in  the  above  manner  in  6  c.c.  of  a 
saturated  soda  solution,  and  12  c.c.  of  water.  If  any 
residue  is  observed  after  the  second  boiling,  this  arises 
from  some  impurity  which  has  united  in  small  quantities 
with  the  silica,  rendering  it  insoluble.  When  strong  hy- 
drochloric acid  is  boiled  with  this  insoluble  silica,  it  may 
afterwards  be  dissolved.  When  the  solution  of  silica  is 
diluted  with  water  to  the  volume  of  50  c.c.  at  the  ordinary 


ESTIMATION    OF    SILICON.  361 

temperature,  it  has  no  tendency  to  come  into  the  form  of 
jelly.  Quartz  powder  is  dissolved  by  the  preceding 
method,  but  very  slightly,  but  ignited  titanic  acid  and 
finery  slag  are  not  acted  upon,  and  the  tersilicate  slag  from 
blast-furnaces  but  very  little. 

When  the  silica  is  quickly  exposed  to  a  high  tem- 
perature a  considerable  loss  may  arise  from  the  spirting  of 
the  water  combined  with  the  silica.  Silica  dried  at  100°  C. 
has  been  proved  to  retain  1  equivalent  of  water  to  3 
equivalents  of  silica,  that  is,  about  6  per  cent,  of  water, 
which  is  lost  by  a  strong  ignition.  The  ferric  oxide  is  easily 
dissolved  in  the  heat  of  a  water-bath.  The  silica  is  again 
thrown  on  a  filter,  washed,  dried,  ignited,  and  weighed. 

To  ascertain  the  purity  of  the  silica,  it  may  be  mixed, 
in  a  platinum  crucible  with  ten  times  its  weight  of  pure 
ammonium  fluoride,  diluted  with  water  to  the  thickness  of 
syrup.  The  water  must  be  evaporated  on  a  water-bath, 
and  the  crucible  heated,  with  a  cover  on  it,  by  a  gradually 
increasing  heat  over  a  spirit-lamp  to  a  full  red.  If  nothing 
is  left  in  the  crucible,  the  silica  was  pure,  and  has  passed 
off  as  silicon  fluoride  ;  but,  if  anything  remains,  the  opera- 
tion with  ammonium  fluoride  must  be  repeated  until  a 
constant  weight  is  obtained.  When  iron  contains  tungsten, 
some  tungstic  acid  is  formed,  and  this  accompanies  the 
silica  for  the  most  part,  being  dissolved  by  the  soda  solu- 
tion, but  it  is  not  volatilised  by  the  use  of  ammonium 
fluoride.  Yanadic  acid  also  accompanies  the  silica,  behaving 
as  tungstic  acid.  Instead  of  using  ammonium  fluoride,  it  is 
preferable  to  use  hydrofluoric  acid,  with  which  the  silica  is 
moistened,  and  the  evaporation  is  conducted  on  a  water- 
bath.  The  mass  left  on  the  filter  from  the  soda  solution 
may  be  composed  of — besides  graphite — slag,  iron  oxide, 
titanium  oxide,  &c.  (but  not  copper,  at  least  when  the 
iron  does  not  contain  more  than  1  per  cent.) ;  this  is  dried, 
ignited,  and  weighed.  The  method  of  separating  iron 
oxide  and  slag,  when  the  iron  or  steel  contains  both  these, 
is  not  yet  known.  If  the  composition  of  slag  were  always 
alike  (which  it  is  not)  it  would  be  easy  to  calculate  its 
amount  from  either  the  silica  or  iron  oxide  obtained  in 


362  ASSAY   OF   IRCLN\ 

the  analysis.  In  a  piece  of  very  red- short  Bessemer  iron 
which  contained  no  sulphur,  by  several  experiments  0*3 
per  cent,  of  iron  oxide  has  been  obtained,  and  only  traces 
of  silicon.  After  ignition,  the  iron  oxide  may  possibly  be 
found  as  sesquioxide.  The  amount  of  oxygen,  in  case  the 
redshortness  is  due  to  this,  as  it  probably  is,  amounts  to 
less  than  0*1  per  cent. 

When  the  iron  or  steel  for  analysis  contains  titanium,  a 
part  of  this  substance  follows  the  slag  in  the  form  of  titanic 
acid.  If  such  is  the  case,  this  must  be  melted  with  ten 
times  its  weight  of  acid,  potassium  sulphate,  by  which  it 
is  dissolved  ;  the  mass  is  dissolved  in  cold  water,  and  the 
solution  precipitated  by  boiling  ;  the  weight  is  determined, 
and  subtracted  from  that  of  the  slag. 

In  respect  to  the  determination  of  silicon  in  cast-steel 
where  only  a  trace  of  slag  is  found,  the  method  given 
below  for  cast-iron  may  be  employed ;  but  3  grammes  at 
least  ought  to  be  taken  for  each  experiment,  and  the  acids 
for  solution  in  proportion.  The  amount  of  silicon  in  bar 
iron  and  steel  generally  varies  between  0*01  per  cent,  and 
O'l  per  cent.  ;  but  in  two  sorts  of  good  cast-steel  from 
Krupp's  it  has  amounted  to  about  0-3  per  cent.  Slag  in 
cast-steel  has  been  found  only  in  traces,  but  in  another 
case  it  amounted  to  0*2  per  cent. ;  in  good  iron  wire,  pre- 
pared from  bar  iron,  converted  in  a  refinery  hearth,  from 
charcoal  pig-iron,  0'33  percent.  ;  in  puddled  iron  (armour- 
plate),  from  0'75  to  3  per  cent.  ;  and  in  an  English  iron 
rail,  to  4  or  5  per  cent. 

For  the  determination  of  silicon  in  cast-iron,  in  which 
no  finery  slag  is  found,  and  only  exceptionally  blast-fur- 
nace slag,  the  following  method  has  proved  suitable : — 2 
grammes  of  iron,  which  has  passed  a  sieve  with  holes  of  a 
diameter  of  -^  inch  at  the  most,  is  put  into  a  beaker  of 
100  c.c.  capacity  containing  30  c.c.  of  hydrochloric  acid, 
sp.  gr.  1-12.  The  beaker  is  covered  with  a  close-fitting 
watch-glass,  heated  without  delay,  and  the  liquid  kept  in 
gentle  ebullition  for  half  an  hour.  All  the  carbon  chemi- 
cally combined  with  the  iron  is  separated  from  the  liquid 
in  the  form  of  an  ill-smelling  volatile  hydrocarbon.  If  the 


ESTIMATION   OF   SILICON.  363 

carbon  separated  on  solution  is  left  in  contact  with  the 
air  some  minutes  before  ebullition,  it  undergoes  such  a 
change  that  it  does  not  go  off  in  a  volatile  form  ;  if  neces- 
sary some  hydrochloric  acid  is  added,  and  the  solution 
evaporated  to  dry  ness  on  a  water-bath.  When  the  silica 
is  red,  strong  hydrochloric  acid  is  added,  as  previously 
described.  If  the  silica  is  contaminated  with  titanic  acid, 
vanadic  acid,  or  tungstic  acid,  it  is  operated  upon  with  am- 
monium fluoride  or  hydrofluoric  acid,  as  previously  men- 
tioned, whereby  the  silica  is  volatilised  and  calculated  by 
loss.  By  the  above  method  of  dissolving  iron  in  hydro- 
chloric acid,  the  silicon  changes,  without  evaporation,  for 
the  most  part,  to  insoluble  silica,  which  may  be  filtered 
and  determined.  Sometimes  a  very  unimportant  part  is 
dissolved,  especially  if  the  boiling  has  been  insufficient. 
When  iron  is  dissolved  in  hydrochloric  acid  without  heating 
(white  cast-iron  is  very  difficult  to  dissolve  in  this  way),  a 
still  less  portion  of  silicon  is  dissolved,  and  generally  so 
little  that  it  may  be  neglected  for  practical  purposes.  The 
washing  is  performed  with  hot  water  containing  nitric 
acid,  as  previously  described.  When  the  iron  is  dissolved 
in  nitric  acid,  a  great  deal  of  silica  enters  into  solution. 
The  different  sorts  of  cast-iron  appear  to  be  slightly  dif- 
erent  in  this  respect.  In  dissolving  cast-iron  by  the  aid 
of  heat,  in  very  dilute  sulphuric  acid,  a  great  deal  of  silica 
is  dissolved,  but  very  little  when  the  acid  is  strong  ;  as 
the  water  evaporates,  the  silica  separates  and  becomes 
insoluble. 

The  method  given  below  rests  upon  these  circumstances, 
and  has  proved  very  satisfactory,  whilst  the  removal  of  the 
acid  is  avoided,  which  is  both  necessary  and  troublesome 
when  using  hydrochloric  acid  with  heat.  The  amount  of 
silicon  has,  according  to  both  methods,  turned  out  alike. 
Two  grammes  of  cast-iron,  which  have  passed  a  sieve  of 
0-2  of  a  line,  are  shaken  by  smaU  portions  at  a  time  into  a 
beaker  of  100  c.c.  capacity,  previously  containing  18  c.c. 
of  water  with  3  c.c.  pure  sulphuric  acid  of  1-83  sp.  gr., 
with  6  c.c.  of  water.  The  beaker  is  covered  with  a  watch- 
glass,  and  placed  on  a  water-bath  :  if  the  graphite  rises  oo. 


364  ASSAY   OF   IRON. 

the  sides  of  the  beaker,  it  is  pushed  down  into  the  liquid 
by  a  glass  rod.  When  the  iron  is  dissolved,  the  watch-glass 
is  changed,  after  being  washed,  for  a  paper  cover,  and  the 
solution  evaporated  on  a  water-bath  until  no  condensation 
occurs  on  a  watch-glass  held  over  the  beaker :  30  c.c.  of 
water  are  then  added,  and  it  is  frequently  stirred  with  a 
glass  rod,  whilst  on  the  water-bath,  until  the  white  iron 
salt  has  completely  dissolved.  The  insoluble  mass  is  then 
thrown  on  a  filter,  and  washed  with  hot  water  containing 
5  per  cent,  nitric  acid,  1*2  sp.  gr.  (in  order  to  dissolve  all 
compounds  of  iron),  as  long  as  an  iron  reaction  is  given 
with  potassium  ferrocyanide.  The  filter,  with  its  contents, 
is  placed  in  a  carefully  tarred  porcelain  crucible  ;  it  is  then 
cautiously  dried,  ignited,  and  weighed.  The  purity  of  the 
silica  is  examined  by  the  method  previously  mentioned, 
when  considered  necessary.  If  the  cast-iron  contains 
vanadium,  this  is  obtained  for  the  most  part  as  a  yellow- 
brown  vanadic  a.cid  with  the  silica,  from  which  it  may  be 
extracted  by  warm  hydrochloric  acid  or  by  ammonia. 

The  amount  of  silicon  in  grey  charcoal  pig-iron  is  about 
2*7  per  cent,  and  in  spiegeleisen  0-8  per  cent.  The 
amount  of  silicon  in  pig  from  coke  blast-furnaces  is  rarely 
more  than  4  per  cent.  The  least  quantity  of  silicon  in 
grey  cast-iron  is  about  0'2  per  cent.,  and  in  white  (spiegel- 
eisen) O'Ol  per  cent.  The  amount  is  usually  from  1  to  2 
per  cent,  in  cast-iron  suitable  for  the  Bessemer  process, 
and  in  pig-iron  for  puddling  about  0*5  per  cent.  The 
amount  of  silicon  in  iron  of  different  degrees  of  hardness 
from  the  same  charge  of  the  blast-furnace  ought  to  be 
pretty  well  judged  by  the  fracture,  after  some  determina- 
tions have  been  made  by  analysis. 

Estimation  of  Phosphorus  in  Iron  and  Steel. — The  im- 
portance 'of  ascertaining  the  quantity  of  phosphorus  in 
iron  is  very  great ;  for,  although  the  presence  of  a  very 
small  quantity  of  phosphorus  in  cast-iron  does  not  produce 
any  sensible  modification  in  its  properties,  it  nevertheless 
loses  its  most  essential  qualities  when  the  proportion  of 
phosphorus  amounts  to  some  thousandths.  Almost  all  the 
methods  hitherto  proposed  consist  in  treating  cast-iron 


ESTIMATION   OF   PHOSPHORUS.  365 

with  oxidising  agents  in  such  a  manner  as  to  cause  the 
phosphorus  to  pass  into  the  condition  of  phosphoric  acid, 
which  is  estimated  as  a  magnesian  compound.  Several 
sources  of  error  are  inherent  to  this  method,  to  avoid 
which  M.  Tantin  liberates  the  phosphorus  as  an  hydrogen 
compound.  Experiment  shows  that  there  is  not  the  least 
trace  of  phosphorus  in  the  residue  after  the  complete 
attack  of  the  cast-iron  by  hydrochloric  acid,  which  fact  is 
not  surprising  if  it  be  considered  what  strong  affinities 
phosphorus  has  for  hydrogen.  The  hydrogen  phosphide 
produced  by  the  action  of  hydrochloric  acid  upon  cast- 
iron  is  almost  always  accompanied  by  sulphuretted,  arse- 
niuretted,  and  carburetted  hydrogen.  In  order  to  effect 
the  separation  of  these  gases,  first  pass  them  into  a  WoulfTs 
flask  containing  a  solution  of  potash,  which  absorbs  the 
sulphuretted  hydrogen ;  the  other  gases  are  then  made  to 
traverse  a  solution  of  silver  nitrate,  which  transforms  the 
arseniuretted  hydrogen  into  silver  arsenite,  soluble  in  the 
slightly  acid  liquid,  whilst  the  phosphuretted  hydrogen 
precipitates  the  silver  solution  and  forms  an  insoluble  phos- 
phide. The  phosphorus  being  thus  completely  separated 
from  the  sulphur  and  arsenic,  its  estimation  is  effected  in 
a  simple  manner.  The  phosphide  of  silver  is  treated  with 
aqua  regia,  and  thus  transformed  into  silver  chloride  and 
phosphoric  acid,  which  is  precipitated  in  the  state  of  am- 
monio-magnesian  phosphate.  To  get  accurate  results  by 
this  process,  the  following  precautions  are  indispensable  :— 

1st.  The  cast-iron  must  be  attacked  very  slowly,  or 
part  of  the  phosphuretted  hydrogen  may  traverse  the 
solution  of  silver  nitrate  without  being  absorbed. 

2nd.  When  the  solution  of  the  cast-iron  is  finished,  a 
current  of  hydrogen,  previously  washed  in  lead  acetate, 
must  be  passed  through  the  flask. 

Mr.  Tosh  estimates  the  phosphorus  in  the  following 
way :  3  grammes  of  the  iron  are  dissolved  in  aqua  regia, 
the  solution  evaporated  to  dryness.  and  the  insoluble  matter 
filtered  off.  The  ferric  chloride  solution  is  reduced  to  the 
state  of  ferrous  chloride,  by  heating  with  sodium  sulphite. 
Although  perfectly  reduced,  the  solution  still  retains  a 


366  ASSAY   OF    IRON. 

yellow  colour,  due  to  dissolved  organic  matter.  All  excess 
of  sulphurous  acid  is  boiled  off,  a  little  ferric  chloride  is 
added,  and  the  solution  cautiously  neutralised  by  means 
of  sodium  or  ammonium  carbonate,  till  the  precipitate 
formed  does  not  dissolve  again.  This  small  portion  of 
ferric  oxide  contains  all  the  phosphoric  acid.  It  is  filtered 
off,  washed,  re-dissolved  in  a  little  hydrochloric  acid,  and 
the  phosphoric  acid  precipitated  as  magnesium  ammonio- 
phosphate,  the  iron  being  held  in  solution  in  the  ammo- 
niacal  liquid  by  citric  acid. 

Dr.  Noad  says  the  following  precautions  are  needed  to 
ensure  accuracy  when  dealing  with  iron  and  steel  contain- 
ing very  small  amounts  of  phosphorus.  The  solutions 
should  not  be  too  bulky.  When  estimating  phosphorus 
in  iron  and  steel,  from  75  to  100  grains  should  be  taken, 
and  the  solution,  at  the  time  of  adding  the  tartaric  (or 
citric)  acid,  ammonia,  and  magnesium  sulphate,  must  never 
be  allowed  to  exceed  in  volume  3  fluid  ounces.  The  first 
precipitate  always  carries  down  a  little  iron,  which  is  re- 
moved by  re-solution  and  re-precipitation  after  the  addition 
of  a  fresh  small  quantity  of  tartaric  acid.  The  first  pre- 
cipitate must  not  be  collected  till  after  the  liquid  has  stood 
for  twenty-four  hours  ;  the  second  precipitate  is  quite  white, 
and  may  be  filtered  off  after  half  an  hour ;  it  contains  the 
whole  of  the  phosphoric  acid. 

Estimation  of  Manganese  in  Iron. — After  the  silicon 
is  determined  in  the  iron  or  steel  by  Eggertz's  method 
(p.  357),  the  manganese  may  be  estimated  in  the  same 
amount  of  material.  The  filtrate  from  the  silicate  is  diluted 
with  water  until  it  measures  400  c.c.  and  accurately 
divided  into  two  portions  of  200  c.c.  each,  one  of  which  is 
set  on  one  side,  and  in  the  other  the  manganese  is  estimated 
in  the  following  manner : — (In  the  case  of  wrought-iron 
arid  steel,  where  3  grammes  are  taken,  the  solution  is 
diluted  to  200  c.c.,  and  the  manganese  estimated  without 
dividing  the  solution.)  A  saturated  solution  of  sodium 
carbonate  is  added  to  the  solution  until  it  becomes  nearly 
neutralised,  appearing  of  a  deep  brown  colour ;  water 
containing  5  per  cent,  of  sodium  carbonate  is  then  added, 


ESTIMATION   OF   MANGANESE.  367 

drop  by  drop,  until  a  slight  turbidity  occurs  in  the  solu- 
tion ;  and  if,  on  standing  in  the  cold,  this  turbidity  rather 
increases  than  diminishes,  sufficient  carbonate  has  been 
added  (if  too  much  sodium  carbonate  has  been  added,  and 
a  precipitate  is  thrown  down,  the  excess  must  be  neutralised 
by  hydrochloric  acid)  ;  to  the  slightly  turbid  solution  add 
1^  c.c.  of  hydrochloric  acid,  and  heat  on  the  water-bath 
until  the  solution  becomes  clear ;  dilute  with  about  half 
as  much  water  as  the  volume  of  the  solution,  and  add  30 
c.c.  of  a  saturated  solution  of  sodium  acetate,  boil  for  a 
quarter  of  an  hour,  allow  the  precipitated  iron  to  settle, 
and  decant  the  clear  liquid  through  a  filter,  washing  the 
iron  by  decantation  with  boiling  water  containing  ^  per 
cent,  of  sodium  acetate  ;  finally,  throw  the  iron  on  the 
filter,  and  continue  the  washing  until  bromine  water  gives 
no  reaction,  showing  that  all  the  manganese  has  passed 
through  the  filter ;  evaporate  the  filtrate  down  to  400  or 
500  c.c.;  and  at  the  temperature  of  50°  C.  add  a  few  drops 
of  bromine  to  precipitate  the  manganese,  and  keep  it  near 
to  that  temperature  for  twelve  hours,  stirring  occasionally 
with  a  glass  rod ;  the  solution  after  the  addition  of  the 
bromine  becomes  of  a  yellow  or  brownish  colour,  but 
should  be  perfectly  colourless  before  filtering.     The  man- 
ganese is  now  thrown  on  a  filter  which  has  been  dried  at 
100°  C.,  and  accurately  weighed,  washed  with  cold  water 
containing  1  per  cent,  of  hydrochloric  acid,  dried  at  100° 
C.,  and  weighed.     The  precipitate  is  a  hydra  ted  manga- 
nese oxide,  containing  59 -21  per  cent,  of  manganese.     The 
precipitate  may  also  be  ignited  in  a  porcelain  crucible  at 
a  white  heat,  and  is  then  an  anhydrous  manganese  oxide, 
containing   72*05  per  cent,  of  manganese.     If  copper  is 
present  it  must  be  removed  previous  to  the  precipitation 
of  the  manganese ;  or  the  amount  of  copper  found  in  the 
ignited  oxide,  and  then  an  equivalent  amount  of  copper 
oxide,  subtracted  from  the  total  weight  of  the  precipitate. 
In  using  the  first  method,  20    grains    of  the  finely- 
divided  spiegeleisen  are  completely  dissolved  in   hydro- 
chloric   acid,    diluted,    and   a   current   of    sulphuretted 
hydrogen  passed  through  the  liquid.     After  standing  for 


368  ASSAY   OF   IRON. 

twelve  hours,  the  solution  is  filtered  and  washed  with 
water  containing  sulphuretted  hydrogen ;  the  filtrate  is 
boiled,  10  grs.  of  potassium  chlorate  added,  the  iron  sepa- 
rated, and  the  manganese  estimated  in  the  usual  manner. 
If  the  method  used  be  that  of  determining  the  copper  in 
the  precipitate,  the  estimation  must  be  made  with  the 
greatest  care,  on  account  of  the  small  quantity  of  copper 
present ;  the  solution  must  be  decanted  immediately  the 
zinc  is  completely  dissolved,  and  excess  of  acid  must  be 
carefully  avoided,  otherwise  the  film  of  copper  will  par- 
tially re-dissolve.  It  is  evident  that,  if  the  precipitation 
be  effected  by  ammonium  sulphide  or  sodium  carbonate, 
separation  or  estimation  of  the  copper  is  likewise  neces- 
sary. 

Mr.  E.  Eiley  (Chemical  News,  April  27,  1877)  gives  the 
following  instructions  on  the  determination  of  manganese 
in  spiegeleisen,  and  in  many  auriferous  iron  ores  : — 

There  are  two  methods  now  in  use — (a)  The  Direct 
Method. — The  pulverised  spiegeleisen  (about  1  grm.)  is 
dissolved  in  dilute  nitric  acid,  sp.  gr.  1-2,  a  little  potassium 
chlorate  and  hydrochloric  acid  added  to  destroy  the  soluble 
organic  matter  from  the  combined  carbon  ;  the  solution, 
diluted  to  about  a  litre,  is  neutralised  with  sodium  or  ammo- 
nium carbonate,  sodium  or  ammonium  acetate  added,  the 
solution  boiled,  the  basic  iron  peracetate  allowed  to  settle 
and  filtered  off.  This  precipitate  is  re  dissolved  in  hydro- 
chloric acid,  and  the  process  repeated  to  ensure  complete 
separation  of  the  manganese.  The  filtrates  are  evaporated 
to  1|  litres,  allowed  to  cool,  2  to  4  c.c.  bromine  added, 
the  solution  well  shaken,  0*880  ammonia  added  in  excess, 
the  solution  heated  gradually  for  an  hour,  boiled  for  a 
few  minutes,  the  precipitate  allowed  to  settle,  filtered  (the 
filtrate  should  be  evaporated  and  tested  for  manganese), 
dried,  and  ignited  in  a  muffle,  or  over  a  gas  blowpipe  for 
half  an  hour. 

(b)  The  Indirect  Method. — The  finely-powdered  spiegel  - 
eisen  (about  1  grm.)  is  dissolved  in  dilute  sulphuric  or  in 
hydrochloric  acid,  the  liquid  diluted  with  recently-boiled 
and  cooled  distilled  water,  and  the  iron  estimated  volumetri- 


ESTIMATION   OF   MANGANESE.  369 

cally ;  to  the  percentage  of  iron  thus  obtained  5  per 
cent,  is  added  for  carbon  and  impurities ;  the  difference  is 
assumed  to  be  manganese. 

The  results  obtained  by  this  method  are  usually  too  low, 
from  the  formation  of  soluble  organic  matter  during  the 
process  of  solution.  This  error  can  be  obviated  by  using 
nitric  acid  for  a  solvent,  evaporating  to  dryness  and  heat- 
ing ;  the  iron  and  manganese  oxides  are  then  dissolved  in 
hydrochloric  acid,  the  solution  largely  diluted,  and  reduced 
with  sodium  sulphite.  The  results  thus  obtained  agree 
very  closely  with  the  direct  method.  Thus,  for  all  practical 
purposes,  the  indirect  method  is  sufficiently  accurate,  and 
can  be  accomplished  in  one  hour,  the  direct  method  re- 
quiring five  or  six  hours.  The  author  strongly  recom- 
mends the  use  of  ammonium  acetate  and  carbonate,  instead 
of  the  corresponding  soda  salts  in  the  direct  method,  and 
proves  by  check  experiments  with  pure  manganese  sul- 
phate, &c.,  the  statements  of  Fresenius  and  others,  that  the 
presence  of  ammoniacal  salts  prevents  the  complete  pre- 
cipitation of  manganese  by  bromine  and  ammonia,  to  be 
erroneous.  On  the  other  hand,  if  soda  salts  be  used,  the 
ignited  precipitate  will  contain  soda.  The  author  con- 
siders that  sulphur  cannot  exist  in  spiegeleisen.  He  de- 
termines the  carbon  by  dissolving  the  iron  in  neutral 
copper  chloride,  and  after  complete  solution  of  the  iron 
and  precipitated  copper,  the  carbon  is  filtered  on  asbestos, 
and  burnt  with  copper  oxide  in  a  current  of  oxygen. 
The  carbon  determinations  by  the  colour  test  are  unsatis- 
factory for  high  percentages  of  carbon.  According  to  the 
author  the  percentage  of  carbon  varies  with  the  percentage 
of  manganese. 

Estimation  of  Manganese  in  Manganiferous  Iron  Ores. 
These  ores  contain  baryta,  many  contain  zinc  oxide,  and 
some  potash  or  soda  in  appreciable  quantities.  The 
use  of  ammoniacal  salts  as  mentioned  in  the  previous 
part  of  the  paper  prevents  any  large  error  from  the 
presence  of  the  zinc  oxide,  but  it  is  difficult  to  get  rid  of 
the  baryta ;  even  in  the  presence  of  sulphuric  acid  it 
remains  in  combination  with  the  manganese,  and  is  pre- 
15  r, 


370  ASSAY   OP   IRON. 

cipitated  with  it  unless  special  precautions  be  taken.  Lime, 
if  present,  may  also  be  precipitated  with  the  manganese. 
1  grm.  of  the  ore  dried  at  100°  C.  is  dissolved  in  hydro- 
chloric acid,  the  siliceous  matter  separated  by  filtration, 
and  the  larger  portion  of  the  free  acid  driven  off.  The 
liquid  is  made  up  to  about  J  of  a  litre,  and  allowed  to 
stand  for  four  hours,  after  adding  a  few  drops  of  sulphuric 
acid  to  separate  any  baryta.  The  solution  is  now  diluted 
to  about  1  litre,  neutralised  with  ammonia  after  the  ad- 
dition of  ammonium  acetate,  boiled,  allowed  to  settle,  and 
filtered  ;  the  unwashed  precipitate  is  re-dissolved  in  hydro- 
chloric acid,  and  again  precipitated  with  ammonia  and  am- 
monium acetate.  The  basic  iron  peracetate,  after  settling, 
is  filtered  off  and  washed  three  or  four  times  with  boiling 
distilled  water,  containing  a  few  drops  of  ammonium  ace- 
tate. The  filtrate  is  evaporated  to  1^  litres,  when  cold  2 
to  4  c.c.  of  bromine  added,  and  the  process  completed  as 
described  above.  After  ignition  the  precipitate  should 
be  dissolved  in  a  small  quantity  of  hydrochloric  acid,  the 
residue,  if  any,  filtered  off,  a  drop  of  sulphuric  acid  added, 
and  the  precipitate,  if  any  occurs,  separated.  It  is  most 
important  to  test  the  ignited  Mn304  for  impurities,  baryta, 
zinc,  lime,  &c.  Chlorine  can  be  substituted  for  bromine, 
but  without  advantage.  The  ammonium  sulphide  process 
is  considered  to  be  most  objectionable. 

Estimation  of  Iron. — A  standard  solution  of  potassium 
bichromate  is  recommended,  the  results  being  usually  a 
little  high.  As  a  reducing  agent,  sodium  sulphite  prepared 
in  the  laboratory  is  used,  the  purchased  samples  being 
always  impure ;  sodium  bisulphite  should  not  be  used. 
The  percentages  of  iron  in  sixty  samples  of  steel  rails  are 
given,  determined  by  weighing  as  Fe203,  and  by  standard 
solution  of  potassium  bichromate  ;  the  mean  difference 
between  the  two  methods  is  0*073  per  cent. 

The  accurate  determination  of  manganese  in  spiegel- 
-eisen  is  of  importance  commercially  ;  as,  -being  the  most 
important  constituent  the  value  of  the  material  is  fre- 
quently judged  by  the  percentage  of  that  element  alone, 
while  the  error  introduced  by  the  presence  of  copper  is 


ESTIMATION    OF   IRON.  371 

aggravated  by  the  fact  that,  not  only  is  copper  worthless, 
but  absolutely  injurious. 

The  following  method  for  the  assay  of  manganese  in 
iron  and  steel  by  Mr.  Samuel  Peters,  Bay  State  Iron  Works, 
South  Boston,  is  not  new  in  principle,  but  has  given  very 
satisfactory  results : — 

Dissolve  0-1  grm.  pig  iron  or  steel  in  3  or  4  c.c.  nitric 
acid,  about  1*2  sp.  gr.,  and  boil  gently  in  a  long  test-tube 
(about  8  inches  long  and  §-inch  diameter)  for  five  or  ten 
minutes,  or  until  solution  is  complete ;  then  add  an  excess 
of  plumbic  oxide,  say  0-2  or  0'3  grm.,  and  boil  again  two 
or  three  minutes.*  Cool  the  tube  and  its  contents  in  water. 
Filter  through  asbestos,  washing  out  the  test-tube  and  the 
residue  on  the  filter  with  distilled  water  until  all  the  colour 
has  been  washed  through.  Transfer  to  a  graduated  tube 
(|;-inch  in  diameter),  holding  50  or  60  c.c.,  graduated  in 
0-2  c.c.,  and  compare  with  a  standard  solution  of  perman- 
ganate held  in  a  tube  for  that  purpose.  The  comparison 
is  made  in  the  same  manner  as  that  in  the  Eggertz  method 
when  estimating  combined  carbon  in  steel,  &c.  The  solu- 
tion under  comparison  is  then  diluted  and  well  mixed  with 
distilled  water  (by  pouring  the  contents  of  the  graduated 
tube  into  a  small  dish,  and  then  transferring  to  the  tube 
again),  until  its  colour  is  exactly  of  the  same  intensity  as 
the  standard  solution.  Having  attained  to  this  point,  the 
number  of  c.c.  is  noted,  and  the  result  is  obtained  by 
multiplying  each  c.c.  byO'OOOl.  Each  c.c.  is  equivalent  to 
O'Ol  per  cent,  manganese  when  O'l  grm.  of  iron  is  taken 
for  analysis. 

For  irons  containing  O'lO  to  0*35  per  cent,  manganese, 
0-1  grm.  is  the  proper  quantity ;  but  if  there  be  say  0'8  to 
1*00  per  cent.,  it  is  best  to  take  0*1  grm.  and  divide  the 
solution  (before  adding  the  lead  peroxide)  in  four  equal 
parts,  and  use  0'25  for  the  estimation,  taking  another  0'25 
for  a  second  estimation.  In  case  of  a  high  percentage,  as 
1-00  per  cent.,  if  0-1  grm.  is  taken  the  results  are  too  low 
on  account  of  some  of  the  manganese  escaping  oxidation. 

*  It  is  unnecessary  to  filter  off  graphite  in  pig-iron  "before  "boiling  with 
plumbic  oxide. 

B  B  2 


372  ASSAY   OF   IKON. 

This  agrees  with  the  observations  of  others.  With  an  un- 
known iron,  one  or  two  trials  with  O'l  grm.  or  half  that 
quantity  will  point  out  the  probable  amount,  and  so  be  a 
guide  for  the  next  trial.  If  the  amount  of  iron  taken  does 
not  yield  more  colour  than  corresponds  to  25  to  35  c.c. 
of  standard  hue,  it  may  be  safely  said  that  all  the  manga- 
nese is  oxidised.  It  is  as  well  to  take  this  volume  as  the 
guide  to  the  quantity  of  iron  to  be  taken.  The  quantity 
of  manganese  in  the  liquor  to  be  tested  should  not  exceed 
0-4  of  a  milligrm.,  and  certainly  not  over  half  a  milligrm. 
By  taking  0*1  grm.  of  a  spiegeleisen  containing  nearly  12 
per  cent,  manganese,  and  diluting  to  50  c.c.,  and  taking 
2  c.c.  or  O04  for  the  estimation  of  the  manganese,  very 
nearly  the  proper  amount  of  manganese  is  obtained.  This 
seems  to  show  that  if  the  division  of  the  solution  can  be 
accurately  made,  and  the  bulk  of  the  coloured  liquid  can 
be  kept  down  well,  the  amount  of  manganese  in  spiegeleisen 
can  be  estimated  very  fairly. 

Combined  carbon  in  large  quantity  does  not  inter- 
fere with  the  accuracy  of  the  method,  for  a  steel  con- 
taining 2-00  per  cent,  combined  carbon  and  only  O80  per 
cent,  manganese  was  found  to  give  good  results  by  this 
method. 

The  standard  is  made  by  diluting  a  permanganate  of 
potash  solution  of  known  strength  until  each  c.c.  =  0-00001 
grm.  manganese. 

For  example  a  -^  solution  will  contain  3'16  grm.  per- 
manganate in  1000  c.c.  or  O'OOll  grm.  manganese  per 
c.c.;  if  this  be  diluted  110  times  it  will  give  the  required 
strength.  The  standard  is  contained  in  a  tube  of  the  same 
bore  as  the  one  used  for  the  analysis,  or  else  the  standard 
is  put  in  the  latter  one,  and  a  solution  of  permanganate 
put  into  a  tube  of  nearly  the  same  bore,  and  diluted  until 
it  exactly  corresponds  with  the  standard  solution,  when  it 
will  serve  as  a  standard. 

Permanganic  acid  of  the  proper  hue  keeps  better  than 
permanganate  of  potash  of  the  same  hue,  and  is  of  course 
easily  made  by  adding  nitric  acid  to  the  latter.  The  time 
occupied  in  obtaining  a  result  by  this  method  is  very  short 


ESTIMATION   OF   IRON.  373 

(about  half  an  hour),  and  it  is  a  method  that  will  prove 
of  advantage  in  analysing  steel  made  by  the  Bessemer  and 
Siemens-Martin  processes. 

Mr.  Galbraith  ('Chemical  News,'  February  4,  1876) 
has  given  the  following  simple  and  accurate  process  for  the 
assay  of  manganese  in  spiegeleisen  : — 1  grm.  of  the  spiegel- 
eisen  is  dissolved  in  nitric  acid  (sp.  gr.  1*20)  in  a  small 
round-bottomed  flask,  and  evaporated  to  dryness.  When 
dry,  the  flame,  which  may  be  either  a  spirit  lamp  or  a: 
Bunsen  burner,  is  turned  so  that  the  bottom  of  the  flask 
is  cherry-red  for  ten  minutes.  It  is  then  allowed  to  cool 
very  gradually. 

At  this  point  a  weighed  quantity  of  ammonio-ferrous 
sulphate,  or  ferrous  sulphate  of  a  known  strength,  is  put 
into  the  flask,  and  then  heated  with  rather  dilute  hydro- 
chloric acid.  The  contents  of  the  flask  very  soon  dissolve, 
but  it  is  well  to  keep  shaking  the  solution  while  it  is  being 
heated  to  prevent  loss  of  chlorine.  It  only  remains  now 
to  determine  the  iron  left  unoxidised,  in  order  to  arrive 
at  the  quantity  of  manganese,  which  can  be  done  with 
potassium  bichromate  solution.  It  is  feared  that  the  ferrous 
solution  may  get  oxidised  by  exposure  to  the  air  ;  a  small 
piece  of  marble  put  into  the  flask,  which  can  also  be  fitted 
with  a  cork  and  tube,  will  readily  prevent  that. 

In  four  successive  experiments  the  following  results 
were  obtained. 

No.  Pe  Equal  to 

Oxidised  Manganese  p.  c. 

1  0-2018  19-82 

2  0-2103  20-65 

3  0-2396  23-53 

4  0-2435  23-88 

No.  2  gave  by  ammonium  acetate  method  20*55  per 
cent.,  which  was  done  with  great  care.  No.  4  is  a  repeti- 
tion of  No.  3. 

It  is  evident  of  course  that  there  is  nothing  original  or 
new  in  the  above  method  ;  but  it  contrasts  very  favourably 
with  the  usual  methods  of  separating  the  iron  with  sodium 
or  ammonium  acetate,  and  precipitating  the  manganese 
from  the  filtrate  with  bromine.  It  is  not  at  all  trouble- 


374  ASSAY    OF   IRON. 

some,  does  not  take  long,  and  has  the  advantage  that  the 
only  chemicals  and  apparatus  required  are  those  which 
are  necessary  for  the  assay  of  iron  ores. 

Estimation  of  Titanium  in  Iron. — The  detection  of 
titanium  in  iron  is  easy,  although  its  estimation  is  difficult. 
The  best  results  have  been  obtained  by  following  Eiley's 
plan.*  This  is  essentially  as  follows  : — A  weighed  portion 
of  the  iron  borings  are  treated  with  fuming  nitric  acid  in  a 
flask,  a  few  drops  of  hydrochloric  acid  added  from  time  to 
time,  the  whole  being  well  boiled.  The  contents  of  the 
flask  are  then  transferred  to  a  porcelain  dish,  evaporated  to 
dryness,  and  heated  strongly.  On  cooling,  it  will  be  found 
that  the  iron  oxide  readily  detaches  itself  from  the  dish, 
and  can  be  easily  transferred  to  a  beaker,  the  portions 
left  on  the  dish  being  dissolved  in  hydrochloric  acid,  and 
poured  on  the  contents  of  the  beaker ;  the  dish  may  be 
rinsed  out,  if  necessary,  with  strong  hydrochloric  acid. 
The  contents  of  the  beaker  are  boiled  for  from  two  to  three 
hours  until  complete  solution  of  the  iron  is  effected ;  and 
as  some  quantity  of  hydrochloric  acid  is  required  for  this, 
the  best  plan  is  to  allow  a  large  portion  of  the  excess  of 
acid  to  evaporate  in  the  beaker,  retaining  only  as  much 
as  is  requisite  to  keep  the  iron  in  solution.  The  silica 
is  filtered  off  in  the  usual  way,  after  diluting  with  water 
and  adding  a  few  drops  of  hydrochloric  acid  on  the  filter, 
to  dissolve  the  basic  salt  formed  by  the  water.  By  this 
means  the  silica  can  be  obtained  nearly  white  after  burning 
off  the  graphite,  and  very  little  iron  will  be  found  with  it 
unless  much  phosphorus  be  present,  as  the  silica  invariably 
contains  more  or  less  iron  phosphate  from  the  insoluble 
iron  phosphide,  which  cannot  be  completely  dissolved  out 
by  hydrochloric  acid.  Before  determining  the  titanium 
the  residue  from  the  silica  should  be  fused  with  potassium 
bisulphate,  dissolved  in  water  and  added  to  the  solution  of 
iron  in  which  the  titanium  is  to  be  determined.  The  solu- 
tion is  reduced  with  sodium  sulphite,  and  the  excess  of 
sulphurous  acid  is  driven  off  by  boiling.  The  solution  is 
then  nearly  neutralised  with  ammonia,  and  ammonium  or 

*   Chemical  News,  viii.  226,  233. 


ESTIMATION   OF   TITANIUM.  375 

sodium  acetate  added  ;  if  there  is  only  a  small  quantity  of 
phosphoric  acid,  there  will  always  be  sufficient  peroxide 
of  iron  to  precipitate  it,  but  if  not,  a  few  drops  of  nitric 
acid  must  be  added  so  that  the  precipitate  produced  is 
distinctly  red,  and  the  solution  boiled  and  filtered  as 
quickly  as  possible.  The  residue  is  fused  with  potassium 
bisulphate,  or  where  nitric  acid  is  used,  this  is  driven  off 
with  sulphuric  acid.  The  result  of  the  fusion  with  potas- 
sium bisulphate  is  dissolved  in  cold  water  (when  a  little 
iron  phosphate,  which  remains  insoluble,  is  separated), 
boiled  for  some  hours,  and  allowed  to  stand  a  night  in  a 
warm  place,  when  the  titanic  acid  is  filtered  off  and 
Washed  with  dilute  sulphuric  acid,  dried,  ignited,  and 
weighed. 

The  above  process  is  not  very  satisfactory  for  the 
quantitative  determination  of  titanic  acid.  The  iron  phos- 
phate (insoluble  in  the  potassium  bisulphate)  cannot  be 
washed  without  its  passing  through  the  filter,  and  very 
frequently,  also,  the  small  amount  of  iron  keeps  up  the 
titanic  acid,  as  iron  even  in  small  quantities  has  a  very 
great  effect  in  preventing  the  precipitation  of  titanic  acid, 
so  that  it  is  always  advisable  to  add  a  little  sodium 
sulphite,  which  reduces  the  iron  oxide  and  facilitates  the 
precipitation  of  the  titanic  acid. 

Titanium  may,  however,  be  found  more  satisfactorily 
and  more  readily,  during  the  process  usually  adopted  to 
determine  the  amount  of  graphite  in  pig-iron,  provided  a 
large  quantity  of  the  pig  be  operated  on.  About  200 
grains  of  the  pig  are  to  be  dissolved  in  dilute  hydrochloric 
acid  ;  when  the  pig  is  nearly  all  dissolved,  and  the  action  of 
the  acid  has  ceased,  more  hydrochloric  acid  is  added,  and 
the  solution  well  boiled,  so  as  to  thoroughly  extract  all  the 
iron.  The  solution  is  then  thrown  on  dried  counterpoised 
filters  encircling  each  other,  and  the  filter  well  washed  to 
remove  all  the  iron.  It  is  then  treated  with  dilute  potash, 
and  washed  once ;  then  re-treated  with  it  so  as  to  entirely 
remove  the  silica.  The  potash  is  thoroughly  washed  out, 
and  the  filter  treated  with  hydrochloric  acid,  thoroughly 
washed  and  dried  at  250°  F.  until  the  weight  is  constant. 


376  ASSAY   OF    IRON. 

This  gives  the  graphite,  on  burning  which  a  residue  of  a 
dirty  light  brown  colour  is  left,  which,  fused  with  potas- 
sium bisulphate  and  subsequent  treatment  as  above  ex- 
plained, is  seen  to  be  nearly  pure  titanic  acid. 

Mr.  Tosh  advises  the  approximate  estimation  of 
titanium  in  iron  to  be  effected  in  the  following  way : — 
About  6  grammes  of  iron  are  dissolved  in  hydrochloric 
acid,  and  the  whole  evaporated  to  dryness.  The  dried 
mass  is  moistened  with  hydrochloric  acid,  water  added, 
and  the  solution  filtered.  Part  of  the  titanium  exists  in 
the  solution  (a)  and  part  in  the  insoluble  residue  (b).  The 
solution,  if  containing  much  iron  perchloride,  is  reduced 
by  sodium  sulphite,  the  excess  of  sulphurous  acid  boiled 
off,  a  little  iron  perchloride  added,  and  the  titanic  acid 
precipitated  in  combination  with  the  ferric  oxide  thus 
introduced,  by  means  of  sodium  carbonate,  as  in  the 
estimation  of  phosphorus.  The  small  precipitate  is 
quickly  filtered  off,  washed,  dried,  ignited,  and  carefully 
set  aside.  From  the  insoluble  matter  (b)  graphite  is 
burned  off,  and  the  silica  is  removed  by  hydrofluoric  acid 
in  the  presence  of  sulphuric  acid.  To  the  residue  after 
this  treatment  the  small  ferruginous  precipitate  from  (a) 
is  added,  and  the  whole  fused  with  potassium  bisulphate. 
When  cool  the  fused  mass  is  extracted  with  cold  water, 
and  from  the  clear  filtered  solution  titanic  acid  and  iron 
are  precipitated  by  ammonia  ;  the  precipitate  is  slightly 
washed,  -and  ammonium  sulphide  added.  The  iron  sul- 
phide thus  formed  is  dissolved  by  sulphurous  acid,  while 
the  titanic  acid  mixed  with  sulphur  is  undissolved,  ,and 
may  be  collected,  ignited,  and  weighed,  after  which  it 
should  be  tested  as  to  its  purity. 

In  testing  a  siliceous  residue  for  titanic  acid  with 
hydrofluoric  acid  it  must  be  remembered  that  a  titanium 
fluoride  is  formed  at  the  same  time,  which  cannot  be 
heated  without  the  larger  portion  going  off. 

Mr.  W.  Bettell  ('Chem.  News,'  Aug.  22,  1873) 
proposes  the  following  modification  of  Mr.  D.  Forbes' 
process  ('  Select  Methods  in  Chemical  Analysis,'  pp.  110, 
111)  for  the  estimation  of  titanic  acid,  which  may  not  be 


ESTIMATION   OF   TITANIUM.  377 

unacceptable  to  those  engaged  in  the  analysis  of  titanic 
ores  : — 

Fuse  about  0-5  grm.  of  the  finely  powdered  ore  with 
6  grms.  of  pure  potassium  bisulphate  (which  has  been 
recently  fused  and  powdered)  in  a  platinum  crucible  at  a 
gentle  heat,  carefully  increased  to  redness,  and  continued 
till  the  mass  is  in  a  state  of  tranquil  fusion. 

Remove  from  the  source  of  heat,  allow  to  cool^  digest 
for  some  hours  in  5  or  6  oz.  of  cold  distilled  water  (not 
more  than  10  oz.  is  to  be  used,  as  it  generally  causes  a 
precipitation  of  some  titanic  acid)  filter  off  from  a  little 
pure  white  silica,  dilute  to  45  or  50  oz.,  add  sulphurous  acid 
till  all  the  iron  is  reduced,  then  boil  for  six  hours,  replacing 
the  water  as  it  evaporates. 

The  titanic  acid  is  precipitated  as  a  white  powder, 
which  is  now  to  be  filtered  off,  washed  by  decantation,  a 
little  sulphuric  acid  being  added  to  the  wash-water,  to 
prevent  it  carrying  titanic  acid  away  in  suspension.  Dry, 
ignite,  allow  to  cool,  moisten  with  solution  of  ammonium 
carbonate,  re-ignite,  and  weigh.  The  titanic  acid  is 
invariably  obtained  as  a  white  powder,  with  a  faint  yellow 
tinge,  if  the  process  has  been  properly  carried  out. 

This  method  of  fusing  with  potassium  bisulphate 
('  Select  Methods,'  p.  125)  is  preferable  to  all  others  for 
decomposing  difficultly  soluble  iron  ores. 

The  sample,  very  finely  powdered,  is  decomposed 
with  hydrochloric  acid,  and  the  silica  is  separated  in  the 
ordinary  manner. 

In  order  to  oxidise  the  iron  the  solution  is  heated  with 
a  little  potassium  chloride,  and  is  precipitated  whilst  warm 
with  ammonia  in  slight  excess. 

Ferric  oxide  and  alumina  are  thus  precipitated  along 
with  a  part  of  the  magnesia  and  a  little  of  the  lime. 

The  precipitate,  washed,  dried,  and  ignited,  is,  after 
weighing,  ground  up  in  agate  mortar,  and  as  much  of  it 
as  can  be  poured  out  again  is  ignited  anew  and  weighed. 
{This  is  not  the  entire  original  quantity,  some  traces  being 
lost,  a  circumstance  which  must  be  remembered  in  the 
calculation.)  After  this  re-ignition  and  re-weighing,  it  is 


378  ASSAY   OF   IRON. 

rubbed  up  in  a  silver  crucible  with  a  small  quantity  of 
sodium  carbonate,  a  sufficiency  of  caustic  potash  is  added,, 
and  the  covered  crucible  is  heated  very  cautiously  over 
the  lamp.  At  last  the  temperature  of  the  fused  mass  is 
raised  to  redness,  and  kept  so  for  about  a  quarter  of 
an  hour.  When  cold  the  crucible  is  steeped  in  water,  to 
which  a  little  alcohol  is  added  in  order  to  reduce  manganic 
acid ;  the  whole  is  heated  to  a  boil,  filtered,  and  washed 
with  hot  water.  The  residual  ferric  oxide,  together  with 
the  filter,  is  digested  in  hydrochloric  acid,  the  diluted 
solution  is  filtered  and  precipitated  with  ammonia.  The 
filtrate  from  the  ferric  oxide  is  mixed  with  that  from  the 
first  ammoniacal  precipitate.  The  solution  of  alumina  in 
potash  is  faintly  acidified  with  hydrochloric  acid,  care 
being  taken  that  nothing  is  lost  by  the  effervescence  of 
the  liquid,  and  the  alumina  is  precipitated  with  ammonium 
hydro-sulphide  or  ammonium  carbonate,  washed  with  hot 
water,  dried,  ignited,  and  weighed. 

The  filtrate  from  the  ammoniacal  precipitate  is  mixed 
in  a  stoppered  flask  with  ammonium  hydro-sulphide. 

The  precipitate  of  manganese  sulphide  is  allowed  to 
settle,  filtered  rapidly  with  exclusion  of  air,  redissolved 
in  hydrochloric  acid,  and  precipitated  hot  with  sodium 
carbonate.  The  manganous  carbonate  is  converted  by 
ignition  into  mangano-manganic  oxide,  and  weighed  as 
such. 

The  filtrate  from  the  manganese  sulphide  is  faintly 
acidulated  with  hydrochloric  acid,  heated  to  expel 
sulphuretted  hydrogen  and  filtered.  The  lime  is  then 
determined  by  means  of  oxalic  acid  and  ammonia,  and  the 
magnesia  by  sodium  phosphate. 

If  the  proportion  of  manganese  is  large,  larger  perhaps 
than  that  of  the  iron,  as  is  the  case  in  some  blast-furnace 
slags,  the  following  process  is  adopted.  After  the  silica 
has  been  removed,  ammonium  chloride  and  a  little  sodium 
acetate  are  added  to  the  liquid,  which  is  then  heated, 
saturated  with  chlorine  gas,  precipitated  with  ammonia,  and 
boiled  till  the  free  ammonia  has  escaped.  The  precipitate 
which  contains  ferric  and  manganic  oxides  and  alumina,  is 


ESTIMATION   OF   TITANIUM.  379 

filtered  off  and  washed  with  hot  water.  It  is  then 
redissolved  in  hydrochloric  acid,  with  the  addition  of  some 
alcohol,  diluted,  without  filtration,  and  barium  carbonate 
finely  ground  up  in  water  is  added  in  such  quantity  that 
a  portion  of  it  remains  in  excess.  The  whole  is  then 
allowed  to  stand  for  an  hour  with  frequent  stirring.  The 
ferric  oxide  and  alumina,  together  with  the  excess  of 
barium  carbonate,  are  then  filtered  off,  washed  in  cold 
water,  the  baryta  removed  by  means  of  sulphuric  acid, 
filtered,  and  ferric  oxide  and  alumina  are  precipitated  with 
ammonia.  After  ignition  and  weighing  they  are  separated 
as  above  mentioned.  The  manganic  liquid  is  also  freed 
from  dissolved  baryta  by  sulphuric  acid  supersaturated 
with  sodium  carbonate  and  boiled,  thus  determining  the 
manganese. 

From  the  filtrate  of  the  three  bases  the  lime  and  the 
magnesia  are  precipitated  by  well-known  methods. 

A  volumetric  determination  of  the  iron  in  a  separate 
portion  of  the  sample  is  very  valuable  as  a  check.  If  the 
slag  contains  both  ferrous  and  ferric  oxides  this  determi- 
nation is  necessary.  For  this  purpose  the  powdered  slag, 
with  the  addition  of  a  fragment  of  marble,  is  heated  with 
hydrochloric  acid  in  a  small  flask,  and  with  constant  shak- 
ing, till  it  is  completely  decomposed.  Unless  the  ferric 
oxide  is  to  be  reduced  by  zinc,  the  whole  is  poured  into 
an  excess  of  water,  and  determined  with  the  standard 
solution  of  potassium  bichromate. 

If  the  slag  contains  small  proportions  of  lead  or 
copper  they  are  precipitated  with  sulphuric  acid  after  the 
removal  of  the  silica,  filtered,  and  the  liquid  concentrated 
by  evaporation  before  the  iron  is  oxidised.  The  precipi- 
tated sulphides,  which  are  usually  small  in  quantity,  are 
treated  according  to  methods  already  laid  down. 

Small  quantities  of  sulphur  exist  in  many  slags  as 
sulphides,  and  are  determined  in  a  separate  portion  of  the 
sample. 


380 


CHAPTEE  X. 

THE   ASSAY   OF   COPPER. 


IN  the  assay  of  copper  by  the  dry  way,  all  minerals  and 
substances  containing  that  metal  may  be  divided  into 
three  classes. 

CLASS  I.     Comprises  Sulphuretted  Ores  or  Products,  with 
or  without  Selenium,  Antimony,  or  Arsenic. 

Copper  glance,  Cu2S,  containing  797  p.  c.  of  copper 

Chalcopyrite,    Cu2S,  Fe2S3,  „        34'4  „ 

Erubesoite,       3Cu2S,Fe2S3,  „         557  „ 

Bournonite,      3Cu2S,SbS3  +  2(3PbS,SbS3)  „        127  „ 

Fahlerz,  4(Cu2S,FeS,ZnS,AgS,HgS).(SbS3,AsS3,Bi2S8) 

„         30—48  „  „ 

Oovelline,        CuS,  „        667  „ 

Wolfsbergite,  Cn2S,SbS3,  „        24-9  „ 

Domeykite,      Cu6As,  „        71'6  „  „ 

Copper  regulus,  Copper  speiss,  &c. 


CLASS  II.     Oxidised  Ores  and  Products. 

Red  copper,  Cu20,  containing  887  per  cent,  of  copper 

Malachite,    2CuO,  +  H20,  „        67-3  „  „ 

Azurite,       2CuO,CO2  +  CuO.H20  „        55-1  „  „ 

Cyanosite,    CuO,S03    +5H20,  „        25'3  „ 

Phosphate  of  copper,  „       30—56  „  „ 

Arsenkte  of  copper,  „      25  —  50  „  „ 
Chromate,  Vanadate,  and  Silicate  of  Copper  ;  Slags,  &c. 

CLASS  HI.     Copper  and  its  Alloys. 


The  different  methods  of  assaying  copper  are  more  nu- 
merous than  those  for  any  other  metal.  They  are,  in  some 
cases,  very  similar  to  each  other,  and  in  others  based  upon 
very  different  principles. 


CLASSIFICATION   OF   THE   COPPER   ASSAYS.  381 

These   methods   may   be   classified    in   the    following 

manner  : — 

A.  ASSAY  IN  THE  DRY  WAY. 

a.  For  rich  Ores  and  Products  of  Class  I. 

1.  English  Copper  Assay. 

2.  German  Copper  Assay. 

b.  For  poor  Ores  and  Products  of  Class  I. 

1.  Fusion  of  the  ore,  &c.,  to  a  crude  regulus,  and  further  treatment  of  the 

same  according  to  a  2. 

2.  Fusion  of  the  roasted  ore   with   reagents  to  collect   the  copper  (lead, 

antimony,  or  arsenic),  and  refining  the  crude  copper. 

c.  For  Ores  and  Products  of  Class  II. 

1.  Reducing  and  solvent  fusion,  with  or  without  collecting  reagents  (anti- 

mony, arsenic,  lead),  for  the  copper,  after  the  ore  has  been  roasted,  if 
necessary  (in  the  case  of  cyanosite  and  arseniate  of  copper)  with  coal- 
dust,  graphite,  or  ammonium  carbonate. 

2.  Concentration  smelting  with  pyrites  to  a  regulus,  which  is  then  roasted 

and  smelted  to  crude  copper  with  or  without  collecting  reagents  for  the 
copper. 

d.  Copper  and  its  Alloys.     (Class  III.) 

Kefining  with  lead  on  the  cupel,  or  with  borax  on  the  refining  dish,  with  or 
without  the  addition  of  lead,  antimony,  or  arsenic. 

B.  ASSAY  IN  THE  WET  WAY. 


A.  ASSAY  IN  THE  DRY  WAY. 
a.  For  rich  Ores  and  Products  of  Class  I. 

I.    ENGLISH   COPPER   ASSAY. 

M.  L.  Moissenet  has  given,  in  the  'Annales  des  Mines,'* 
a  very  complete  description  of  the  Cornish  method  of 
assaying  copper  by  the  dry  way.  The  following  is  from  a 
translation  by  Mr.  W.  W.  Procter. 

Each  of  the  large  Swansea  copper-works  keeps  an 
assayer  at  Cornwall,  whose  duty  it  is  to  determine  the 
richness  in  copper  of  all  the  lots  of  minerals  in  the  county 
sold  every  Thursday  at  the  Ticketing,  and  of  all  the 

*  Vol.  xiii.  r.  183. 


382  ENGLISH   COPPER   ASSAY. 

samples  of  foreign  minerals  and  copper  products  which 
may  be  useful  to  the  smelter. 

The  copper  being  obtained  in  the  state  of  a  prill  or 
metallic  button,  the  impurities  (generally  tin,  antimony, 
&c.)  are  thus  made  evident,  and  the  hammer  soon  proves 
the  quality  of  the  metal  which  we  ought  to  expect  to 
obtain  by  metallurgic  treatment.  As  for  the  accuracy  of 
the  method,  as  far  as  regards  the  whole  of  the  metal 
obtained,  we  shall  revert  to  this  later  on.  We  would, 
however,  observe  that,  within  certain  limits,  the  method 
would  not  be  less  practical  on  account  of  being  inexact ; 
for  we  must  not  forget  that  it  has  chiefly  for  its  object 
to  teach  the  smelter  the  value  of  the  mineral,  even  more 
than  its  true  richness. 

For  example,  if  we  get  too  low  an  assay  from  a  sample 
of  2  or  3  per  cent.,  we  should  only  from  this  assent  to  the 
opinion  of  the  metallurgist,  whose  interest  it  is  not  to  work 
upon  very  poor  minerals.  The  same  remark  will  apply  to 
the  case  of  minerals  very  antimonial,  &c.  Besides,  in  the 
description  of  the  method  we  shall  discover  the  principal 
phases  of  the  Welsh  process  ;  so  that  it  is  more  just  to  con- 
sider the  Cornish  assay  as  a  metallurgy  on  a  small  scale  than 
as  a  scientific  laboratory  method.  From  thence  result  also 
the  necessity  of  long  practice  and  the  almost  uselessness  of 
theoretical  knowledge  for  those  who  purpose  employing 
this  method  alone. 

Sir  Henry  de  la  Beche  ('  Eeport  on  the  Geology  of 
Cornwall,'  &c.  p.  595),  in  giving  a  sketch  of  the  method, 
declares  it  to  be  rather  rough  and  uncertain,  and  fails  not 
to  add  at  the  conclusion  a  translation  of  a  passage  relative 
to  the  assay  of  copper  pyrites  from  M.  Berthier's  treatise 
on  assays  by  the  dry  way. 

These  drawbacks  upon  the  scientific  value  of  the  Cornish 
method  cannot  injure  the  power  of  facts  ;  they  constitute 
but  another  reason  which  we  may  have  for  giving  an  ac- 
count of  the  manner  in  which  the  first  basis  of  the  valua- 
tion of  the  greater  part  of  the  copper  minerals  has  been 
fixed  since  so  long  a  period. 

Division    Adopted. — The    rather   complex    operations 


ENGLISH   COPPER   ASSAY.  .       383 

through  which  we  have  to  pass  will  be  better  apprehended 
by  explaining  in  succession — 

1.  The  order  of  the  operations,  the  nature  and  influence 
of  the  fluxes  employed,  the  kind   of  products  obtained 
(reactions). 

2.  The  manipulations  to  which  each  operation  gives 
rise,  the  furnaces  and  apparatus  used,  the  characters  of  the 
principal  products  during  the  chief  phases  and  at  the  end 
of  each  (manipulations). 

We  shall  add  to  these — 

3.  Some  information  upon  the  influence  of  the  princi- 
pal foreign  metals  (tin,  antimony,  zinc,  lead),  and  upon  the 
treatment  of  some  special  coppery  matters. 

4.  Summary  considerations  on  the  result  of  the  English 
method  compared  with  those  of  the  analysis  by  the  wet 
way. 

SECTION  I. — KEACTIONS. 

At  the  very  outset  we  distinguish  two  kinds  of  assays. 

1.  The  roasted  sample. 

2.  The  raw  sample. 

The  first  only  applies  to  cupreous  pyrites  or  to  sam- 
ples essentially  formed  of  it — that  is  to  say,  which  contain 
sulphur  in  excess  ;  the  process  begins  by  a  roasting. 

In  the  raw  assay  we  dispense  with  the  roasting  ;  we 
have  recourse  to  the  addition  of  reagents,  either  oxidising 
or  sulphurising,  according  to  the  minerals  ;  we  endeavour 
to  place  them  by  these  mixtures  in  the  condition  of  a  pro- 
perly roasted  pyritic  mineral. 

From  this  point,  at  least  in  general,  the  operations 
become  identical.  They  consist  in — 

1.  Fusion  for  regulus  (regulus). 

2.  Calcining  the  regulus  (calcining). 

3.  Fusing  for  coarse  copper  (coarse  copper). 

4.  One  or  two  fusions  with  fluxes  (washings). 

5.  Trial  by  striking  with  a  hammer,  last  refining  (test- 
ing, refining). 

6.  Treatment  of  slags  for  prilL 


384  ENGLISH    COPPER   ASSAY. 

All  the  slags  except  those  of  the  fusion  for  regulus  have 
been  preserved.  The  fusion  No.  6  gives  a  small  sup- 
plementary button  of  copper,  which  again  undergoes,  if 
necessary,  one  or  two  washings. 

As  we  have  said,  the  roasting  is  used  only  for  pyrites. 
We  shall  return  later  on  to  the  duration  and  the  circum- 
stances of  this  operation.  Its  evident  aim  is  to  drive  off 
the  excess  of  sulphur,  so  as  to  cause  the  whole  of  the  cop- 
per, with  a  part  only  of  the  iron  which  abounds  in  the 
pyrites,  to  pass  into  the  state  of  sulphide  at  the  time  of  the 
fusion  for  regulus. 

I.  Regulus. 

1.  Pyrites. — The  fusion  for  regulus  of  a  properly 
roasted  pyrites  is  made  by  mixing  with  it  equal  volumes 
of  the  three  fluxes — borax,  fluor-spar  in  powder,  lime 
slaked  in  powder — of  each  one  ladle,  and  covering  the 
mixture  with  a  layer  of  moist  common  salt.  The  matters 
composing  the  gangue  of  the  roasted  mineral  consist  prin- 
cipally of  quartz,  silica,  and  in  general  of  more  alumina 
and  magnesia  than  lime ;  oxide  of  iron,  resulting  from  the 
roasting  of  the  pyrites,  is  also  present. 

The  borax  only  serves  to  give  fusibility,  the  fluor-spar 
contributes  to  the  same  end  by  forming  a  fluosilicate. 
Otherwise  it  does  not  play  an  important  part  in  the  de- 
composition— that  is  to  say,  there  is  probably  no  produc- 
tion of  fluoride  of  silicon  and  calcium  ;  for  this  last  base  is- 
added  here  in  considerable  proportion,  so  as  to  form  im- 
mediately a  silicate  which  may  combine  with  the  fluoride 
of  calcium. 

The  ferric  oxide  being  so  reduced  as  to  pass  into  the 
slag,  and  the  different  metallic  oxides  to  pass  into  the  re- 
gulus, yield  oxygen,  which  reacts  on  the  remaining  sulphur. 
The  disengagement  of  sulphurous  acid  which  results  from 
this,  joined  to  the  water  contained  in  the  fluxes,  justifies, 
to  a  certain  extent,  the  use  of  a  layer  of  common  salt, 
designed  to  prevent  the  boiling  over.  Besides  this,  the 
common  salt  being  without  action  on  the  metallic  sul- 


ENGLISH    COPPER   ASSAY.  885 

phides,  does  not    here  produce   those  important   effects 
which  it  exerts  in  the  later  fusions. 

If  the  pyrites  appear  insufficiently  roasted,  we  must  add 
a  little  nitre,  the  oxidising  action  of  which  again  gives 
off  sulphur ;  the  opposite  case,  that  of  a  roasting  too 
much  prolonged,  is  rare ;  we  remedy  it  by  the  addition  of 
sulphur  and  tartar. 

2.  Very  poor  Pyrites. — In  a  very  poor  pyrites — that 
of  Bear  Haven,  in  Ireland,  for  example — the  proportion  of 
sulphur  does  not  require  us  to  have  recourse  to  the  roast- 
ing ;  we  employ  the  three  fluxes  and  one  ladle  of  nitre. 

3.  Variegated  Copper  Ore. — Peacock  ore  contains  less 
sulphur  in  proportion  to  the  copper  than  pyrites ;  we  also 
fuse  with  a  little  nitre. 

4.  Sulphide  of  Copper. — The  sulphur  is  here  insuffi- 
cient.    We  add  together  sulphur  i  to  1  ladle,  according 
to  the  valuation ;  tartar  ^  to  ^  ladle — that  is  to  say,  half 
the  volume  of  the  sulphur.     The  tartar  is  a  powerful  re- 
ducing agent,  and  is  supposed  in  small  quantities  to  favour 
the  action  of  the  sulphur  by  preventing  its  disengage- 
ment as  sulphurous  acid  by  the  oxidising  matters  in  the 
mineral ;  but  if  used  in  excess,  it  acts  as  a  desulphuriser, 
as  well  by  its  carbon  as  by  its  alkali. 

5.  Carbonated  Minerals. — The  addition  of  sulphur  and 
carbon  is  evidently  still  more  necessary  here. 

6.  Native  Mixture  :  f  sulphide  copper,  ^  pyrites. — We 
add,  in  this  case,  nitre  for  the  pyrites,  and  sulphur  and 
tartar  for  the  sulphide  of  copper  ;  although  these  reagents 
appear  sure  to  neutralise  each  other,  it  is  possible  that  their 
simultaneous  employment  may  be  logical.     The  nitre  pro- 
bably decomposes  the  pyrites,  which  would,  without  it,  fuse 
and  give  a  very  ferrous  regulus,  whilst  the  free  sulphur 
would  be  of  little  use,  on  account  of  the  sulphide  of  copper. 
Be  this  as  it  may,  this  is  the  plan  adopted. 

During  the  progress  of  the  fusion  for  regulus  we  have 
still  to  introduce  other  matters,  some  incidentally,  and 
others  in  all  cases. 

If  a  blue  flame  persists  in  escaping  from  the  crucible, 
an  index  of  the  formation  of  sulphurous  acid,  we  project 

c  c 


386  ENGLISH   COPPER   ASSAY. 

into  it  sulphur  1  ladle,  tartar  \  a  ladle.  When  the  fusion 
appears  almost  finished,  in  order  to  render  the  bath  more 
liquid,  and  to  facilitate  the  collection  of  the  button,  we 
throw  in  a  little  dried  salt,  and  a  flux  composed  before- 
hand of  lime,  a  little  fluor-spar,  and  a  very  little  borax — 
that  is  to  say,  of  the  elements  in  different  proportions  of 
the  mixture  introduced  originally. 

The  regulus  obtained  is  composed  principally  of  copper, 
iron,  and  sulphur.  We  shall  return  to  the  aspect  and  the 
richness  which  it  ought  to  have  according  to  the  minerals 
treated. 

II.  Calcining. 

The  calcination  of  the  regulus  is  one  of  the  most  im- 
portant operations ;  it  ought  to  be  quite  complete. - 

-  /  r  •'••'.  ^'-.    :"* 

III.  Coarse  Copper. 

To  the  calcined  regulus  is  added — nitre  J  ladle,  borax 
-|  ladle,  charcoal  -|-  ladle,  dry  salt  I  ladle  (these  quantities 
remain  the  same,  whatever  mineral  may  be  assayed) ;  tartar 
•2  ladles  for  a  regulus  of  medium  richness.  Covering  of 
moist  salt,  2  ladles. 

The  nitre  is  designed  to  burn  the  sulphur  which  may 
have  escaped  the  calcining,  and  to  ensure  the  passage  of 
the  easily  oxidisable  metals,  especially  of  iron,  into  the 
slag  in  the  state  of  oxides.  It  is  besides  in  too  small  pro- 
portion to  act  upon  the  copper,  especially  in  presence  of 
reducers  whose  effect  is  certainly  later  than  the  deflagra- 
tion of  the  nitre. 

The  borax  plays  simply  the  part  of  a  flux. 

The  dry  salt  has  for  its  object  to  give  fluidity  to  the 
slag.  Unfortunately,  if  the  addition  of  the  salt  attains  this 
object,  it  also  determines  from  this  operation  a  sensible 
loss  of  copper  by  carrying  it  away  with  the  saline  vapours. 
We  shall  insist  upon  this  point  in  describing  the  washing. 

The  charcoal  and  the  tartar  are  especially  the  important 
reagents  in  the  fusion.  The  tartar,  at  the  same  time  that 
it  is  one  of  the  most  energetic  reducers,  is  also  a  flux  and 


ENGLISH   COPPER  ASSAY.  887 

a  desulpliuriser.  Its  use  is,  then,  perfectly  justified  here, 
only  the  proportion  of  tartar  added  ought  to  be  regulated 
according  to  the  quantity  of  copper,  which  the  weight  and 
aspect  of  the  regulus  permit  the  experienced  assayer  to 
estimate  sufficiently  closely ;  an  excess  of  tartar  would  re- 
duce the  foreign  metals,  and  produce  in  consequence  a 
very  impure  coarse  copper. 

When  the  fusion  appears  complete,  we  throw  in  some 
white  flux,*  which  gives  fluidity  to  the  slag,  and  deter- 
mines by  its  partial  decomposition,  from  which  a  disen- 
gagement of  carbonic  oxide  results,  a  stirring  up  of  the 
materials.  These  two  effects  facilitate  the  collection  of 
the  metallic  button.  The  potassium  carbonate  begins  also 
without  doubt  from  this  operation  to  refine  the  metal  a 
little  by  attacking  the  iron,  zinc,  and  tin  already  reduced. 
M.  Berthier  (<  Essai  par  la  Voie  Seche,'  vol.  i.  p.  393) 
points  out  this  reaction: — 'A  part  of  the  carbonic  acid 
which  it  contains  being  decomposed  and  changed  into  car- 
bonic oxide,  a  compound  is  formed  consisting  of  alkali, 
carbonic  acid,  and  metallic  oxide,  &c.' 

Lead,  copper,  and  antimony  are  not  attacked. 

IY.   Washings. 

In  the  operation  of  washing  we  put  into  the  crucible, 
at  the  same  time  as  the  coarse  copper,  the  following 
fluxes  : — White  flux,  1  ladle  ;  dry  salt,  2  ladles. 

It  is  evident  that  the  white  flux  is  here  employed  as 
an  oxidiser  of  the  foreign  metals,  and  with  a  view  to  the 
application  of  the  above-mentioned  reaction. 

As  for  the  salt,  it  is  both  useful  and  injurious.  If  it  were 
only  used  with  the  view  of  augmenting  the  fluid  mass  so  as 
to  preserve  the  metal  from  contact  of  air,  &c.,  it  would  be 
advantageously  replaced  by  an  excess  of  white  flux  ;  but  it 
can  form  volatile  chlorides  with  the  arsenic  and  antimony 

*  This  white  flux  is  prepared  in  the  laboratory  by  mixing  in  a  mortar, 
tartar  3  volumes,  nitre  2  volumes,  salt  a  little,  then  determining  the  combus- 
tion by  the  introduction  of  a  red-hot  iron  rod,  which  is  turned  round  until  the 
matter  ceases  to  deflagrate. 

c  c  2 


388  EXGUSH    COPPER   ASSAY. 

which  the  copper  has  retained  in  the  form  of  arsenide 
and  antimonide.  Common  salt  is,  then,  to  be  regarded  as 
one  of  the  principal  agents  of  purification  put  in  operation 
by  the  Cornish  method.  On  the  other  hand,  the  loss  of 
•copper  which  arises  from  the  carrying  off  of  this  metal  by 
the  vapours  of  common  salt  cannot  be  doubted.  M.  Ber- 
thier  has  found  that  by  heating  equal  weights  of  copper 
and  salt  until  the  complete  volatilisation  of  the  latter,  3 
per  cent,  of  the  metal  is  carried  off. 

In  the  event  of  the  coarse  copper  appearing  too  im- 
pure, we  take  care  to  add  a  little  nitre.  According  to  the 
appearance  of  the  button  we  recommend  the  washing  or  not. 

Y.  Testing,  Refining. 

The  button  of  metal  is  flattened  on  an  anvil.  We 
thus  recognise  tin  by  the  hardness,  and  antimony  by  the 
brittleness  of  the  alloy.  The  button  is  then  put  alone  in 
the  crucible.  When  it  presents  a  proper  appearance — 
that  is,  when  the  edges  assume  a  bright  colour,  the  centre, 
which  the  assayer  calls  the  eye,  being  dark — we  hasten  to 
put  into  the  crucible  the  fluxes,  which  are  the  same  as 
for  washing,  only  taken  in  rather  smaller  quantity. 

In  general,  when  we  have  operated  well,  the  button 
obtained  is  of  a  fine  colour,  and  is  regarded  as  pure  ;  if  we 
have  passed  the  eye,  it  is  covered  with  a  layer  of  red 
oxide  ;  if,  on  the  contrary,  we  have  put  in  the  fluxes  too 
soon,  the  button  is  dull. 

It  is  easy  to  give  an  account  of  the  reactions  which 
take  place  during  the  refining,  and  which  differ  a  little 
from  those  of  the  washing. 

In  heating  the  button  alone  in  the  air  in  the  crucible, 
it  is  intended  to  submit  it  to  an  oxidation  which  ought  to 
act  sufficiently  on  all  the  foreign  metals  more  oxidisable 
than  copper  without  acting  too  much  on  the  latter.  The 
proper  point  is  indicated  by  the  appearance  of  the  eye ; 
the  projection  of  the  fluxes  puts  an  end  to  the  atmospheric 
oxidation,  and  determines  the  scorification  of  the  oxides 
which  expel  part  of  the  carbonic  acid  of  the  potassium 


ENGLISH    COPPER   ASSAY.  389 

carbonate,  for  which  they  substitute  themselves,  and  give 
rise  to  triple  compounds  of  metallic  oxides,  alkali,  and 
carbonic  acid. 

The  lead,  tin,  iron,  and  zinc  oxides  behave  thus. 
When  we  have  passed  the  eye,  there  has  been  a  con- 
siderable formation  of  oxide,  which  leaves  the  button 
reddened,  as  I  have  indicated.  At  the  same  time  the  slag 
is  strongly  coloured  red  or  green.  If,  on  the  contrary, 
the  fluxes  have  been  thrown  in  too  soon,  the  oxidation 
has  been  insufficient,  and  then  the  refiner  just  falls  back 
upon  the  preceding  operation  of  washing — an  operation  less 
efficacious  and  even  without  result  in  the  case  of  lead  and 
antimony. 

As  for  the  physical  phenomenon  of  the  eye,  perhaps  it 
corresponds  to  the  very  short  instant  when  the  oxides,  less 
dense  than  the  copper,  are  concentrated  at  the  top  of  the 
button,  and  there  make  a  dark  spot  before  attaining  a 
temperature  sufficiently  elevated  to  acquire  the  brightness 
of  the  metal  itself. 

We  may  add  that  the  minerals  of  Cornwall,  generally 
more  impure  than  foreign  minerals,  require  a  notably 
longer  time  for  the  appearance  of  the  eye. 

Extra  Accidental  Washing. — More  often  the  refining 
gives  a  definite  product,  put  aside  to  be  weighed  with  the 
prill  extracted  from  the  slag  ;  let  the  button  be  clear,  burnt, 
or  dull.  Even  if  the  metal  appeared  too  impure  we  would 
not  recommence  the  refining,  but  would  have  recourse  to 
an  extra  washing  by  putting  at  once  into  the  usual  crucible 
besides  the  button  and  the  usual  fluxes,  the  slag  from  the 
refining. 


- 


VI.  Slags  for  Prill 

All  the  slag  from  the  fusion  for  coarse  copper  in- 
clusively having  been  preserved,  we  fuse  them  all  together 
with : — 

Tartar       .         .         .         1  ladle  I      Simple  reducing 
Charcoal  .        -.        -.        traces    (  mixture 

•   .'  "'  •<-*/    '"  -   •    .-    -~  r;\j    *T     i      ""      i 

We  obtain  a  small  globule  variable  with  the  eircum- 


£90  ENGLISH    COPPER   ASSAY. 

stances  of  the  different  operations  which  have  allowed 
more  or  less  copper  to  pass  into  the  slag.  If  the  prill  is 
not  very  small,  and  its  appearance  indicates  a  metal  not 
sufficiently  pure,  we  submit  it  to  one  or  two  washings,  as 
above. 

SECT.  II. — MANIPULATIONS. 

The  sample,  which  has  been  taken  with  the  utmost 
care,  arrives  at  the  laboratory  rather  coarsely  powdered, 
still  wet,  and  wrapped  in  strong  packing  paper  :  the  paper 
is  opened  and  placed  near  a  furnace  on  the  cast-iron  plate 
which  covers  it ;  the  drying  is  rapidly  done  there. 

The  first  question  is  to  discover  the  kind  or  kinds  of 
minerals,  so  as  to  employ  the  warm  or  raw  sample. 

For  this  purpose  we  throw  one  or  two  large  pinches  of 
the  mineral  into  a  flat-bottomed  copper  dish,  and  we  wash 
it  very  easily  by  putting  in  water  several  times  and  giving 
a  rotatory  motion  to  the  matters,  at  the  same  time  that 
we  incline  the  dish  so  as  to  cause  the  muddy  parts  to  run 
from  the  gangue.  The  small  metallic  fragment  remains 
distinctly  visible,  and  we  can  often  discern  by  simple  in- 
spection the  presence  of  foreign  metals. 

We  weigh  400  grs.  of  the  dried  mineral,  a  quantity 
upon  which  the  assay  is  made. 

The  crucibles  used  in  Cornwall  are  of  three  sizes  : — • 

1.  Large. 

2.  Large  second, 

3.  Small  second. 

The  small  seconds  have  externally  the  internal  dimen- 
sions of  the  large,  into  which  they  fit  as  into  a  nest ;  the 
first  and  third  are  sold  the  one  in  the  other,  and  called 
nested.  They  are  the  most  used. 

The  large  serve  for  the  roasting  and  the  fusion  for 
regulus,  the  small  second  for  calcining  the  regulus  and  all 
the  fusions  which  follow. 

The  large  seconds  are  only  employed  in  place  of  the 
former  when  we  have  to  treat  a  very  large  regulus. 

The  crucibles  are  of  a  kind  rather  wrinkled,  and  as  if 


ENGLISH   COPPER   ASSAY,  391 

fused  superficially  ;  they  present  the  appearance  of  coarse 
stoneware  pottery.  Their  form,  moderately  wide,  permits 
us  to  make  use  of  them  successively  for  the  roasting  and 
the  fusion  for  regulus,  and  gives  them  sufficiently  great 
stability  in  the  fire  of  a  wind-furnace.  They  are  besides 
very  resisting.  They  are  made  at  Truro  and  Redruth. 
The  wind-furnace  has  for  its  principal  dimensions — 


Length  from  front  to  flue 
Breadth        ... 
l)epth  to  the  bars 

Opening  of  the  flue 


«. 


8 
14 

8 
2 

A  sufficiently  large  space  is  reserved  underneath  the 
fire,  where  the  ashes  accumulate  without  inconvenience, 
but  opening  only  by  a  framework  contracted  so  as  not  to 
allow  too  free  an  access  of  cold  air. 

The  furnace  serves  either  for  roastings  or  for  fusions  ; 
in  the  latter  case  we  cover  it  with  two  mounted  bricks,  very 
easy  to  manage,  and  allowing  to  only  half  open  it  when  we 
wish  to  inspect  the  contents  of  the  crucibles.  We  can  con- 
duct ten  roastings  at  once  ;  the  crucibles  are  marked  by 
a  brush  with  colcothar  mixed  with  water.  The  furnace 
having  been  recharged  with  coke,  we  put  the  crucibles  on 
the  top,  and  after  a  few  minutes,  the  substances  beginning 
to  get  warm,  we  stir  them  by  means  of  iron  rods.  Each 
crucible  receives  a  rod,  which  we  leave  standing  there 
(leaning  against  the  chimney)  during  the  whole  period  of 
the  roasting,  so  as  to  avoid  the  loss  which  would  take 
place  if  we  withdrew  the  rod.  From  time  to  time  we 
renew  the  surfaces  by  lightly  taking  hold  of  the  rod  with 
the  left  hand  by  the  upper  end,  whilst  the  right  forefinger 
and  thumb  make  it  turn  at  once  upon  itself  and  round  the 
crucible. 

The  duration  of  the  roasting  varies  essentially  with  the 
nature  and  the  richness  of  the  mineral ;  it  is  never  less 
than  six  or  seven  minutes,  and  may  reach  half  an  hour. 
When  from  the  sandy  appearance  of  the  matters  we  con- 
sider the  operation  finished,  we  withdraw  the  crucible, 


392  ENGLISH    COPPER    ASSAY. 

raise  the  iron  rod  with  care,  and  expose  the  crucible  to  the 
air,  allowing  its  contents  to  cool  slowly.  The  roasting  has 
succeeded  when  the  surface  has  the  brown-red  colour  of 
iron  oxide  and  the  bottom  only  is  black.  In  this  case  we 
proceed  to  the  fusion  for  regulus  by  simply  adding  the 
three  fluxes  (borax^  fluor-spar,  and  lime) ;  if  the  bottom 
of  the  crucible  appear  too  black,  we  ought  to  complete 
the  oxidising  action  by  the  addition  of  a  little  nitre. 


'.       .'     fusion  for  Regulus. 

-  The  different  substances  above  indicated  are  taken 
from  the  box  with  a  slightly  concave  ladle  of  1§  diameter, 
then  mixed  in  the  crucible  with  a  stirring-knife.  We 
ought  to  allow  the  heat  of  the  wind-furnace  to  fall  and 
then  to  recharge,  so  as  to  have  a  gentle  fire  at  the  com- 
mencement of  the  fusion  for  regulus.  The  crucibles  are 
placed  upon  the  coke,  and  supported  against  the  walls  of 
the  furnace,  which  we  then  close  with  the  two  bricks. 
After  about  a  quarter  of  an  hour,  we  open  the  front  brick, 
so  as  to  observe  the  progress  of  the  operation  ;  it  is  at  this 
stage  that  we  throw  the  sulphur  and  tartar  into  those 
crucibles  from  which  a  blue  flame  is  disengaged.  Some 
minutes  later: — that  is  to  say,  nearly  seventeen  minutes 
from  the  commencement — we  adjl  the  salt  and  the  flux 
destined  to  collect  the  regulus  ;  then  (twenty  minutes  from 
the  beginning)  we  run  into  a  metal  mould,  not  greased. 

We  make,  in  general,  several  fusions  at  once — -four, 
for  example  ;  we  have  in  consequence  two  moulds  into 
which  we  pour  the  contents  of  the  crucibles  in  an  adopted 
order,  so  as  to  avoid  all  confusion.  The  matters,  very 
rapidly  solidified,  are  detached  simply  by  a  blow,  and  fall 
in  order  on  a  metal  plate  fixed  in  front  of  the  laboratory 
window.  We  immediately  seize  them  with  the  copper 
tongs,  put  them  into  a  basin  of  the  same  metal,  and  im- 
merse them  for  a  moment  in  cold  water,  where  it  is 
important  not  to  leave  them  too  long.  This  immersion 
allows  us  then"  to  separate  very  easily  the  slag  from  the 


ENGLISH    COPPER   ASSAY.  393 

button  of  regulus,  itself  very  brittle.  For  this  purpose  the 
mass  is  put  on  the  metal  plate,  and  by  means  of  a  hammer 
we  strike  with  care  all  round  the  slag,  which  breaks  off 
pretty  cleanly.  We  hasten  to  detach  from  the  surface  of 
the  regulus  the  slag  which  may  remain  adherent,  using  a 
small  hand  chisel,  without  the  hammer.  The  slags  are 
broken,  and  if  we  find  any  prills  of  regulus  they  are  added 
to  the  principal  button.  Sometimes  in  these  breakings, 
and  especially  in  those  analogous  for  the  last  fusions,  we 
surround  the  substances  by  an  iron  ring,  placed  on  the 
metal  plate,  so  as  to  avoid  loss  of  splinters.  In  a  general 
way,  the  slags  of  the  fusion  for  regulus  are  rejected.  We 
shall  see  further  on  how  it  may  become  necessary  to  flux 
them  again  when  the  mineral  contains  blende. 

The  aspect  of  the  regulus  is  characteristic,  and  it  is 
easy  to  arrive  at  a  pretty  close  estimation  of  its  richness, 
and  consequently  of  the  degree  of  success  of  the  operation, 
by  simple  inspection  of  the  regulus. 

No.  1.  A  very  poor  regulus  (coarse),  that  is  to  say,  too 
much  charged  with  iron,  is  bronzed  and  dull ;  the  opera- 
tion following  would  not  be  able  to  carry  off  the  excess 
of  iron  at  least  without  a  corresponding  loss  of  copper.  A 
like  regulus  evidently  results  from  an  imperfect  warming, 
or  from  an  excess  of  sulphur,  or  from  an  insufficiency  of 
nitre,  as  the  case  may  be. 

It  contains  less  than  40  per  cent,  of  copper.  There  is 
nothing  for  it  but  to  reject  it. 

No.  2.  A  regulus  of  good  appearance  is  in  general 
bronzed  but  rather  shining  ;  it  appears  finer.  Its  richness 
varies  from  40  to  60  per  cent. 

No.  3.  From  oxides,  carbonates,  and  from  some  mine- 
rals charged  with  impurities  (Sn,  Sb)  we  desire  to  obtain  a 
fine  bluish  button  of  a  greater  richness— 65  to  75  per 
cent.  We  perceive,  indeed,  that  from  oxides  and  carbo- 
nates, to  which  we  have  only  to  add  -sulphur,  and  which 
also  by  their  nature  do  not,  like  pyrites,  contain  combined 
iron,  it  is  easy  to  obtain  a  richer  regulus  without  fearing 
any  loss  of  copper.  As  for  the  stanniferous  and  antimonial 
minerals,  we  shall  return  to  them  further  on. 


394 


ENGLISH   COPPER   ASSAY. 


No.  4.  In  every  case  a  regulus,  the  richness  of  which 
rises  to  80  per  cent.,  and  of  a  very  shining  grey- blue  ap- 
pearance, ought  to  be  rejected,  its  richness  indicating  the 
loss  of  a  certain  quantity  of  copper  left  in  the  slag. 

Here  is,  in  the  preceding  order,  the  result  of  the  ana- 
lyses of  four  buttons  whose  description  agrees  with  that 
which  we  have  just  given,  excepting,  perhaps,  No.  2, 
whose  fracture  is  rather  reddish.: — 


Balance  ; 

sulphur 

No. 

Copper 

Iron 

and  traces 

of  foreign 

metals 

1 

Coarse,  to  be  rejected 

36-00 

32-90 

31-10 

2 
3 

Good  in  general  (rather  too  fine) 
Good  for  a  carbonate,  &c.   . 

60-00 
65-60 

1470 
10-50 

25-30 
13-90 

4 

Too  fine,  to  be  rejected 

80-16 

2-10 

17-74 

If  we  compare  these  products  with  those  obtained  in 
the  metallurgy  of  copper  by  the  Welsh  method,  we  find 
(Le  Play,  6  Annales  des  Mines ')  : — 


Matts  of  the  operations. 
II.  V.  IV.  VIII. 

I 

i 

JM 

I! 

I 
1 

16 

|s 

I  Coarse  matt  (fusion  of  poor  mine-1 

II.  -1      rals,  raw  or  calcined) 
1  3Cu,S  +  Fe2Ss  -r  4(Fe  dif.  met)S  ) 

34-6 

34-1 

1-5 

29-8 

31-3 

|Blue  matt  (fusion   of  the  cal-j 

1     cined      coarse     matt      with  L 

57-2 

18-5 

1-0 

23-3 

24-3 

minerals   of   mean   richness) 

^•0'8Cu  +  3CuJ3  +  2(Fe.  d.m.)S 

(Reddish   variety,   matte    mince\ 

61-6 

15-8 

0-6 

22-0 

22-6 

^  \  1  '3Cu  +  3Cu2S  -f  2(Fe.  d.m.  )S     ) 

White  matt  (fusion  of  the  calcined 

coarse  matt  with  rich  minerals, 

r/7    £ 

carbonates,  and  oxides) 

IV. 

Metal  —  very  pure  type     ,.  ,  :     ^ 
very  blue  variety     .  "    *.  ' 

77-4 
64-8 

0-7 
9-0 

0-9 
3-6 

21-0 
22-6 

21-9 
26-2 

mean      .       ,       »  ^.  ^ 

73*2 

6-3 

— 

20-5 

— 

. 

8Cu,S  +  FeS 

VIII. 

Matt    (roasting    of   extra  white) 
matt  VH.) 

81-1 

0-2 

— 

18-5 

— 

ENGLISH    COPPER   ASSAY.  395 

These  numbers  show  the  evident  analogy,  the  identity 
almost,  of  the  products  of  the  laboratory  and  those  of  the 
works  ;  we  may  sum  up  by  saying  that  the  regulus  ought 
to  be  richer  than  coarse  metal,  and  in  the  case  of  ordinary 
minerals  to  approach  if  not  to  attain  (as  in  the  case  of 
sample  No.  2)  to  the  composition  of  blue  metal. 

For  carbonated  and  oxidised  minerals  we  arrive 
directly  at  the  very  bluish  variety  of  white  metal. 

Finally,  in  no  case  must  we  have  a  button  as  rich  as 
regulus  matt. 

Calcining  the  Matt. 

The  matt  is  pounded  fine  in  a  bronze  mortar  ;  we  avoid 
loss  of  fragments  by  means  of  a  perforated  cover  and  a 
cloth  which  surrounds  the  pestle.  To  facilitate  the  pulve- 
risation, and  avoid  the  sulphide  greasing,  we  add  in  the 
mortar  a  small  piece  of  coke.  The  pounded  matt  is  care- 
fully turned  upon  a  sheet  of  paper,  the  mortar  wiped  out 
with  a  hare's  foot,  and  the  substance  put  into  a  small 
second  or  large-second  crucible.  The  calcining  is  con- 
ducted as  the  roasting  of  a  mineral ;  it  generally  lasts 
longer,  for  the  expulsion  of  the  sulphur  is  to  be  as  com- 
plete as  possible.  It  is  necessary  to  regulate  the  fire  with 
the  greatest  care,  so  as  to  avoid  all  agglomeration,  and  to 
stir  almost  continually.  When  the  matter  adheres  to  the 
rod,  we  withdraw  the  crucible  for  a  moment ;  this  incon- 
venience is  chiefly  produced,  if  we  have  not  detached 
the  slags  sufficiently  from  the  matt ;  the  calcining  is  then 
much  longer,  the  flames  remain  blue  a  long  time,  and  the 
fumes  which  are  disengaged  have  an  odour  which  is  not 
purely  that  of  sulphurous  acid.  When  the  fumes  and  the 
odour  cease,  and  the  matter  has  taken  a  sandy  appearance* 
we  raise  the  heat ;  then  withdraw  the  crucible,  and  allow 
it  to  cool  slowly  in  the  air  as  when  roasting. 

The  mean  duration  of  calcining  is  half  an  hour. 


396  ENGLISH    COPPER   ASSAY. 


Coarse  Copper. 

The  fluxes  above  indicated  are  taken  from  a  box  No.  1, 
except  the  dry  salt  called  the  refining  flux,  which  forms 
part  of  a  second  box.  The  ladle  for  this  box  No.  2  is  a 
little  larger  than  for  the  first;  it  has  a  diameter  of  1^ 
inch.  At  the  beginning  of  the  operation  the  furnace  is 
well  filled  and  lighted  ;  the  same  fire  ought  to  suffice  for 
all  the  following  fusions,  which  it  is  very  important  to 
conduct  with  great  rapidity.  After  a  moment,  and  if  there 
is  any  frothing,  we  throw  in  some  dry  salt,  which  calms 
the  ebullition.  At  the  end  of  ten  minutes,  the  fusion  ap- 
pearing complete,  we  throw  in  a  pinch  of  white  flux.  A 
little  after  we  withdraw  successively  each  of  the  crucibles, 
pouring  them  carefully  and  by  a  single  turn  into  each  of 
the  principal  cavities  of  the  metal  mould.  These  moulds 
ought,  this  time  only,  to  be  greased  with  a  cloth  impreg- 
nated with  suet.  The  crucibles  are  immediately  put  back 
again  into  the  fire. 

We  detach  the  slag  as  previously,  seize  each  one 
successively  with  the  copper  tongs,  and  plunge  it  for  an 
instant  into  a  basin  full  of  water.  The  rest  is  effected  as 
for  the  regulus,  only  the  slags  are  preserved  on  the  metal 
plate,  and  in  the  order  in  which  we,  have  detached  them. 
The  button  of  copper  obtained  appears  more  or  less  black  ; 
I  have  already  iftdicated  the  influence  of  the  tartar  in 
excess. 

Washings. 

We  place  the  button  and  the  fluxes  in  a  large  copper 
shovel,  lengthened  and  narrowed  at  the  end,  called  a  scoop, 
and  we  pour  them  into  the  crucible,  which  is  already  at  a 
red  heat.  As  the  fusion  is  made  in  five  or  six  minutes,  it 
would  be  inconvenient  to  prolong  it  on  account  of  thejoss 
occasioned  by  the  carrying  off  of  copper  with  the  vapours 
of  common  salt.  The  pouring  is  made  with  care  by  pour- 
ing first  into  one  of  the  large  cavities,  then  as  soon  as  the 


ENGLISH    COPPER  ASSAY,  397 

metal  has  fallen  there  we  finish  by  pouring  the  slag  into 
one  of  the  small  lateral  cavities.  This  last  slag,  probably 
rich  in  copper,  is  less  fluid,  and  would  adhere  to  the  but- 
ton, which  would  be  difficult  to  cleanse.  The  two  buttons 
being  detached  from  the  mould,  we  immerse  the  small  one 
first,  then  finish  as  in  the  preceding  operation. 

Testing  and  Refining. 

The  crucible  has  again  been  put  back  into  the  furnace, 
after  the  pouring  ;  the  button  tried  by  the  hammer  is  put 
into  the  crucible  by  means  of  the  tongs.  At  the  end  of 
about  three  or  four  minutes  it  attains  the  colour  of  the 
vessel,  the  eye  manifests  itself,  and  we  rapidly  throw  in 
the  fluxes  put  into  the  scoop  beforehand. 

The  pouring  is  done  as  for  the  washing,  with  the  small 
button  of  slag  kept  apart. 

In  general  we  get  a  button  regarded  as  pure,  clean 
copper  ;  if  not,  as  I  have  said,  we  proceed  to  an  extra 
washing  by  adding  exceptionally  in  the  scoop  the  last  slag 
obtained. 

Prill. 

The  crucible  this  time  has  been  left  out  of  the  furnace  ; 
put  into  it  all  the  slags,  collected  for  this  purpose  from 
the  metal  plate  into  the  scoop,  and  upon  which  we  have 
put  reducing  reagents.  The  fusion  lasts  a  quarter  of  an 
hour ;  pour  all  at  once  into  the  large  cavity  ;  before  the 
cooling,  by  means  of  a  transverse  blow,  get  rid  of  the 
upper  beds  which  are  still  liquid,  and  composed  principally 
of  common  salt.  Then  operate  as  above.  Collect  the 
prill,  which  again  undergoes,  if  necessary,  a  washing. 

SECT.  III. — SOME  MINERALS  AND  SUBSTANCES  OF  A  SPECIAL 
NATURE — INFLUENCE  OF  FOREIGN  METALS. 

STANNIFEROUS  MINERALS. — Most  often  we  only  perceive 
the  presence  of  tin  in  a  copper  mineral  when  testing  with 
the  hammer,  which  reveals  the  nature  of  the  bronze  ; 


308  ENGLISH    COPPER   ASSAY. 

when  we  proceed  to  the  refining  of  such  a  stanniferous 
button,  it  is  impossible  to  obtain  the  characteristic  eye  ; 
that  is  to  say,  the  surface  of  the  metal  becomes  quite  clear, 
and  we  scarcely  open  the  furnace  when  it  again  becomes 
obscure.  We  free  it  from  tin  by  two  or  three  extra  wash- 
ings. If  we  suspect  tin  from  the  known  produce  of  the 
mineral,  or  the  inspection  of  the  sample  in  the  basin,  we 
endeavour  to  obtain  a  fine  regulus,  which  is  accomplished 
in  the  case  of  a  warm  sample  by  prolonging  the  calcining, 
and  for  the  raw  sample  by  putting  in  more  nitre  or  less 
sulphur.  It  is  clear  that  tin  can  only  enter  the  regulus  by 
virtue  of  the  excess  of  sulphur  necessary  to  the  formation 
of  the  coppery  matt,  and  that  by  restraining  this  excess  of 
sulphur  we  diminish  the  chance  of  tin  entering  the  button. 
The  fine  regulus  ought  to  contain  70  to  75  per  cent,  of 
copper,  as  for  the  carbonated  copper  minerals. 

ANTIMONIAL  MINERALS. — Antimony  is  also  detected  in  the 
testing  ;  the  metal  being  rendered  very  brittle.  We  then 
add  one  or  two  grammes  (15  to  30  grains)  of  lead  in  the 
refining  operation.  There  forms  an  alloy  of  lead  and  an- 
timony heavier  than  copper,  which  is  poured  into  the  small 
cavity  of  the  mould.  When  we  suspect  antimony,  we  act 
as  for  tin — that  is  to  say,  we  produce  a  fine  regulus,  a 
most  careful  roasting  expelling  the  antimony ;  then  we 
have  to  make  two  washings,  and  in  the  second  to  add  the 
metallic  lead. 

We  cause,  then,  three  influences  to  act  with  a  view  ot 
expelling  the  antimony  : — 

1.  Slow  oxidation  at  a  low  temperature,  disengaging 
antimony. 

2.  Eepeated  chloridations,  from  whence  a  formation  of 
volatile  chlorides. 

3.  Affinity  of  the  lead  and  mechanical  separation  of  the 
alloy. 

ZINCIFEROUS  MINERALS. — One  of  the  metals  which  is 
most  troublesome  is  zinc.  We  recognise  it  by  the  appear- 
ance of  the  regulus  and  by  its  colour,  which  is  that  of 
blende.  Once  out  of  ten  the  regulus  collects  sufficiently 
to  be  able  to  detach  it ;  in  this  case  we  pound  it,  add  to 


ENGLISH   COPPER   ASSAY.  399 

it  the  slags,  and  borax  1  ladle,  nitre  \  ladle.  We  fuse 
anew,  and  obtain  a  good  regulus,  for  the  nitre  has  caused 
the  zinc  to  pass  into  the  slag  in  the  state  of  oxide. 

Most  often  the  zinciferous  regulus  does  not  collect,  and 
there  is  nothing  for  it  but  to  begin  anew  by  making  a 
very  prolonged  roasting  of  at  least  half  an  hour. 

PLUMBIFEROUS  MINERALS. — Lead  is  not  injurious,  for  it 
does  not  alloy  with  copper.  The  warming  is  also  pro- 
longed. Lead  passes  into  the  regulus,  which  facilitates  the 
collection  of  the  matter.  In  the  last  operation  the  lead 
easily  passes  into  the  slag  ;  it  also,  in  case  of  need,  carries 
off  antimony.  Thus  the  copper  obtained  from  lead  minerals 
is  most  malleable. 

Special  Cupriferous  Products. 

BEGULUS  OF  CHILI. — These  arc  treated  as  those  which 
we  obtain  by  the  fusion  for  regulus.  Their  richness, 
which  rises  to  nearly  60  per  cent.,  requires  us  to  add 
much  tartar  in  the  fusion  for  coarse  copper. 

SLAGS  OF  COPPER. — To  obtain  regulus  we  add  to  the  slag 
sulphur,  tartar,  and  nitre :  this  last  maintaining  metals 
other  than  copper  in  the  state  of  oxide  in  the  slag. 

OLD  COPPER. — For  turnings,  waste  of  workshops,  &c., 
yielding  97  to  98  per  cent,  by  the  assay,  and  containing, 
in  fact,  not  much  foreign  matter  except  a  li ttle  mixed  dust 
or  dirt,  we  take  care  first  to  glaze  the  crucible  by  fusing 
in  it  a  little  borax  and  nitre  ;  then  we  treat  the  matters  by 
a  simple  washing,  the  slags  of  which  we  work  for  prill. 
This  last  is  often  very  considerable. 

SECT.  IV. — SUMMARY  CONSIDERATIONS — COMPARISON  OF  THE 
EESULTS  WITH  THE  ANALYSIS  BY  THE  WET  WAY. 

After  this  detailed  account  of  the  numerous  operations 
which  the  metal  undergoes  before  attaining  the  state  of 
button  and  prill,  it  would  be  superfluous  to  insist  upon  the 
practical  difficulty  of  the  Cornish  method. 

Nevertheless,  in  experienced  hands,  and  in  the  case  of 


400 


ENGLISH    COPPER   ASSAY. 


daily  practice,  it  is  still  a  rapid  method,  allowing  us  to 
.treat  almost  uniformly  the  different  varieties  of  copper 
mineral,  and  at  the  least  to  remedy  during  the  operation 
itself  the  impurities  which  show  themselves. 

As  to  the  metallurgic  accuracy,  here  is  a  small  table 
showing  comparatively  the  produce  by  the  dry  wTay  (de- 
termined by  a  Cornish  assayer)  and  that  which  we  have 
obtained  by  the  most  precise  methods  of  the  wet  way.  It 
comprehends  six  samples,  whose  richness  varies  within 
sufficiently  great  limits. 


Nature  of  the  sample 

Dry  way 

Wet  way 

Difference 

and  produce 

D. 

W. 

W—  D. 

Regulus  of  Chili    .         .         .         .         . 

56^  =  56-250 

58-40 

2-150 

Green  copper  carbonate  of  Castile 

9f=   9-750 

11-52 

1-770 

Variegated  copper,  Huel  Damsel  . 

10*-=10500 

11-30 

0-800 

Pyrites,  West  Wheal  Seton 

8|=   8-375 

8-40 

0-025 

„       United  Mines  . 

8   =   8-000 

10-38 

2-380 

„       Devon  Great  Consols 

4£=   4-625 

5-60 

0-975 

2(W     D)                         8'10° 

Mean  difference     .             .  —    /»  1'35Q°/ 

find 


By  adding  the  result  given  by  the  last  five  minerals  we 

=  41-25,  5(W-D)  =  5-95,  SW=47'20,  and 
SW 


=  9-44 


By  taking  the  ratio 


we  see  that  we  must  add  to  the  richness  indicated  by  the 
Cornish  assay  about  f  of  that  result,  and  by  taking  the 
ratio 

2(W-D)  =12-60, 


that  the  loss  is  -J-  of  the  copper,  if  we  consider  a  mineral 
of  9  or  10  per  cent* 


ENGLISH    COPPER   ASSAY.  401 

Without  wishing  to  draw  a  conclusion  altogether 
general  from  so  small  a  number  of  analyses,  we  neverthe- 
less think  they  suffice  to  show  that  the  Cornish  method 
occasions  losses  always  sensible  and  sometimes  considerable. 
We  think  we  may  assert  that  upon  the  whole  of  the 
Cornish  minerals  whose  mean  richness  varies  from  6  to  7 
per  cent.,  the  loss  by  the  assay  is  not  less  than  20  per 
cent,  of  the  contained  copper,  and  that  for  certain  pyrites 
of  3  to  4  per  cent,  it  attains  30  and  40  per  cent,  of  the 
metal. 

The  principal  causes  of  these  losses  are — (1st) "The 
quantity  more  or  less  great  of  copper  left  in  the  slag  of 
the  regulus  ;  (2nd)  and  especially  the  carrying  away  of 
copper  by  the  vapours  of  common  salt  in  the  fusion  for 
coarse  copper,  the  washing  or  washings,  the  refining  and 
the  treatment  of  the  slag  for  prill. 

In  consequence  we  think  they  ought  to  bear  princi- 
pally on  the  oxidised  minerals  for  which  we  make  a  rich 
regulus,  and  still  more  on  the  impure  minerals,  which 
besides  a  rich  regulus  have  undergone  several  washings. 
Thus  the  minerals  of  Algeria,  grey  copper,  assayed  some 
years  ago  at  the  School  of  Mines,  have  given  a  produce 
much  higher  than  that  indicated  by  the  Cornish  assayers. 

It  may  be  said  therefore  that  the  results  of  the  Cornish 
assay  do  not  fall  short  of  the  truth  by  a  fixed  quantity* 
but  become  more  and  more  inaccurate  the  poorer  the  ore. 
The  smelter  gets  out  of  the  ore  more  metal  than  the  assay 
indicates. 

The  most  frequent  alloys  of  copper,  i.e.  brass,  German 
silver,  gun-metal,  &c.,  cannot  be  assayed  in  a  reliable 
manner  in  the  dry  way.  German  silver,  because  the 
nickel  could  not  be  removed  at  all,  or  only  with  great 
difficulty,  and  the  rest  because  zinc  and  tin  give  such  diffi- 
cultly fusible  oxides,  that  they  could  not  be  properly 
removed  in  the  refining. 

In  the  alloys  of  copper  with  silver,  gold  and  platinum , 
the  copper  may  be  determined  from  the  loss  arising  from 
cupellation  with  lead. 

In  all  assays  of  copper  in  the  dry  way,  the  silver  or 

D  D 


402  ASSAYS   IN   THE    WET    WAY. 

auriferous  silver  contained  in  the  assay  sample  cannot  be 
removed,  and  it  is  generally  pretty  completely  collected 
in  the  copper  obtained.  These  copper  assays  give  no- 
where any  indications  whether  gold  or  silver  is  present 
or  not ;  and  the  amount  of  these  metals  which  may  be 
present  must  therefore  be  both  sought  for  and  determined 
by  a  special  assay  for  them.  If  they  are  found,  and  in 
sufficiently  large  quantity,  they  are  deducted  from  the 
weight  of  the  copper. 

The  dry  assay  is  mostly  found  in  practice  in  smelting 
works,  where,  even  in  the  hands  of  less  scientifically  edu- 
cated than  skilful  assayers,  with  the  character  of  the  assay 
substance  once  known,  and  suitable  practice  in  following 
out  the  separate  manipulations,  it  gives  results  which 
suffice  for  the  business  of  working  copper  in  the  large 
way. 

B.   ASSAYS   IN   THE  WET   WAY. 
a.    Colorimetric  Copper  Assays. 

These  are  based  upon  the  fact  that  ammonia,  added  in 
excess  to  the  solutions  of  salts  of  copper,  produces  a 
beautiful  azure  blue  colour,  whose  intensity  depends  upon 
the  quantity  of  copper  dissolved.  By  comparing  the 
shades  of  blue  colour  in  equally  thick  layers  of  the  dis- 
solved ammoniacal  assay  substance  (assay  fluid)  with  a 
normal  or  standard  ammoniacal  fluid  whose  copper 
contents  are  known,  the  quantity  of  copper  in  the  former 
can  be  calculated  when  its  volume  is  measured. 

To  Heine,  the  superintendent  of  the  smelting  works  in 
Mansfeld,  belongs  the  merit  of  having  first  successfully 
employed  this  reaction  for  the  determination  of  small  per- 
centages of  copper  ;  and  later  it  has  been  also  extended  by 
Jacquelain,  Von  Hubert,  and  Mliller,  to  the  determination 
of  larger  quantities  of  copper. 


COLOR1METRIC   ASSAYS.  403 


1.  HEINE'S  COLORIMETRIC  METHOD. 

For  the  determination  of  the  quantity  of  copper  in 
bodies  poor  in  this  metal,  e.g.  in  slags,  lead  matt,  litharge, 
crude  lead,  and  other  plumbiferous  metallurgical  pro- 
ducts, tin,  cupelled  silver,  &c.  ;  in  short,  in  all  substances 
which  contain  from  a  trace  to  about  1  per  cent,  or  a  little 
more  of  copper,  this  method  is  the  most  advantageous  to 
be  used. 

After  the  assay  sample  has  been  reduced  to  as  fine  a 
state  of  mechanical  subdivision  as  possible,  which  with 
slags  is  best  attained  by  sifting  or  washing  them,  one 
centner  (3-4  grammes)  of  it  is  weighed  out  and  dissolved, 
or  so  completely  decomposed  by  a  suitable  acid  that  in 
the  residue,  which  is  to  be  filtered  and  well  washed,  no 
more  copper  remains  behind.  For  this  purpose  nitric  acid 
or  aqua  regia  is  employed,  according  to  the  character  and 
particular  behaviour  of  the  substance,  and  the  nitric  acid 
is  concentrated  or  somewhat  diluted,  as  may  be  required. 
The  solution  is  either  immediately,  or  after  the  copper 
has  been  first  precipitated  by  sulphuretted  hydrpgen  gas 
and  again  dissolved,  strongly  supersaturated  with  caustic 
ammonia,  and  the  precipitate,  if  any,  thereby  produced, 
digested  in  caustic  ammonia  for  a  considerable  time,  with 
frequent  stirring  at  a  very  gentle  heat  (30°-40°  C.),  then 
filtered  off  and  thoroughly  washed.  According  to  the 
quantity  of  copper  present,  and  according  to  the  degree 
of  dilution,  the  solution  obtained  will  appear  more  or 
less  strongly  coloured  blue.  The  volume  of  the  solution 
is  measured  in  graduated  vessels,  and  the  intensity  of  the 
colour  compared  with  and  determined  from  fluids,  which 
have  been  previously  prepared  as  standard  fluids,  and 
which  for  a  definite  volume  contain  a  definite,  accurately 
weighed  quantity  of  copper,  that  has  been  dissolved  in 
nitric  acid,  precipitated  by  caustic  ammonia,  and  redis- 
solved  in  excess  of  the  same.  From  the  measured  volume, 
and  the  intensity  found  by  comparison,  the  quantity  of 
copper  is  then  determined  by  calculation. 

D   D   2 


404  THE    ASSAY    OF    COPPER. 

Heine  proposes  standard  fluids  with  one,  two,  three, 
and  four  assay  loth  of  copper  in  one  ounce  (two  lot]], 
commercial  weight)  of  the  ammoniacal  fluid.  These  four 
standard  fluids  are  all-sufficient. 

If  the  French  weights  and  measures  are  used,  standard 
fluids  are  taken  with  -001,  -002,  -003,  -004  grammes  of 
copper  to  every  twenty-five  cubic  centimetres  of  the  fluid. 

The  graduated  vessels  (cylinders)  required  for  the 
preparation  of  the  standard  fluids,  as  well  as  for  the 
measuring  of  the  assay  fluid,  can  be  easily  prepared  by 
the  assayer  himself.  One  quarter  of  an  ounce  of  water  is 
weighed  out  a  number  of  times  in  succession  and  poured 
into  the  cylinder,  and  each  time  the  height  of  the  fluid  is 
marked  in  a  durable  manner  on  the  glass  with  a  diamond, 
or  by  etching  it  with  hydrofluoric  acid  vapour,  &c.  Also 
earthen  or  porcelain  measures,  that  are  prepared  and 
marked  for  the  volumes  that  hold  one,  two,  three,  four, 
&c.,  ounces  of  water,  may  be  used. 

It  is  not  practicable  to  replace  the  volumetric  measure- 
ment by  weighing,  for  the  quality  and  quantity  of  those 
substances  which  are  soluble  in  acids  and  not  precipitated 
by  ammonia,  or  are  again  dissolved  by  it,  may  vary  greatly 
in  the  assay. 

In  the  formation  of  the  normal  fluids,  two  assay  pounds 
of  chemically  pure  (galvanic)  copper  are  weighed  out  on  a 
good  balance,  dissolved  in  nitric  acid,  the  solution  super- 
saturated with  caustic  ammonia,  and  placed  in  a  graduated 
cylinder,  which  is  divided  to  whole,  half,  and  quarter 
ounce  volumes  of  water,  and  then  water  enough  is  added 
to  bring  the  fluid  to  the  sixteen-ounce  mark.  The  fluid 
then  contains  f-f =4  loth  of  copper  per  ounce.  Six  ounces 
of  this  four-loth  solution  are  then  taken,  two  ounces  of 
water  added  to  it,  and  eight  ounces  of  fluid  obtained,  with 
%4  =  3  loth  of  copper  to  one  ounce  of  water.  The  two-loth 
solution  is  formed  in  a  similar  way  by  diluting  four  ounces 
of  the  four-loth  solution  to  eight  ounces  ;  the  one  loth,  by 
diluting  four  ounces  of  the  four-loth  normal  fluid  to  six- 
teen ounces.  In  the  measuring  of  the  assay  fluid  it  is 
estimated  within  one-eighth  of  an  ounce,  which  is  suffi- 


COLORIMETRIC   ASSAYS.  405 

ciently  close.  If  in  the  dilutions  a  mistake  is  actually 
made  of  one-sixteenth  of  an  ounce,  the  maximum  of  possi- 
bility, the  error  amounts  to  about  two  cubic  centimetres, 
which  in  a  whole  mass  of  fluid  of  200-500  cubic  centi- 
metres has  no  influence  upon  the  solution  that  can  be 
detected  with  the  eye. 

The  preservation  of  the  standard  fluids,  as  well  as  the 
comparison  of  the  blue  assay  fluids  with  them,  must  take 
place  in  glass  vessels  closed  with  ground-glass  stoppers. 
These  vessels  must  have  the  same  form  and  size,  consist  of 
the  same  colourless  glass,  and  have  an  equal  thickness  of 
glass  in  the  smooth  side  walls.  The  last  condition  is 
obtained  the  surest  by  grinding.  This  grinding,  however, 
which  notably  increases  the  cost  of  the  glasses,  is  not 
indispensably  necessary  if  the  vessels  are  carefully  formed 
and  blown  in  a  good  glass-house.  An  oblong  form  is  most 
advantageous  for  the  vessels.  They  hold  about  an  ounce 
and  a  half  of  fluid,  and  are  about  two  inches  long,  two  and 
a  half  inches  high,  and  one  inch  wide,  with  walls  about 
one-eighth  of  an  inch  thick. 

The  glasses  are  very  advantageously  formed  from 
an  unblemished  sheet  of  plate  glass  of  equal  thickness 
throughout,  by  cementing  the  sides  together  and  the 
insertion  of  a  glass  neck.  The  assay er  has  in  the  form  of 
vessel  indicated  a  triple  control  in  the  comparison  of  the 
assay  fluid  with  the  normal  solution  according  as  he  looks 
through  the  fluid  in  three  different  directions. 

The  digestion  of  the  assay  sample  with  acid  may  take 
place  in  any  suitable  vessel  whatever,  a  glass  flask,  a 
beaker  covered  with  a  watch-glass,  &c.,  only  no  thumping 
and  spirting  of  the  fluid  should  be  possible  in  the  process. 
The  nitric  acid,  &c.,  must  be  added  little  by  little.  The 
time  required  for  this  may  vary  greatly.  The  solution  of 
cupelled  silver*  skimmings,  &c.,  with  nitric  acid  is  finished 
in  a  short  time  ;  on  the  other  hand,  in  the  examination 
of  difficultly  decomposable  slags,  with  which  concentrated 

*  With  cupelled  silver,  after  dissolving  in  nitric  acid,  the  silver  may  be 
precipitated  with  sodium  chloride,  the  silver  chloride  filtered,  washed,  and  the 
solution  then  mixed  with  caustic  ammonia. 


406  THE    ASSAY   OF   COPPER. 

nitric  acid  or  aqua  regia  will  always  be  used,  the  digestion 
often  requires  to  be  continued  at  a  warm  temperature  for 
two  to  three  times  in  twenty-four  hours.  The  mass  must 
be  frequently  stirred  with  a  glass  rod,  because  many  slags 
decompose  rapidly  with  evolution  of  heat,  form  a  thick 
jelly,  and  deposit  a  crust  on  the  bottom  of  the  glass — sub-,, 
mono-,  and  bi-silicate  slags  mostly  decompose  readily, 
higher  silicates  resist  complete  decomposition  by  aqua 
regia — and  then  a  preliminary  solvent  ignition  or  fusion 
with  potassium  carbonate  or  calcined  sodium  carbonate, 
or  better,  a  mixture  of  both,  is  necessary,  precisely  in  the 
manner  given  in  the  wet  assay  of  copper.  Here  also  it 
does  no  harm  if  some  of  the  substance  of  the  crucible 
remains  adhering  to  it. 

The  decomposition  of  the  slags  by  acid  is  complete 
when  in  the  stirring  with  a  glass  rod  no  more  grating  can 
be  perceived. 

After  hot  water  has  been  added  to  the  decomposed 
assay,  the  residue  is  collected  on  a  filter,  well  washed  out, 
without  diluting  the  filtrate  too  largely,  and  the  copper 
precipitated  from  the  solution,  if  necessary,  with  sulphu- 
retted hydrogen  gas,  especially  when  a  notable  quantity  of 
alumina  and  iron  is  present,  whose  slimy  precipitates  from 
the  immediate  precipitation  with  ammonia  always  retain 
copper.  This  precipitation  of  the  copper  has  also  the 
advantage  that,  as  cobalt  and  nickel  do  not  precipitate 
with  it,  the  colouring  effects  which  they  would  produce, 
if  present,  are  removed.  Since  the  copper  sulphide 
requires  for  its  solution  but  a  few  drops  of  nitric  acid,  in 
the  succeeding  treatment  of  the  solution  with  ammonia, 
but  a  small  quantity  of  ammoniacal  salt  is  formed,  and  the 
specific  gravity  of  the  coloured  fluid  varies  but  very  little 
from  that  of  water  and  the  normal  solution.  With  the 
increase  of  the  specific  gravity  of  the  assay  solution,  its 
volume  is  considerably  increased,  and  therefore  it  gives 
too  large  a  measure  in  the  direct  precipitation  with 
ammonia.  If  the  precipitation  with  sulphuretted  hydrogen 
gas  is  completed  in  four  to  six  hours,  the  copper  sulphide 
is  filtered  out,  thoroughly  washed  with  cold  water  contain- 


COLORIMETRIC   ASSAYS.  407 

ing  sulphuretted  hydrogen,  the  filter  dried,  ignited  in  a 
porcelain  crucible,  the  copper  oxide  formed  warmed 
with  a  few  drops  of  nitric  acid  or  aqua  regia,  supersatur- 
ated with  ammonia,  filtered,  and  well  washed,  till  the 
washings  are  no  longer  tinged  bluish. 

A  precipitation  of  the  copper  with  iron  wire,  from  a 
solution  evaporated  with  sulphuric  acid,  and  a  re-solution 
of  the  copper  in  nitric  acid,  consumes  less  time.  If  the 
copper  is  not  precisely  precipitated,  errors  of  some  30 
per  cent,  and  more,  of  the  whole  amount  of  copper  may 
occur.  By  repeated  solution  of  the  iron  precipitate  and 
precipitation  with  ammonia,  all  the  copper  cannot,  however, 
be  extracted. 

In  the  examination  of  litharge,  the  solution  in  nitric 
acid  may  be  dispensed  with.  The  copper  oxide  can  be  at 
once  extracted  from  it  with  caustic  ammonia ;  however* 
.  the  litharge  and  ammonia  must  then  be  allowed  to  work 
at  least  twenty-four  hours  on  each  other,  with  very  diligent 
stirring,  and,  moreover,  the  litharge  must  be  ground  very 
fine. 

The  ammoniacal  solution  obtained  from  the  assay  is 
now  well  stirred,  so  that  it  may  mix  with  perfect  unifor- 
mity with  the  last  washings  ;  then,  either  the  whole,  or  a 
part  of  it,  is  placed  in  a  clean  assay  glass,  and  compared 
with  the  standard  fluids  in  similarly  formed  glass  vessels 
standing  on  a  sheet  of  white  paper.  Should  it  correspond 
with  none  of  them  in  the  intensity  of  its  colour,  the  whole 
of  the  fluid  is  diluted  somewhat  with  water,  until  this  is  the 
case.  Its  volume  is  thereupon  measured  in  the  glass 
vessel  graduated  to  ounces,  &c.,  and  noted.  For  a  check, 
the  dilution  may  be  carried  still  farther  till  the  colour  of 
the  assay  corresponds  to  the  next  more  faintly  coloured 
standard  fluid,  and  then  the  increased  volume  be  measured 
anew.  This  might  perhaps  be  still  again  repeated,  but  it 
becomes  more  and  more  uncertain.  The  calculation  of 
the  percentage  of  copper,  from  the  intensity  and  the  volume 
found,  then  presents  no  further  difficulty. 

Suppose  that  the  assay  fluid  agrees  with  the  normal 
solution  of  four  loth  of  copper  to  the  ounce  of  water,  and 


408  THE    ASSAY   OF   COPPER. 

its  quantity  amounts  to  five  ounces,  then  the  quantity  of 
copper  in  the  centner  of  the  assay  substance  is  5  x  4  =  20 
loth.  This  fluid  further  diluted  till  it  equals  the  normal 
solution  with  three  loth  of  copper,  must  measure  six  and 
two-third  ounces  if  the  obtained  value  of  twenty  loth  is  to 
be  confirmed. 

According  to  Heine's  experiments,  the  possible  error 
of  observations  in  the  comparisons  and  measurement  de- 
scribed amounts  as  a  maximum  with  the  stronger  normal 
solutions  (with  sixteen  loth  and  over)  to  from  three-quarters 
to  one  loth,  with  the  weaker  ones  to  scarcely  half  a  loth  of 
copper.  In  a  centner  of  the  assay  substance,  one  loth  of 
copper  -03  per  cent,  can  still  be  determined  with  cer- 
tainty. 

Le  Play  determined  in  finely  pulverised  and  carefully 
washed  copper  slags,  the  copper  in  one  gramme  of  the 
poorest  slags  to  within  half  a  milligramme,  and  of  the. 
richest  slags  to  within  one  milligramme,  by  using  twenty- 
six  standard  fluids  with  various  percentages  of  copper  in 
cylindrical  vessels.  The  comparison  of  colours  in  round 
vessels  is  more  uncertain  than  in  oblong  ones,  since  in 
the  former  the  light  is  dissipated  and  shadows  are  pro- 
duced. 

According  to  Mr.  T.  0.  Cloud,  the  copper  cannot  be 
completely  extracted  from  the  finest  ground  slags,  even 
after  three  days'  digestion  with  aqua  regia,  and  subsequent 
treatment  with  sulphuric  acid.  He  recommends  to  fuse 
the  slag  with  four  parts  of  mixed  potassium  and  sodium 
carbonates  and  ^  part  potassium  nitrate.  The  fused  mass 
is  extracted  with  dilute  sulphuric  acid,  the  liquid  evapo- 
rated down,  and  the  copper  determined  galvanically  or 
colorimetically. 

As  a  delicate  test  for  small  quantities  of  copper,  Dr. 
Endemann  ('Annalen  der  Chemie ')  adds  to  the  dilute  solu- 
tion concentrated  hydrobromic  acid,  when  a  dark  brownish- 
red  or  violet  colour  is  at  once  produced. 

This  reaction  is  so  delicate  that  T^  milligramme  of 
copper  can  be  detected  with  certainty.  One  drop  of  a 
solution  containing  this  small  quantity  of  copper  is  brought 


COLOKIMETRIC   ASSAYS.  409 

i 

on  a  watch-glass,  then  one  drop  of  hydrobroniic  acid  is 
added,  and  the  solution  is  then  allowed  to  evaporate  slowly 
by  standing  the  glass  on  a  warm  place.  When  the  whole 
has  been  concentrated  to  about  one  drop,  this  will  distinctly 
show  a  rose-red  colour.  The  colour  thus  produced  is 
about  three  or  four  times  as  distinct  as  the  one  which  is 
obtained  by  the  addition  of  potassium  ferrocyanide.  Of 
other  metals  which  are  examined  in  this  direction,  we  find 
only  iron  to  be  apt  to  interfere  with  this  reaction,  and  then 
only  when  it  is  present  in  considerable  quantity. 

We  think  that  this  reaction  may  also  be  utilised  as  a 
colorimetric  test  for  the  quantitative  determination  of  small 
quantities  of  copper. 

If  a  substance  contains  so  little  copper  that  the  fluid 
does  not  equal  the  most  faintly  coloured  standard  fluid  in 
intensity  of  colour,  the  assayer  must  endeavour  to  remedy 
the  matter  by  evaporating  till  this  is  the  case.  An  evapo- 
ration is,  however,  avoided,  if  possible,  first  because  of  the 
loss  of  time,  and  also  because  other  precipitations,  carbo- 
nate of  lime,  &c.,  are  apt  to  be  caused  by  it,  and  because, 
when  it  has  to  be  continued  too  long,  so  much  ammonia  is 
apt  to  be  volatilised,  that  a  new  addition  of  it  becomes 
necessary. 

This  method  of  assaying  soon  finds  the  limits  of  its 
accuracy  in  an  increasing  percentage  of  copper  in  the 
assay  sample,  since  with  fluids  rich  in  copper  and  there- 
fore strongly  coloured  blue,  the  errors  of  observation  soon 
amount  to  several  loth.  And  to  seek  then  to  better  one- 
self by  diluting  largely,  yields  no  more  accurate  results, 
since  a  small  error  of  observation  in  determining  the 
intensity  of  the  colour,  is  so  much  the  more  multiplied  in 
the  calculation  of  the  value  by  the  greater  number  of  the 
ounces. 

If  nickel  is  contained  in  the  assay  substance,  the  assay 
cannot  be  conducted  in  the  way  prescribed,  since  the 
nickel  is  extracted  by  the  acids,  and  dissolves  also  in 
caustic  ammonia  with  a  blue  colour.  The  assay  may  also 
become  uncertain  from  the  presence  of  much  manganese, 
cobalt,  or  chromium,  since  they  render  the  hue  of  the  blue 


410  THE   ASSAY   OF    COPPER. 

colour  dingy.  Chromium  may  be  completely  removed  by 
a  slight  boiling  of  the  ammoniacal  fluid  ;  not  so  cobalt. 
The  presence  of  vanadium  or  molybdenum  does  no  harm. 

If  nickel,  or  much  cobalt  and  manganese,  is  contained 
in  the  assay  substance,  the  solution  obtained  by  acids  and 
filtered,  thougli  not  further  diluted,  must  first  be  decom- 
posed by  metallic  iron.  What  is  thrown  down  by  the  iron 
is  collected  on  a  small  filter,  washed  thoroughly,  and  then, 
together  with  the  filter,  treated  with  dilute  nitric  acid. 
When  the  copper  is  all  dissolved,  this  solution  is  supersatu- 
rated with  caustic  ammonia  and  then  managed  as  above. 
With  higher  percentages  of  copper  the  process  of  the 
Swedish  copper  assay  is  used  for  determining  the  value. 
The  precipitation  of  the  copper  may  also  be  performed 
with  sulphuretted  hydrogen  gas. 

Le  Play  removes  the  injurious  influence  of  manganese, 
nickel,  and  cobalt,  by  allowing  the  green  or  violet-coloured 
ammoniacal  solution  to  stand  open  to  the  air  for  several 
weeks  in  a  moderately  warmed  drying  furnace,  whereby  a 
few  variously  coloured  gelatinous  flocks  are  gradually 
deposited,  and  the  fluid,  after  the  addition  of  a  few  drops 
of  ammonia,  then  becomes  pure  blue. 

According  to  Jacquelain  and  Yon  Hubert,  nickel  and 
cobalt  are  in  a  simple  way  rendered  perfectly  harmless  by 
gradually  adding  white  pulverised  marble  to  the  solution 
of  the  assay  substance,  until  the  effervescence  ceases,  and 
then  warming  the  whole  on  the  sand-bath,  whereby  all  the 
copper  is  perfectly  precipitated  as  carbonate,  while  nickel 
and  cobalt  remain  dissolved.  It  is  now  filtered,  washed, 
the  residue  dissolved  in  nitric  acid,  and  the  solution  treated, 
as  already  explained,  with  ammonia.  By  the  addition  of 
potassium  carbonate  to  the  ammoniacal  fluid,  and  heating, 
all  the  manganese  precipitates,  while  the  copper  remains 
dissolved  in  the  excess  of  ammonia,  and  can  be  separated 
from  the  manganese  precipitate  by  filtration.  The  manga- 
nese must  have  been  present  as  oxide  in  the  original  solu- 
tion in  order  that  the  precipitation  by  potassium  carbonate 
may  be  perfect. 

The  assayer    may  convince    himself   whether    nickel 


COLORIMETRIC   ASSAYS.  411 

or  cobalt  is  present,  by  slightly  supersaturating  a  blue 
ammomacal  solution,  obtained  by  the  ordinary  process  of 
assaying,  with  hydrochloric  or  sulphuric  acid,  then  pre- 
cipitating the  copper  completely  with  iron,  filtering  the 
residual  solution,  concentrating  somewhat,  if  necessary, 
and  then  supersaturating  with  ammonia.  If  the  fluid 
remains  colourless,  neither  of  the  two  metals  is  present :  a 
blue  colour  indicates  nickel,  a  red  one  cobalt. 

Sometimes  the  normal  solutions  which  when  freshly 
prepared  appear  azure  blue,  assume  a  greenish  hue,  which 
renders  the  comparison  difficult,  if  not  impossible.  Copper 
nitrate  produces  with  ammonia  a  pure  azure  blue,  copper 
sulphate  a  lilac  colour,  and  copper  chloride  greenish  hues. 
Sulphuric  and  hydrochloric  acid  are  therefore  to  be  avoided 
as  much  as  possible  in  the  solution.  But,  nevertheless,  an 
assay  fluid  may  sometimes — e.g.  by  standing  some  time  in 
the  air,  or  by  slow  filtration — become  green,  in  which  case 
the  colour  is  destroyed  by  a  few  drops  of  nitric  acid,  and 
ammonia  added  anew.  But  sometimes  also  the  greenish 
colour  disappears,  if  the  solution  stands  in  a  covered  vessel 
in  the  air,  or  by  the  addition  of  a  few  drops  of  red  cobalt 
ammonio-oxide. 

According  to  Mliller,  also,  the  colour  stands  in  the 
closest  connection  with  the  quantity  of  ammonia  employed, 
and  it  therefore  leads  to  greater  accuracy  in  the  assay  if  a 
titrated  solution  of  ammonia  is  used,  and  the  volume  of 
the  ammoniacal  fluid  noted,  which,  after  neutralisation  of 
the  residual  free  acid,  is  used  for  the  solution  of  copper. 
The  solution  appears  more  intense  when  viewed  with  a 
grey  background  than  with  a  white  one.  A  greenish  blue 
colouring  becomes  the  more  noticeable  the  greater  is  the 
excess  of  ammonia,  or  the  more  ammoniacal  salts  are  in 
the  solution. 

Dr.  T.  Carnelly  (Manchester  Philosophical  Society), 
gives  the  following  colorhnetric  method  for  determining 
sma]l  quantities  of  copper  : — 

The  method  of  analysis  consists  in  the  comparison  of 
the  purple-brown  colours  produced  by  adding  to  a  solu- 
tion of  potassium  ferrocyanide — first,  a  solution  of  copper 


412  THE   ASSAY   OF   COPPER. 

of  known  strength,  and  secondly,  the  solution  in  which 
the  copper  is  to  be  determined. 

The  solution  and  materials  required  are  as  follows  : — 

(1)  Standard  Copper  Solution. — Prepared  by  dissolv- 
ing  0-393  grm.  of  pure  CuS04,5H20  in  one  litre  of  water, 
1  c.c.  is  then  equivalent  to  Olmgrm.  Cu. 

(2)  Solution    of  Ammonium    Nitrate. — Made   by   dis- 
solving 100  grms.  of  the  salt  in  one  litre  of  water. 

(3)  Potassium    Ferrocyanide    Solution.  —  Containing 
one  part  of  the  salt  in  25  parts  of  water. 

(4)  Two  glass  cylinders ,  holding  rather  more  than  150 
c.c.  each,  the  point  equivalent  to  that  volume  being  marked 
on  the  glass.     They  must,  of  course,  both  be  of  the  same 
tint  and  as  nearly  colourless  as  possible. 

(5)  A  burette,  marked  TL  c.c.,  for  the  copper  solution, 
a  5  c.c.  pipette  for  the    ammonium  nitrate,  and   a  small 
tube  to  deliver  the  potassium  ferrocyanide  in  drops. 

The  following  is  the  method  of  analysis  : — Five  drops 
of  the  potassium  ferrocyanide  are  placed  in  each  cylinder, 
and  then  a  measured  quantity  of  the  neutral  solution  in 
which  the  copper  is  to  be  determined  into  one  of  them 
(A),  and  both  filled  up  to  the  mark  with  distilled  water,  5 
c.c.  of  the  ammonium  nitrate  solution  added  to  each,  and 
then  the  standard  copper  solution  runs  gradually  into  (B), 
till  the  colours  in  both  cylinders  are  of  the  same  depth,  the 
liquid  being  well  stirred  after  each  addition.  The  number 
of  cubic  centimetres  used  are  then  read  off.  Each  cubic 
centimetre  corresponds  to  O'l  mgrm.  of  copper,  from  which 
the  amount  of  copper  in  the  solution  in  question  can  be 
calculated. 

The  solution  in  which  the  copper  is  to  be  estimated 
must  be  neutral,  for  if  it  contains  free  acid  the  latter  lessens 
the  depth  of  colour,  and  changes  it  from  a  purple-brown 
to  an  earthy  brown.  If  it  should  be  acid  it  is  rendered 
slightly  alkaline  with  ammonia,  and  the  excess  got  rid 
of  by  boiling.  The  solution  must  not  be  alkaline,  as  the 
brown  coloration  is  soluble  in  ammonia  and  decomposed 
by  .potash  ;  if  it  is  alkaline  from  ammonia  this  is  remedied 
as  before  by  boiling  it  off,  while  free  potash,  should  it  be 


COLORIMETRIC   ASSAYS.  413 

present,  is  neutralised  by  an  acid  and  the  latter  by  am- 
monia. 

Lead  when  present  in  not  too  large  quantity  has  little 
or  no  effect  on  the  accuracy  of  the  method.  The  precipi- 
tate obtained  on  adding  potassium  ferrocyanide  to  a  lead 
salt  is  white,  and  this,  except  when  present  in  compara- 
tively large  quantity  with  respect  to  the  copper,  does  not 
interfere  with  the  comparison  of  the  colours. 

When  copper  is  to  be  estimated  in  a  solution  contain- 
ing iron  the  following  is  the  method  of  procedure  to  be 
adopted.  To  the  solution  a  few  drops  of  nitric  acid  are 
added  in  order  to  oxidise  the  iron,  the  liquid  evaporated  to 
a  small  bulk,  and  the  iron  precipitated  by  ammonia.  Even 
when  very  small  quantities  of  iron  are  present  this  can  be 
done  easily  and  completely  if  there  is  only  a  very  small 
quantity  of  fluid.  The  precipitate  of  ferric  oxide  is  then 
filtered  off,  washed  once,  dissolved  in  nitric  acid,  and  repre- 
cipitated  by  ammonia,  filtered,  and  washed.  The  iron  pre- 
cipitate is  now  free  from  copper,  and  in  it  the  iron  can  be 
estimated  by  dissolving  in  nitric  acid,  making  the  solution 
nearly  neutral  with  ammonia,  and  determining  the  iron  by 
the  method  given  in  the  paper  before  referred  to.  The 
filtrate  from  the  iron  precipitate  is  boiled  till  all  the  am- 
monia is  completely  driven  off,  and  the  copper  estimated 
in  the  solution  so  obtained  as  already  described. 

2.  JACQUELAIX'S  AND  Vox  HUBERT'S  COLORIMETRIC  ASSAYS. 

Heine's  method,  for  the  reasons  stated,  is  suitable  only 
for  the  determination  of  small  quantities  of  copper.  Jac- 
quelain  has  extended  it  to  the  examination  of  all  cupriferous 
substances,  and  this  process  has  been  further  perfected  by 
Von  Hubert.  According  to  the  latter,  a  solution  of  any 
cupriferous  accurately  weighed  substance  is  prepared, 
mixed  with  ammonia  in  excess,  the  ammoniacal  solution 
(assay  solution)  measured  at  a  definite  volume,  and  a  small, 
likewise  measured  portion  of  the  measured  solution  diluted 
with  water,  until  its  blue  colour  shows  an  equal  intensity 
with  the  blue  colour  of  another  solution  (normal  solution), 


414  THE   ASSAY   OF   COPPER. 

also  cupriferous  and  ammoniacal,  whose  copper  contents 
are  known  once  for  all.  Then,  from  the  quantity  of  water 
added,  in  order  to  make  the  two  fluids  equal  to  each  other 
in  the  intensity  of  their  blue  colours,  the  amount  of  copper 
in  the  substance  under  examination  can  be  determined  by 
calculation. 

The  normal  solution  is  prepared  by  dissolving  -5  of  a 
gramme  of  chemically  pure  copper  in  dilute  nitric  acid, 
adding  ammonia  in  excess,  and  diluting  with  distilled 
water  until  the  whole  at  12°  C.  amounts  to  one  litre=1000 
cubic  centimetres.  The  solution  is  filtered,  and  pre- 
served in  a  flask  provided  with  a  glass  stopper  ground  in 
to  fit  it. 

For  the  preparation  of  the  assay  fluid,  with  substances 
whose  percentage  of  copper  ranges  from  1*5  to  the  highest 
per  cent.,  two  grammes,  and  with  the  poorer  substances 
five  grammes,  are  brought  into  ammoniacal  solution  with 
the  precautions  specified  in  Heine's  assay.  This  solution, 
with  over  5  per  cent,  of  copper,  is  measured  at  two  hun- 
dred cubic  centimetres,  with  2  to  5  per  cent,  of  copper  at 
one  hundred  and  fifty  cubic  centimetres,  and  with  2  per 
cent,  and  under,  at  one  hundred  ;  and  also,  as  may  be 
required,  at  90,  80,  60,  50  c.c.,  according  to  the  intensity 
of  the  fluid.  Only  with  an  extremely  small  quantity  of 
copper  is  the  assay  fluid  evaporated  to  a  smaller  volume, 
in  order  to  be  able  to  conduct  the  colorimetric  test  with 
accuracy. 

The  comparison  of  the  intensity  of  colour  of  the  assay 
fluid  with  the  normal  fluid  is  accomplished  in  two  different 
ways,  according  as  the  former,  when  measured  at  a  defi- 
nite volume,  is  darker  or  lighter  than  the  latter.  This 
can  be  seen  if  a  small  arbitrary  portion  of  each  is  poured 
into  a  glass  tube  of  nine  millimetres  interior  diameter, 
twelve  centimetres  in  length,  and  uniform  thickness,  and 
the  two  tubes  are  held  in  parallel  positions  over  a  piece  of 
white  paper  so  that  they  rest  firmly  on  it,  and  are  inclined 
to  it  at  an  angle  of  about  45°,  and  direct  light  falls  upon 
them.  Shadow  should  not  fall  upon  the  tubes. 

(a).  The  Assay   Fluid    is    Darker   than   the    Normal 


COLOKIMETRIC   ASSAYS.  415 

Solution. — By  means  of  a  pipette,  five  cubic  centimetres  of 
the  normal  solution  are  placed  in  a  glass  tube  closed  at  the 
bottom  and  not  graduated,  and  seven  millimetres  in  interior 
diameter  and  twelve  centimetres  long.  Since  1000  c.c.  of 
the  normal  solution  contain  -5  of  a  gramme  of  copper,  five 
cubic  centimetres  contain  exactly  -0025  and  the  ratio 
5  :  *0025  expresses  once  for  all  the  known  proportion  of 
copper  in  the  normal  solution. 

Five  cubic  centimetres  of  the  definitely  measured  assay 
fluid  are  now  also  placed  in  a  beaker  and  gradually 
diluted  with  water  till  they  show  the  same  intensity  of 
colour  as  the  normal  solution.  In  the  comparison  the 
assay  fluid  must  be  in  a  similar  tube  to  that  containing 
the  normal  solution.  With  richer  proportions  a  greater 
accuracy  is  attained  in  this  comparison  if  the  assay  fluid 
is  so  far  diluted  that  its  intensity  still  appears  as  little  as 
possible  darker  than  that  of  the  normal  solution,  and  then 
water  added  carefully,  and  drop  by  drop,  till  its  intensity 
is  judged  as  little  as  possible  lighter  than  that  of  the  nor- 
mal solution,  whereupon  the  mean  of  the  two  volumes 
noted  is  taken  as  the  correct  value.  The  measuring  of  the 
diluted  assay  fluid  is  performed  in  glass  tubes  of  nine 
millimetres  interior  diameter  and  fifty  centimetres  in 
length,  which  from  their  lower  closed  end  to  the  circular 
mark  designated  by  0,  hold  exactly  five  cubic  centimetres, 
and  from  0  upwards  are  divided  into  cubic  centimetres 
and  tenths. 

If,  for  example,  two  grammes  of  the  assay  substance 
have  been  weighed  out,  the  assay  fluid  measured  at  200 
cubic  centimetres,  and  five  cubic  centimetres  of  it  diluted 
to  8' 2  cubic  centimetres,  in  order  to  obtain  an  equal  inten- 
sity of  colour  between  the  normal  and  assay  fluid,  then  the 
percentage  of  copper,  #,  follows  from  this  according  to  the 
following  chain  of  ratios  : — 


]  00  per  cent. 

200  c.c.  assay  fluid. 

8-2  c.c.  diluted  assay  =  normal  solution. 
•0025  gramme  of  copper  in  normal  solution. 


8%2  per  cent,  of  copper. 


416  THE    ASSAY    OF   COPPER. 

(b).  The  Assay  Fluid  is  Lighter  than  the  Normal  Solution, 
In  this  case  five  cubic  centimetres  of  the  normal  solution 
are  diluted  till  their  intensity  is  equal  to  that  of  the  assay 
solution  that  has  been  measured  at  a  definite  volume,  and 
for  the  comparison  larger  tubes  of  nine  millimetres'  interior 
diameter  are  used. 

If,  for  example,  two  grammes  of  the  assay  substance 
have  been  weighed  out,  150  cubic  centimetres  of  assay 
fluid  obtained  from  it,  and  to  get  the  same  intensity  of 
colour,  five  cubic  centimetres  of  the  normal  solution 
diluted  to  8*4  cubic  centimetres,  the  quantity  of  copper  x 
amounts,  according  to  the  following  chain  of  ratios,  to 
2-205  per  cent. : — 

100  per  cent. 


2 

8-4 

5 


150  c.c.  assay  solution. 
5  c.c.  normal  solution. 
•0025  gramme  of  copper. 


x  =  16-8    j    37-5  =  2-205  per  cent. 

This  assay  is  adapted  for  all  cupriferous  substances, 
since  nickel,  cobalt,  and  manganese,  which  would  influence 
the  result  unfavourably,  can  be  removed  without  particu- 
lar difficulty.  It  is  also  easy  to  be  learned  by  those  less 
practised  in  analytical  operations,  can  be  completed  in  a 
few  hours,  and  is  far  less  expensive  than  the  dry  assay. 
From  two  to  one-tenth  per  cent,  of  copper  can  also  be 
determined  by  it  with  accuracy. 

Heine,  however,  prefers  his  method  when  a  small  per- 
centage of  copper  is  to  be  determined,  since  by  it  even  one 
loth  of  copper  in  the  centner=-03  per  cent.,  can  be  deter- 
mined, and  there  is  less  liability  to  error.  While  in  slag 
assays  with  nine  to  eighteen  loth  of  copper  in  the  centner, 
by  Heine's  method,  errors  of  half  a  loth  are  not  to  be 
avoided,  variations  of  more  than  one  loth  occur  by  Von 
Hubert's  process.  The  latter  works  with  a  too  deeply 
coloured  normal  fluid,  corresponding  to  a  solution  of  over 
fourteen  loth  of  copper  to  one  ounce  of  water,  while  Heine 
does  not  exceed  four  loth.  The  process  is  surer  if  the  fluids 
are  diluted  and  thicker  layers  of  them  compared,  and  thus 
the  hue  made  artificially  deeper,  than  if  small  quantities  of 


VOLUMETRIC   ASSAYS.  417 

stronger  fluids  are  compared  and  the  hue  made  artificially 
lighter  by  comparing  them  in  thinner  layers,  or  especially 
in  tubes,  where  the  light  is  dispersed  and  shade  produced. 
The  comparison  in  oblong  glasses  is  therefore  to  be  pre- 
ferred to  that  in  tubes. 

By  a  comparison  of  Von  Hubert's  assay  with  that  of 
the  Oberhartz,  it  appears  that,  as  Von  Hubert's  experi- 
ments themselves  have  shown,  both  give  equally  accurate 
results  for  substances  not  too  poor  in  copper  (i.e.  contain- 
ing not  less  than  5  per  cent.).  The  Oberhartz  assay 
allows  a  direct  determination  of  the  copper,  requires  less 
apparatus,  is  also  very  simple,  and  can  be  completed  in  a 
shorter  time.  Since  different  individuals  are  differently 
susceptible  to  colours,  and  the  blue  colour  of  the  copper 
ammonio-oxide,  in  consequence  of  causes  yet  unknown, 
sometimes  inclines  more  or  less  to  greenish,  and  thereby 
renders  observation  difficult,  therefore,  for  the  sake  of 
greater  certainty,  though  not  of  greater  accuracy,  those 
assays  by  which  a  determination  of  the  copper  is  possible 
by  weight  should  in  general  be  preferred  to  the  colori- 
metric  methods,  and  this  is  the  case  with  the  Oberhartz 
assay  down  to  two  per  cent.  With  smaller  percentages  the 
colorimetric  assay  must  be  called  to  our  aid.  It  is  not  yet 
settled  that  with  higher  percentages  of  copper  the  prin- 
ciple of  colorimetry  is  a  correct  one  ;  that  is,  that  the  inten- 
sity of  the  colour  is  directly  proportional  to  the  quantity 
of  the  colouring  agent. 

Since  ammoniacal  solutions  poor  in  copper  often  show 
a  dash  of  green  colour,  Yon  Hubert  prepares  a  normal 
solution  for  such  by  dissolving  one  decigramme  of  copper 
and  diluting  to  one  litre  of  fluid. 

b.   Volumetric  Copper  Assays. 
FLECK'S  MODIFICATION  OP  MOHR'S  METHOD.* 

The  proposal  to  take  the  action  of  solution  of  potas- 
sium cyanide  on  ammoniacal  solution  of  copper,  as  the 

*  This  process  is  given  by  Fresenius,  condensed  from  the  '  Polytechn  Cen- 
tralbl.'  1856,  1313. 

E  E 


418  THE   ASSAY   OF   COPPER. 

foundation  of  a  method  for  estimating  copper,  is  due  to 
Carl  Mohr.* 

The  azure  blue  colour  disappears,  Cu2Cy,NH4Cy  and 
KG  are  formed,  while  1  eq.  of  cyanogen  is  separated,  which, 
acting  on  the  free  ammonia,  gives  urea,  urea  oxalate,  am- 
monium cyanide,  and  ammonium  formiate  (Liebig).f 

The  decomposition  is  not  always  the  same  :  the  quan- 
tity and  degree  of  concentration  of  the  ammonia  have  a 
marked  influence  on  it,  from  which  it  appears  that  neutral 
ammonium  salts  also  affect  the  results. 

In  carrying  out  this  estimation  according  to  the  direc- 
tions of  Mr.  Parkes,  a  solution  of  potassium  cyanide  is  slowly 
added  to  a  blue  ammoniacal  solution  of  copper,  when  the 
latter  gradually  loses  its  colour,  and  finally  becomes  quite 
colourless  ;  upon  this  chemical  reaction  the  estimation  of 
copper  by  cyanide  of  potassium  depends.  By  ascertaining 
by  direct  experiment  the  amount  of  potassium  cyanide 
solution  required  to  discharge  the  colour  in  an  ammoniacal 
solution  containing  a  given  weight  of  copper,  it  is  easy  by 
a  comparative  experiment  to  determine  the  amount  of 
copper  in  a  given  weight  of  ore. 

For  the  preparation  of  the  standard  solution  2,000 
grains  of  fused  potassium  cyanide  are  to  be  dissolved  in 
two  quarts  of  water,  to  produce  a  solution  of  which  1,000 
grains  measure  will  be  equal  to  about  ten  grains  of  metallic 
copper.  The  solution  should  be  preserved  in  green  glass 
stoppered  bottles,  and  kept  as  much  as  possible  away  from 
the  light :  it  is  liable  to  a  slow  decomposition,  which  will 
necessitate  the  standard  being  checked  at  intervals  of  one 
or  two  weeks.  In  order  to  standardise  the  solution,  a 
burette,  holding  1,000  grains  measure,  is  filled  to  the  zero 
mark,  and  a  piece  of  pure  electrotype  copper,  previously 
cleaned  by  means  of  dilute  nitric  acid,  washed  and  dried, 
is  accurately  weighed.  About  eight  grains  may  be  con- 
veniently taken  ;  this  is  dissolved  in  a  pint  flask  by  dilute 
nitric  acid,  and,  after  the  energy  of  the  first  action  has  sub- 

*  Annal.  d.  Chem.  u.  Pharm.  94,  198 ;  Fr.  Mohr's  Lehrbuch  der  Titrier- 
methode,  2,  91. 

t  Annal.  d.  Chem.  u.  Pharm.  95,  118. 


VOLUMETRIC   ASSAYS.  419 

sided,  the  solution  is  warmed  and  ultimately  boiled  to  expel 
all  the  nitrous  acid  fumes.  It  is  diluted  with  cold  water 
to  the  bulk  of  nearly  half-a-pint,  treated  with  ammonia  in 
excess,  and  to  the  deep  blue  solution  the  cyanide  is  added 
from  the  burette  until  the  colour  is  so  nearly  discharged 
that  a  faint  lilac  tint  only  remains.  This  will  generally 
become  quite  bleached  on  standing  at  rest  for  a  short  time, 
so  that  the  cyanide  must  not  be  added  too  hastily  towards 
the  end  of  the  operation.  It  will  be  advisable  to  control 
the  standard  by  a  second  experiment  upon  another  weighed 
portion  of  copper,  and  to  stop  short  of  bleaching  entirely 
the  faint  lilac  tint  of  the  solution.  A  piece  of  white  paper 
folded  and  placed  under  and  behind  the  flask  during  the 
decolorisation,  will  aid  in  recognising  the  proper  tint  of 
the  solution. 

In  applying  this  process  to  the  examination  of  copper 
ores,  a  known  weight  of  the  finely-powdered  sample  is 
introduced  into  a  beaker  provided  with  a  glass  cover,  and 
moistened  with  strong  sulphuric  acid  ;  strong  nitric  acid  is 
then  added,  and  the  whole  digested  on  a  sand-bath  until 
nitrous  fumes  are  no  longer  given  off.     Should  a  small 
quantity  of  sulphur  be  separated  in  the  treatment  of  py- 
ritic  ores,  the  small  globules  may  be  taken  out,  burnt,  and 
the  residual  copper  dissolved  in  a  few  drops  of  nitric  acid 
and  mixed  with  the  remainder.       Water  is  now   to   be 
added  and  left  in  contact  for  a  short  time  to  extract  all 
the  metallic  salt  from  the  insoluble  residue,  which  need  not 
be  filtered  off;  and  so,  likewise,  when  ammonia  is  added 
in  the  next  place,  any  ferric  oxide  which  may  thus  be 
precipitated  is  left  in  the  solution,  for  it  is  apt  to  contain  a 
small  proportion  of  copper  when  first  thrown  down  ;  but 
this  is  entirely  removed  by  the  potassium  cyanide  later  in 
the  experiment. 

When  the  ore  contains  much  iron  it  is  considered 
desirable  to  remove  the  hydrated  peroxide  by  filtration,  in 
order  to  be  enabled  to  determine  with  greater  precision  the 
last  effects  of  the  potassium  cyanide  ;  and  in  the  event  of 
requiring  to  know  the  amount  of  iron  present  in  the  ore, 
the  precipitated  ferric  oxide  on  the  filter  is  redissolved  in 

E    E   2 


420  THE   ASSAY   OF   COPPER, 

dilute  sulphuric  acid,  reduced  to  the  state  of  ferrous  oxide 
by  metallic  zinc,  and  then  tested  in  the  usual  way  with  a 
standard  solution  of  potassium  bichromate. 

The  metals  which  interfere  with  this  mode  of  valuing 
copper  ores,  are  silver,  nickel,  cobalt,  and  zinc.  The  first 
may  readily  be  separated  by  adding  a  few  drops  of  hydro- 
chloric acid  to  the  original  solution  :  the  other  metals  may 
be  excluded  by  following  one  of  the  methods  pointed  out 
by  the  author  for  that  purpose. 

Fleck  proposes  the  following  modification  in  this  pro- 
cess : — 

Instead  of  caustic  ammonia,  use  a  solution  of  ammo- 
nium sesquicarbonate  (1  in  10),  warm  the  mixture  to 
about  60°,  and  in  order  to  render  the  end  reaction  plainer, 
add  2  drops  of  solution  of  potassium  ferrocyanide  (1  in 
20) :  the  blue  colour  of  the  solution  is  not  altered  by  this 
addition,  nor  is  its  clearness  affected.  The  value  of  the 
potassium  cyanide  solution  is  first  determined  by  means  of 
copper  solution  of  known  strength,  and  it  is  then  employed 
on  the  copper  solution  to  be  examined.  On  dropping  the 
potassium  cyanide  into  the  blue  solution  warmed  to  60°, 
the  odour  of  cyanogen  is  plainly  perceptible,  and  the 
colour  gradually  disappears.  As  soon  as  the  ammoniacal 
double  salt  of  copper  is  destroyed,  the  solution  becomes 
red  from  the  -  formation  of  copper  ferrocyanide,  without 
any  precipitate  appearing,  and  with  the  addition  of  a 
final  drop  of  potassium  cyanide  this  red  colour  in  its  turn 
vanishes,  so  that  the  fluid  now  appears  quite  colourless. 

The  method  thus  modified  yields,  it  is  true,  better,  but 
still  only  approximate  results.*  Where  such  are  good 
enough,  the  method  is  certainly  convenient. 


*  In  six  experiments,  in  which  he  had  purposely  added  different  quantities 
of  carbonate  of  ammonia,  Fleck  used  for  100  c.c.  copper  solution,  in  the 
minimum  15'2,  in  the  maximum  15-75,  in  the  mean  15'46  c.c.  potassium  cyanide 
solution. 


VOLUMETKIC   ASSAYS.  421 

E.  0.  BROWN'S  METHOD  BY  SODIUM  HYPOSULPHITE. 

The  process  described  by  Mr.  E.  0.  Brown  is  particu- 
larly applicable  to  the  determination  of  copper  in  gun- 
metal,  brass,  and  other  alloys  which  contain  no  large 
amounts  of  iron  and  lead.  It  is  founded  on  the  reactions 
between  salts  of  copper  and  the  neutral  iodides,  and  on 
the  conversion  of  the  liberated  iodine  into  hydriodic  and 
tetrathionic  acids  by  a  standard  solution  of  sodium  hypo- 
sulphite. 

These  reactions  may  be  thus  expressed  : — 

2(CuO,A)  +  2KI  =  Cu2I  +14-  2(KO,A) 
I  +  2(NaO,S202)  =  Nal  +  NaO,S405 

The  completion  of  the  second  reaction  is  manifested 
by  the  bleaching  effect  produced  upon  the  blue  iodide  of 
starch  by  the  addition  of  the  hyposulphite.  A  convenient 
strength  of  solution  for  this  purpose  may  be  made  by  dis- 
solving 1,300  grains  of  the  crystallised  salt  in  two  quarts 
of  water.  The  potassium  iodide  must  be  free  from  iodate  ; 
and  a  clear  solution  of  starch  employed. 

From  eight  to  ten  grains  of  the  copper  or  alloy  are 
dissolved  in  dilute  nitric  acid,  and  the  red  nitrous  fumes 
expelled  by  boiling.  The  copper  nitrate  is  converted  into 
acetate  by  adding  sodium  carbonate  until  a  portion  of 
copper  remains  precipitated,  and  then  re-dissolving  in 
acetic  acid.  The  solution  is  diluted  with  water,  and  about 
60  grains  of  potassium  iodide  in  the  form  of  crystals 
dropped  into  the  flask,  and  allowed  to  dissolve.  The 
standard  solution  of  sodium  hyposulphite  is  now  poured 
in  from  a  burette,  until  the  greater  part  of  the  dark- 
coloured  free  iodine  disappears.  A  little  of  the  starch 
solution  is  now  added  to  make  its  presence  more  apparent, 
and  the  addition  of  the  hyposulphite  continued  until  the 
bleaching  is  completed,  when  the  pale  yellow  colour  of  the 
copper  subiodide  will  alone  be  visible.  The  amount  of 
copper  in  the  ore  or  alloy  is  calculated  from  the  number 
of  divisions  indicated  upon  the  burette. 

Copper  ores  containing  much  iron  (which  interferes  by 


422 


THE   ASSAY    OF    COPPER. 


reason  of  the  dark  red  colour  of  the  acetate)  may  be  dis- 
solved in  nitric  acid,  and  treated  with  sulphuretted  hydro- 
gen to  precipitate  the  copper,  the  sulphide  being  collected 
on  a  filter,  washed,  and  re-dissolved  in  nitric  acid  to  pro- 
duce a  solution  suitable  for  testing  by  this  process.  Or 
the  hyposulphite  may  itself  be  employed  to  furnish  a  pre- 
cipitate of  copper  disulphide. 

Dr.  Wolcott  Gibbs  recommends  the  electrolytic  precipi- 
tation of  copper  and  nickel  as  a  method  of  analysis.  He 
says  : 

The  precipitation  of  copper  byzinc,in  a  platinum  vessel, 
with  the  precautions  recommended  by  Fresenius,  leaves 
nothing  to  be  desired,  so  far  as  accuracy,  ease,  and  rapid- 
ity of  execution  are  concerned.  The  method  labours,  how- 
ever, under  a  single  disadvantage — the  introduction  of 
zinc  renders  it  difficult,  or  at  least  inconvenient,  to  deter- 
mine with  accuracy  other  elements  which  may  be  present 
with  the  copper.  It  has  occurred  to  me  that  this  diffi- 
culty might  be  overcome,  the  principle  of  the  method 
being  still  retained,  by  precipitating  the  copper  by  electro- 
lysis with  a  separate  rheomotor.  The  following  numerical 
results,  which  are  due  to  Mr.  E.  V.  M'Candless,  will  satis- 
factorily show  the  advantages  of  the  method  for  the  par- 
ticular cases  in  which  it  is  desirable  to  employ  it.  The 
copper  was  in  each  case  in  the  form  of  sulphate :  the  de- 
position took  place  in  a  small  platinum  capsule,  which  was 
made  to  form  the  negative  electrode  of  a  Bunsen's  battery 
of  one  or  two  cells,  in  rather  feeble  action.  The  positive 
electrode  consisted  of  a  stout  platinum  wire,  plunged  into 
the  surface  of  the  solution  of  copper  at  its  centre.  The 
following  table  gives  the  results  obtained  in  the  analysis  of 
pure  copper  sulphate  :- — 


Number 

Salt  taken 

Copper  found 

Percentage 

1 

1-2375 

0-3145 

25-41 

2 

0-4235 

0-1075 

25-38 

3 

1-0640 

0-2705 

25-42 

4 

1-3580 

0-3440 

25-33 

5 

0-5665 

0-1450 

25-59 

6 

0-4735 

0-1205 

25-48 

VOLUMETRIC   ASSAYS.  423 


In  seven  determinations  of  copper  in  the  alloy  of 
copper  and  nickel  employed  by  the  Government  for  small 
coins  the  following  results  were  obtained  : — 


Number 

Weight  of  Alloy 

Copper 

Percentage 

i 

0-4160 

0-3640 

87-50 

2 

0-6180 

0-5410 

87-54 

3 

0-4600 

0-4090 

88-91 

4 

0-5120 

0-4481 

87-51 

5 

0-4220 

0-3693 

87-51 

6 

0-2525 

0-2225 

88-11 

7  - 

0-3705 

0-3255 

87-85 

i 

The  percentage  of  copper  required  by  the  formula 
CuO,S03  5H20  is  25-42,  while  the  Government  standard 
alloy  of  nickel  and  copper  contains  87 '50  per  cent,  of 
copper.  The  time  required  for  precipitation  varied  from 
one  to  three  hours,  the  separation  of  the  last  traces  of 
copper  being  in  each  case  determined  by  testing  a  drop  of 
the  liquid  upon  a  porcelain  plate  with  sulphuretted  hydro- 
gen water.  The  copper  after  precipitation  was  washed 
with  distilled  water,  dried  in  vacuo  over  sulphuric  acid, 
and  weighed  with  the  platinum  vessel.  The  only  precau- 
tion necessary  is  to  regulate  the  strength  of  the  current  so 
that  the  copper  may  be  precipitated  as  a  compact  and 
bright  metallic  coating,  and  to  dry  as  quickly  as  possible. 
When  the  copper  is  thrown  down  in  a  spongy  condition, 
it  not  only  oxidises  rapidly,  but  it  is  impossible  to  wash 
out  the  last  traces  of  foreign  matter  contained  in  the  solu- 
tion. This  is  well  shown  by  No.  3  and  No.  4  of  the  second 
series,  in  both  of  which  cases  the  copper  was  precipitated 
too  rapidly.  The  solution  from  which  the  copper  has 
been  deposited  contains  the  other  elements  present  in  the 
original  substance.  It  may  be  easily  poured  off  without 
loss,  and  the  washings  added. 

Mr.  J.  M.  Merrick  has  communicated  to  the  '  Chemical 
News  '  a  simple  and  accurate  process  of  assaying  copper 
in  pyrites  based  on  this  method.  Treat  the  pyrites  with 
nitric  acid  to  complete  oxidation  of  the  sulphur,  evaporate 


424  THE   ASSAY   OF   COPPER. 

to  dryness,  and  ignite  gently ;  then  treat  with  a  small 
amount  of  boiling  water,  and  sufficient  ammonia  to  preci- 
pitate and  re-dissolve  the  copper.  Filter  the  blue  solution 
from  the  silica,  iron  oxide,  &c.,  wash  the  filter,  concentrate 
the  washings  if  need  be,  make  the  filtrate  sharply  acid 
with  sulphuric  acid,  and  plate  out  the  copper  on  the 
inside  of  a  platinum  dish  which  is  made  the  cathode  of  a 
battery  of  the  two  small  Grove's  cells,  the  anode  being  a 
stout  platinum  wire  hung  in  the  solution.  For  a  tolerably 
close  result — generally  sufficient  in  technical  work — the 
solution  in  ammonia  may  be  omitted,  and  the  copper 
directly  plated  over  from  the  solution  filtered  from  the 
silica,  &c.  For  the  exact  determination  of  very  minute 
quantities  of  copper  no  method  can  approach  it. 

The  nickel  may  be  determined  by  electrolysis  in  the 
same  manner  as  copper,  the  solution  employed  being  the 
sulphate  rendered  ammoniacal  with  excess  of  free  am- 
monia. Mr.  M'Candless  obtained  in  two  determinations  in 
a  commercial  sample  91*36  and  91-60  per  cent,  of  nickel. 
In  both  cases  the  nickel  was  thrown  down  completely  as 
a  bright,  coherent,  metallic  coating  upon  the  platinum. 

Assay  of  Copper  Pyrites. — The  following  method  of 
treating  copper  pyrites  has  been  found  more  advantageous 
than  the  ordinary  process  of  oxidising  the  mineral  with 
aqua  regia,  and  subsequently  evaporating  the  solution  re- 
peatedly with  hydrochloric  acid,  or  with  sulphuric  acid,  to 
expel  the  last  traces  of  nitric  acid.  It  is  thus  described 
by  Mr.  F.  P.  Pearson  in  the  '  Chemical  News ' : — 

Place  a  weighed  quantity  of  the  powdered  mineral,  to- 
gether with  some  potassium  chlorate,  in  a  porcelain  dish. 
(Five  grammes  of  a  variety  of  a  pyrites  containing  about 
18  per  cent,  of  copper  was  found  to  be  enough  for  one 
analysis ;  and  a  quantity  of  potassium  chlorate  equal  to  a 
small  teaspoonful  was  added  to  the  ore.)  Invert  a  small 
glass  funnel  with  bent  stem  in  the  dish  above  the  pyrites, 
and  pour  upon  the  latter  rather  more  ordinary  strong 
nitric  aci<J  than  would  be  sufficient  to  completely  cover 
the  powder.  Place  the  dish  upon  a  water-bath,  and,  from 
time  to  time,  throw  into  it  small  quantities  of  potassium 


ASSAY   OF   COPPER   PYRITES.  425 

•chlorate.  The  doses  of  the  chlorate  must  be  repeated  at 
frequent  intervals,  until  free  sulphur  can  no  longer  be  seen 
in  the  dish.  If  need  be,  add  nitric  acid,  also,  from  time  to 
time,  to  replace  that  lost  by  evaporation. 

As  a  general  rule,  it  is  safer  and  more  convenient  to 
heat  the  mixture  on  a  water-bath  than  upon  sand,  though 
the  oxidation  of  sulphur  can  be  effected  more  easily  and 
quickly  when  the  mixture  of  nitric  acid  and  chlorate  is 
heated  to  actual  boiling  than  at  the  temperature  obtain- 
able by  means  of  a  water-bath.  When  the  last  particles 
of  sulphur  have  been  destroyed,  remove  the  inverted  funnel 
from  the  dish,  rinse  it  with  water,  and  collect  the  rinsings 
in  a  beaker  by  themselves.  Allow  the  liquid  in  the  evapo- 
rating-dish  to  become  cold,  pour  upon  it  a  quantity  of 
ordinary  strong  hydrochloric  acid  rather  larger  than  the 
quantity  of  nitric  acid  taken  at  first,  evaporate  the  mixed 
solution  to  dryness,  and  heat  the  dry  residue  to  render 
silica  insoluble,  in  case  any  silica  be  present. 

Pour  water  upon  the  cold  residue,  and,  without  filter- 
ing the  liquor,  wash  the  contents  of  the  dish  into  the 
beaker  which  contains  the  rinsings  of  the  funnel.  Heat 
the  liquid  in  the  beaker  nearly  to  boiling,  add  to  it  about 
25  c.c.  of  a  strong  aqueous  solution  of  ferrous  sulphate 
slightly  acidulated  with  sulphuric  acid,  and  keep  the  mix- 
ture at  a  temperature  near  boiling  during  four  or  five 
minutes,  in  order  to  destroy  the  small  quantity  of  nitric 
acid  which  may  have  escaped  decomposition  in  spite  of 
the  dry  evaporation  with  hydrochloric  acid. 

The  ferrous  salt  seldom  acts  instantaneously,  but  the 
reducing  action  proceeds  rapidly  and  satisfactorily  when 
once  begun.  If  need  be,  add  more  of  the  ferrous  solution, 
little  by  little,  until  the  entire  contents  of  the  beaker 
become  dark-coloured  or  black,  and  no  more  gas  is  disen- 
gaged. 

In  order  to  be  sure  that  all  the  nitric  acid  has  been 
reduced,  it  is  as  well,  after  the  mixture  of  liquid  and  solu- 
tion of  ferrous  sulphate  has  been  duly  heated,  to  place 
a  drop  of  the  mixture  upon  porcelain,  and  test  it  with 
potassium  ferrocyanide.  In  general,  however,  the  colora- 


426  THE   ASSAY   OF   COPPER. 

tion  of  the  liquid  in  the  beaker,  due  to  the  formation  of 
nitrous  or  hyponitric  acid,  will  be  a  sufficient  indication 
that  the  sulphate  of  iron  has  done  its  work.  The  nitrous 
fumes  quickly  disappear  from  the  liquid  at  a  subsequent 
stage  of  operations  when  metallic  iron  is  immersed  in  the 
solution. 

When  enough  of  the  ferrous  sulphate  has  been  added,, 
filter  the  mixed  solution  into  a  wide  beaker,  precipitate  the 
copper  in  the  metallic  state  upon  a  sheet  of  iron  in  the 
usual  way,  and  ignite  the  copper  in  a  porcelain  crucible,, 
in  a  current  of  hydrogen,  before  weighing  it. 

By  means  of  the  ferrous  salt,  the  last  traces  of  nitric 
acid  may  be  got  rid  of  far  more  quickly,  conveniently,  and 
certainly  than  by  the  old  system  of  evaporating  the  pyrites- 
solution  with  several  successive  portions  of  hydrochloric 
acid.  By  treating  the  pyrites  with  potassium  chlorate  and 
nitric  acid,  it  is  easy  to  oxidise  and  dissolve  every  particle 
of  the  sulphur  in  the  mineral,  so  that  no  portion  of  the 
latter  can  escape  decomposition  by  becoming  enveloped 
in  free  sulphur.  When  aqua  regia  is  used,  on  the  other 
hand,  or  a  mixture  of  potassium  chlorate  and  hydrochloric 
acid,  a  certain  proportion  of  sulphur  almost  invariably 
remains  undissolved,  and  might  easily  enclose  portions  of 
the  mineral,  so  as  to  protect  them  from  the  solvent  action 
of  the  acids. 

For  the  Determination  of  Copper  and  Sulphur  in  Copper 
Pyrites,  B.  Fresenius  ('  Zeitschrift  flir  Anal.  Chemie,'  1877, 
p.  355),  proceeds  as  follows  : — 

'After  drying  at  100°  C.,  and  carefully  preparing  the 
sample,  he  takes  for  the  determination  of  the  copper  & 
grm.  pyrites,  heats  with  6  to  7  c.c.  hydrochloric  acid  (sp. 
gr.  1*17),  adding  gradually  nitric  acid  of  sp.  gr.  1*37,  till 
no  more  action  ensues,  and  digests  then  for  some  hours 
at  a  gentle  heat.  The  contents  of  the  flask  are  poured 
into  a  porcelain  capsule,  the  flask  is  twice  rinsed  out  with 
10  c.c.  hydrochloric  acid  (sp.  gr.  1*12)  into  the  capsule, 
and  is  then  set  aside.  The  contents  of  the  capsule  are 
then  evaporated  almost  to  dry  ness  on  the  water-bath, 
20  c.c.  hydrochloric  acid  of  sp.  gr,  1*12  are  added,  heated, 


SULPHUR  IN  COPPER  PYRITES.  427 

mixed  with  water,  and  filtered  into  a  boiling-flask  holding 
•500  c.c.  The  solution-flask  is  also  rinsed  upon  the  filter 
with  water.  The  filter  is  dried,  incinerated  in  a  porcelain 
crucible,  and  the  residue  (in  part  lead  sulphate)  is  treated 
with  1  c.c.  aqua  regia,  evaporated  to  dryness,  the  residue 
treated  with  5  c.c.  hydrochloric  acid  (1-12  sp.  gr.)  slightly 
diluted,  and  the  solution,  which  may  contain  a  little 
copper,  is  filtered  into  the  main  solution.  The  solution  is 
then  precipitated  with  sulphuretted  hydrogen  at  70°  C., 
the  precipitate  is  filtered,  washed,  dried,  mixed  with  the 
thoroughly  burnt  ash  of  the  filter,  heated  with  5  c.c.  nitric 
acid  (of  sp.  gr.  1-2),  filtered  and  washed.  The  filter  is  in- 
cinerated, the  small  residue  is  again  heated  with  2  c.c.  of 
the  same  nitric  acid,  diluted,  filtered  to  the  main  solution 
and  washed.  The  solution  is  mixed  with  12  c.c.  dilute 
sulphuric  acid  (1  part  acid  to  5  water)  evaporated  to 
expel  nitric  acid,  filtered  to  remove  lead  sulphate,  washing 
with  water  acidulated  with  sulphuric  acid.  The  copper 
is  then  precipitated  with  sulphuretted  hydrogen  at  70°  C.y 
the  precipitate  washed,  dried,  ignited  along  with  the  ash 
of  the  filter  in  a  current  of  hydrogen,  and  weighed  as 
copper  sulphide. 

'For  the  determination  of  sulphur  the  author  fuses 
.',  grm.  of  the  sample  with  10  parts  of  a  mixture  of  2 
parts  sodium  carbonate  and  1  part  potassium  nitrate,  and 
determines  the  sulphuric  acid  formed.  For  burnt  ores 
he  uses  4  parts  sodium  carbonate  to  1  part  of  potassium- 
nitrate.' 

ESTIMATION  OP  COPPER  IN  THE  MANSFELD  ORES  BY  DR. 
STEINBECK'S  PROCESS. — This  method  embraces  three  distinct 
operations,  viz. : — 1.  The  extraction  of  the  copper  from 
the  ore ;  2.  The  separation ;  3.  The  quantitative  estima- 
tion of  that  metal. 

1.  The  Extraction  of  the  Copper  from  the  Ore. — A  proof 
centner,  equal  to  5  grammes  of  pulverised  ore,  is  put  into 
a  flask,  and  there  is  poured  over  it  a  quantity  of  from  40 
to  50  c.c.  of  crude  hydrochloric  acid,  of  a  specific  gravity 
of  1*16,  whereby  all  carbonates  are  converted  into  chlorides, 
while  carbonic  acid  is  expelled.  After  awhile,  there  is  added 


428  THE   ASSAY   OP    COPPER. 

to  the  fluid  in  the  flask  6  c.c.  of  a  normal  nitric  acid,  pre- 
pared by  mixing  equal  bulks  of  water  and  pure  nitric  acid 
of  1*2  sp.  gr.  As  regards  certain  ores,  however,  specially 
met  with  in  the  district  of  Mansfeld,  some,  having  a  very 
high  percentage  of  sulphur  and  bitumen,  have  to  be  roasted 
previous  to  being  subjected  to  this  process  ;  and  others, 
again,  require  only  1  c.c.  of  nitric  acid  instead  of  6.  The 
flask  containing  the  assay  is  digested  on  a  well-arranged 
sand-bath  for  half  an  hour,  and  the  contents  only  boiled 
for  about  fifteen  minutes,  after  which  the  whole  of  the 
copper  occurring  in  the  ore,  and  all  other  metals,  are  in 
solution  as  chlorides.  The  blackish  residue,  consisting  of 
sand  and  schist,  has  been  proved  by  numerous  experi- 
ments to  be  either  entirely  free  from  copper,  or  at  the 
most  only  O01  to  O'Oo  per  cent,  has  been  left  undissolved. 

The  extraction  of  the  copper  from  the  ore,  according 
to  this  method,  is  complete  even  in  the  case  of  the  best 
quality  of  ore,  which  contains  about  14  per  cent,  of  metal ; 
while,  at  the  same  time,  the  very  essential  condition  for 
the  proper  and  complete  separation  of  the  metal,  viz.,  the 
entire  absence  of  nitric  acid,  or  any  of  the  lower  degrees 
of  oxidation  of  nitrogen,  is  fully  complied  with. 

2.  Separation  of  the  Copper. — The  solution  of  metallic 
and  earthy  chlorides,  and  some  free  hydrochloric  acid, 
obtained  as  just  described,  is  separated  by  filtration  from 
the  insoluble  residue,  and  the  fluid  run  into  a  covered 
beaker  of  about  400  c.c.  capacity  ;  in  this  beaker  has 
been  previously  placed  a  rod  of  metallic  zinc,  weighing 
about  50  grammes,  and  fastened  to  a  piece  of  stout 
platinum  foil.  The  zinc  to  be  used  for  this  purpose 
should  be  as  much  as  possible  free  from  lead,  and  at  any 
rate  not  contain  more  than  from  0*1  to  0*3  per  cent,  of  the 
latter  metal.  The  precipitation  of  the  copper  in  the  me- 
tallic state  sets  in  already  during  the  filtration  of  the  warm 
and  concentrated  fluid,  and  is — owing  chiefly  to  the  com- 
plete absence  of  nitric  acid — completely  finished  in  from 
half  to  three-quarters  of  an  hour  after  the  beginning  of 
the  filtration.  If  the  fluid  be  tested  with  sulphuretted 
hydrogen,  no  trace  even  of  copper  will  be  detected  ;  the 


STEINBECK'S  PROCESS.  429 

spongy  metal  partly  covers  the  platinum  foil,  partly  floats 
about  in  the  liquid,  and,  in  case  either  the  ore  itself  or 
the  zinc  applied  in  the  experiment  contained  lead,  small 
quantities  of  that  metal  will  accompany  the  precipitated 
copper.  After  the  excess  of  zinc  (for  an  excess  must  be 
always  employed)  has  been  removed,  the  spongy  metal  is 
repeatedly  and  carefully  washed  by  decantation  with  fresh 
water,  which  need  not  be  distilled,  and  care  is  taken  to 
collect  together  every  particle  of  the  spongy  mass. 

3.  Quantitative  Estimation  of  the  Precipitated  Copper. — 
To  the  spongy  metallic  mass  in  the  beaker,  wherein  the 
platinum  foil  is  left,  since  some  of  the  metal  adheres  to  it, 
8  c.c.  of  the  normal  nitric  acid  are  added,  and  the  copper 
is  dissolved,  by  the  aid  of  moderate  heat,  as  copper 
nitrate  ;  in  the  event  of  any  small  quantity  of  lead  being 
present,  it  will  of  course  be  contaminated  with  lead 
nitrate. 

When  copper  ores  are  dealt  with  which  contain  above 
6  per  cent,  of  copper,  which  may  be  sufficiently  judged 
from  the  larger  bulk  of  the  spongy  mass  of  precipitated 
metal,  16  c.c.  of  nitric  acid,  instead  of  8,  are  employed  for 
dissolving  the  spongy  metallic  mass.  The  solution  thus 
obtained  is  left  to  cool,  and  next,  immediately  before  titra- 
tion  with  potassium  cyanide,  mixed  with  10  c.c.  of  normal 
solution  of  ammonia,  prepared  by  diluting  1  volume  of 
liquid  ammonia,  sp.  gr.  0*93,  with  2  volumes  of  distilled 
water. 

In  the  case  of  ores  which  yield  over  0  per  cent,  of 
copper,  and  when  a  double  quantity  of  normal  nitric  acid 
has  consequently  been  used,  the  solution  of  copper  in 
nitric  acid  is  diluted  with  water,  and  made  to  occupy  a 
bulk  of  100  c.c.  ;  this  bulk  is  then  divided  exactly  into 
two  portions  of  50  c.c.  each,  and  each  of  these  separately 
mixed  with  10  c.c.  of  the  liquid  ammonia  solution  just 
alluded  to,  and  the  copper  therein  volumetrically  deter- 
mined. The  deep  blue-coloured  solution  of  oxide  of 
copper  in  ammonia  only  contains,  besides  ammonium 
nitrate,  any  lead  which  might  have  been  dissolved  having 
been  precipitated  as  hydrated  lead  oxide,  which  does  not 


430  THE   ASSAY   OF    COPPER. 

interfere  with  the  titration  with  potassium  cyanide.  The 
solution  of  the  last-named  salt  is  so  arranged  that  1  c.c. 
thereof  exactly  indicates  0*005  grm.  of  copper.  Since, 
for  every  assay,  5  grms.  of  ore  have  been  taken,  1  c.c.  of 
the  titration  fluid  is,  according  to  the  following  proportion 
—5  :  0-005  ::  100  :  O'l — equal  to  O'l  per  cent,  of  copper  ; 
it  hence  follows  that,  by  multiplying  the  number  of  the 
c.c.  of  potassium  cyanide  solution  used  to  make  the  blue 
-colour  of  the  copper  solution  disappear,  by  O'l,  the  per- 
centage of  copper  contained  in  the  ore  is  immediately 
indicated. 

As  may  be  imagined,  at  the  laboratory  of  the  mine- 
owners  at  Eisleben,  such  a  large  number  of  assays  are 
daily  executed  that,  in  this  case,  there  can  be  no  reason  to 
fear  a  deterioration  of  the  cyanide  solution,  of  which  large 
quantities  are  used  and  often  fresh  made  ;  but  for  security's 
sake  the  solutions  are  purposely  tested  for  control  at  least 
•once  every  week.  According  to  the  described  plan,  six 
assays  can  be  made  within  4  hours  ;  and  during  a  work- 
ing day  of  from  7^  to  8  hours,  twenty  assays  have  been 
often  quite  satisfactorily  made  by  the  umpires,  as  well  as 
by  the  workmen  at  Eisleben. 

Special  Observations  on  this  Method. — Dr.  Steinbeck 
-considered  it  necessary  to  test  this  method  specially,  in 
order  to  see  what  influence  is  exercised  thereupon  by  (1) 
ammonium  nitrate,  (2)  caustic  ammonia,  (3)  the  presence  of 
lead  oxide.  The  copper  used  to  perform  the  experiments 
for  this  purpose  was  pure  metal,  obtained  by  galvano- 
plastic  action,  and  was  ignited  to  destroy  any  organic 
matter  which  might  accidentally  adhere  to  it,  and,  next, 
cleaned  by  placing  it  in  dilute  nitric  acid.  Five  grammes 
•of  this  metal  were  placed  in  a  litre  flask,  and  dissolved  in 
266-6  c.c.  of  normal  nitric  acid,  the  flask  and  contents 
gently  heated,  and,  after  cooling,  the  contents  diluted  with 
water,  and  thus  brought  to  a  bulk  of  1,000  c.c.  exactly. 
Thirty  c.c.  of  this  solution  were  always  applied  to  test  and 
titrate  one  and  the  same  solution  of  potassium  cyanide 
under  all  circumstances.  When  5  grammes  of  ore,  con- 
taining on  an  average  3  per  cent,  of  copper,  are  taken  for 


STEINBECK'S'  PROCESS.  431 


•assay,  that  quantity  of  copper  is  exactly  equal  to  0'15 
gramme  of  the  chemically  pure  copper.  The  quantity  of 
normal  nitric  acid  taken  to  dissolve  5  grammes  of  pure 
•copper  (266*6  c.c.)  was  purposely  taken,  so  as  to  corre- 
spond with  the  quantity  of  8  c.c.  of  normal  nitric  acid 
which  is  applied  in  the  assay  of  the  copper  obtained  from 
the  ore,  and  this  quantity  of  acid  is  exactly  met  with  in  30 
c.c.  of  the  solution  of  pure  copper. 

As  regards  No.  1  and  No.  2  (see  above),  the  influence 
of  double  quantities  of  ammonium  nitrate  and  free  caustic 
ammonia  (the  quantity  of  copper  remaining  the  same),  and 
the  action  of  dilute  solution  of  potassium  cyanide  there- 
upon, will  become  elucidated  by  the  following  facts  : — 

a.  Thirty  c.c.  of  the  normal  solution  of  copper,  con- 
taining  exactly  0-15  gramme  of  copper,  were   rendered 
alkaline  with  10  c.c.  of  normal  ammonia,  and  are  found 
to  require,  for  entire  decoloration,  29-8  c.c.  of  potassium 
cyanide  solution  ;  a  second  experiment,  again  with  30  c.c. 
of  normal  copper  solution,  and  otherwise  under  identically 
the  same  conditions,  required  29'9  c.c.  of  cyanide  solution. 
The  average  of  the  two  experiments  is  29'85  c.c. 

b.  When  to  30  c.c.  of  the  normal  copper  solution  first 
8  c.c.  of  normal  nitric  acid  are  added,  and  then  20  c.c.  of 
normal  ammonia  solution,  instead  of  only  8,  whereby  the 
quantity  of  free  ammonia   and  of  ammonium  nitrate  is 
made  double  what  it  was  in  the  case  of  the  experiments 
spoken  of  under  a,  there  is  required  of  the  same  cyanide 
solution  30-3  c.c.  to  produce  decoloration.     A  repetition 
of  the  experiment,  under  exactly  the  same  conditions,  gave 
30-4  c.c.  of  the  cyanide  solution  employed ;  the  average 
of  both  experiments  is,  therefore,  30-35  c.c. 

The  difference  between  30-35  and  2 9 -85  is  equal  to 
0-5  c.c.,  and  that  figure  is  therefore  the  coefficient  of  the 
influence  of  double  quantities  ;  and  supposing  this  to 
happen  with  the  ores  in  question,  it  would  only  be  equiva- 
lent to  0-05  per  cent,  of  metallic  copper.  It  is  hence  clear 
that  slight  aberrations  of  from  O'l  to  0-5  c.c.  in  the 
measuring  out  of  8  c.c.  of  normal  nitric  acid,  used  to 
dissolve  the  spongy  copper,  and  of  10  c.c.  of  normal 


432  THE   ASSAY   OF   COPPER. 

ammonia,  in  order  to  render  the  nitric  acid  copper  solu- 
tion alkaline,  are  of  no  consequence  whatever  for  the 
technical  results  to  be  deduced  from  the  assay ;  it  should, 
moreover,  be  borne  in  mind  that  the  quantities  of  free 
ammonia  and  of  ammonium  nitrate  in  the  actual  assay  of 
ores,  for  which  always  a  quantity  of  5  grammes  of  ore  is 
taken,  vary  according  to  the  richness  or  poverty  of  the 
ores  in  copper ;  and  the  quotation  of  the  following  results 
of  experiments  proves  that  the  influence  of  these  sub- 
stances is  only  very  slightly  felt  in  the  accuracy  of  the 
results  : — 

Eight  c.c.  of  the  normal  nitric  acid  have  been  found  to 
contain,  by  means  of  a  series  of  experiments,  1-353  gramme 
of  anhydrous  nitric  acid ;  and  this  quantity  of  acid  is 
exactly  neutralised  by  7 '7  c.c.  of  normal  ammonia  solu- 
tion, which  contains  0'6515  gramme  of  ammonium  oxide  ; 
and  10  c.c.  of  the  said  normal  solution  contain  0-846 
gramme  of  ammonium  oxide. 

One  gramme  of  metallic  copper  requires,  for  complete 
oxidation,  0-2523  gramme  of  oxygen,  and  this  quantity  of 
oxygen  is  given  off  by  0*5676  gramme  of  anhydrous  nitric 
acid  ;  while,  at  the  same  time,  binoxide  of  nitrogen  is 
disengaged.  From  these  data  can  be  calculated  (1)  the 
quantity  of  nitric  acid  which  becomes  decomposed  when 
variable  quantities  of  metallic  copper  are  dissolved 
therein  ;  (2)  what  quantity  of  nitric  acid  is  left  to  form 
neutral  nitrate  of  ammonium ;  and  (3)  what  quantity  of 
free  ammonia  will  be  left  after  a  portion  of  that  alkali  has 
been  combined  with,  and  therefore  neutralised  by,  copper 
oxide ;  and  any  remaining  free  nitric  acid. 

It  is  found  that  the  quantitative  variations  between 
ores  containing  1  per  cent,  or  6  per  cent,  of  metal  vary 
very  little  from  the  normal  quantities  exhibited  by  ores 
containing  3  per  cent,  of  metal.  The  relation  is  as  1  :  2  ; 
and,  for  technical  purposes,  this  has  been  proved  not  to 
be  a  disturbing  quantity. 

When,  however,  larger  quantities  of  ammoniacal  salts 
are  present  in  the  fluid  to  be  assayed  for  copper,  by  means 
of  a  titrated  solution  of  potassium  cyanide,  and  especially 


STEINBECK  S   PROCESS.  433 

when  ammonium  carbonate,  sulphate,  and,  worse  still, 
chloride,  are  simultaneously  present,  these  salts  exert  a 
very  disturbing  influence. 

The  presence  of  lead  oxide  in  the  copper  solution  to 
be  assayed  has  the  effect  of  producing,  on  the  addition  of 
10  c.c.  of  normal  ammonia  a  milkiness  along  with  the 
blue  tint ;  but  the  presence  of  this  oxide  does  not  at  all 
interfere  with  the  estimation  of  the  copper  by  means  of 
the  cyanide,  provided  the  lead  be  not  in  great  excess ;  and 
a  slight  milkiness  of  the  solution  even  promotes  the  visi- 
bility of  the  approaching  end  of  the  operation. 

Dr.  Steinbeck,  however,  purposely  made  some  experi- 
ments to  test  this  point,  and  his  results  show  that  neither 
50  nor  100  per  cent,  of  addition  cf  lead  exerts  any  per- 
ceptible influence  upon  the  estimation  of  copper,  from  its 
ores  or  otherwise,  by  means  of  potassium  cyanide.  A 
small  quantity  of  accidentally  occurring  lead  will  not, 
therefore,  affect  the  results,  and  this  the  less  so  as,  gener- 
ally, no  ores  of  both  metals  occur  together  wherein  both 
are  met  in  sufficient  quantity  to  make  it  worth  while 
working  the  ore  for  both  metals  at  the  same  time. 

Since  it  is  well  known  that  the  presence  of  zinc  very 
perceptibly  influences  the  action  of  a  solution  of  potassium 
cyanide,  when  applied  to  the  volunietrical  estimation  of 
copper,  Dr.  Steinbeck  considered  it  necessary  to  institute 
some  experiments  in  order  precisely  to  ascertain  with 
what  quantity  of  zinc  present  along  with  copper  this  in- 
fluence commences  to  become  perceptible.  The  solution 
of  zinc  applied  was  made  by  dissolving  the  metal  in  the 
smallest  possible  quantity  of  nitric  acid ;  and  1  c  c.  of  that 
solution  contained  0*001  gramme  of  zinc.  The  results  of 
the  experiments  show  that  the  presence  of  zinc  does  not 
interfere  with  the  visibility  of  the  end  of  the  reaction,  viz., 
the  decoloration  of  the  copper  solution.  They  also  prove 
that  a  small  quantity  of  zinc,  less  than  5  per  cent,  of  the 
quantity  of  copper  present,  or  0-0075  gramme  by  weight 
of  zinc,  does  not  at  all  affect  the  action  of  the  solution 
of  potassium  cyanide ;  but  when  the  quantity  of  zinc 
increases,  a  very  perceptible  effect  is  seen  upon  the 

F  F 


434  THE   ASSAY   OF    COPPER. 

solution  of  cyanide  ;  it  is  therefore  necessary  to  bestow 
due  care  while  washing  the  spongy  copper,  after  it  has 
been  precipitated  by  means  of  zinc  from  its  solution. 
>'  •  Since  it  has  been  ascertained  that  the  action  of  the 
solution  of  potassium  cyanide  in  researches  of  this  kind 
is  also  affected  by  an  increased  temperature  of  the  solu- 
tion of  copper  which  is  to  be  titrated,  it  is  strictly  neces- 
sary never  to  operate  with  warm  ammoniacal  solutions  of 
copper,  but  to  suffer  the  same  to  cool  down  to  the  ordinary 
temperature  of  the  air  of  the  laboratory. 

While  30  c.c.  of  copper-  solution,  containing  0-15 
gramme  of  copper,  and  10  c.c.  of  normal  ammonia  solu- 
tion, required  at  the  ordinary  temperature  30  c.c.  of 
cyanide  solution,  the  same  quantities  required,  at  between 
40°  to  45°  C.,  28-8  c.c.  of  solution  of  cyanide  ;  and  at  45° 
C.,  28*9  c.c.  of  the  same  solution,  thus  proving  the  injurious 
effect  of  warm  solutions. 

ESTIMATION  OP  COPPER  IN  THE  MANSPELD  ORES  BY  M.  C 
LUCKOW'S  PROCESS. — This  gentleman  has  applied  to  the 
quantitative  estimation  of  copper  a  new  method,  based 
upon  the  precipitation  of  the  metal  in  the  metallic  state 
from  solutions  containing  either  free  sulphuric  or  nitric 
acids,  by  means  of  a  galvanic  current. 

It  is  a  great  advantage  of  this  method,  that,  while  the 
copper  is  precipitated,  it  is  simultaneously  separated  from 
metals  with  which  it  is  often  found  alloyed  ;  some  of  these, 
such  as  tin  and  antimony,  are  separated  by  treatment  with 
nitric  acid  in  an  insoluble  form,  while  others,  like  silver, 
can  easily  be  removed  in  the  form  of  chloride.  It  is,  at 
the  same  time,  another  advantage  that  the  state  in  which 
the  copper  is  obtained  admits  of  its  being  accurately 
weighed  and  estimated,  while  a  great  number  of  opera- 
tions, which  require  much  time  and  various  apparatus,  are 
at  the  same  time  got  rid  of. 

Although  M.  Luckow  had  previously  discovered  a 
method  of  electro-metallic  analysis  from  fluids  containing 
free  sulphuric  acid,  his  researches  on  the  same  subject, 
in  the  case  of  free  nitric  acid,  belong  to  a  recent  period. 
These  researches  brought  very  unexpectedly  to  light  the 


LUCKOW'S   PROCESS.  43-5 

curious  fact  that  even  a  weak  galvanic  current  had  the 
power  of  completely  precipitating  copper  in  a  pure  metal- 
lj^  state  from  nitric  solutions,  provided  they  did  not  con- 
tain mere  than  O'l  grm.  of  anhydrous  nitric  acid  to  the 
c.c.  (nitric  acid  of  1*2  sp..  gr.  contains  0'32  grm.  of  anhy- 
drous nitric  acid  to  the  c.c.) ;  while  it  was  found  that 

•  / 

action  was,  at  the  same  time,  more  regular,  and 
dependent  upon  the  power  of  the  current  than  when  free 
sulphuric  acid  was  present.  The  following  more  commonly 
occurring  metals  are  not  precipitated  by  galvanic  action 
from  acid  solutions  : — Zinc,  iron,  nickel,  cobalt,  chromium, 
the  metals  of  the  earths  and  alkalies.  The  following  are 
precipitated  (a)  in  the  shape  of  peroxides,  at  the  positive 
electrode  :  completely,  lead  and  manganese  ;  incompletely, 
silver.  When  the  solution  contains  traces  of  manganese, 
it  becomes,  in  consequence  of  the  formation  of  a  salt  of 
manganese  peroxide,  or  of  permanganic  acid,  deeply 
violet-coloured.  This  very  sensitive  reaction  for  man- 
ganese also  takes  place  when  small  quantities  of  chlorine 
are  present.  The  presence  in  the  fluid  of  oxalic,  lactic, 
and  tartarie  acids,  and  other  readily  oxidisable  organic 
substances,  and  such  protoxides  as  are  readily  peroxidised 
— for  instance^  iron  protoxide — retards  the  formation  of 
peroxides,  as^vefl  as  the  occurrence  of  the  reaction  of 
manganese.  A 

(b)  Mercury,  silver,  copper,  and  bismuth  are  precipi- 
tated at  the  negative  electrode  in  a  metallic  state.  When 
mercury  is  present  in  the  solution  simultaneously  with 
copper,  the  former  metal  is  separated  before  the  latter,  in 
the  fluid  metallic  state.  As  soon,  however,  as  the  pre- 
cipitation of  copper  commences,  an  amalgam  of  the  two 
metals  is  formed,  when  mercury  is  also  present.  Silver  is 
precipitated  almost  simultaneously  with  copper,  bismuth 
only  begins  to  be  precipitated  after  the  greater  portion  of 
the  copper  has  been  separated.  A  complete  separation  of 
silver  only  ensues  when  some  such  substance  as  tartarie  or 
other  similar  acid  is  simultaneously  present  in  the  solution. 
The  separation  of  the  three  last-named  metals,  by  means 
of  galvanic  action,  is,  therefore,  unsuccessful ;  but,  fortu- 

p  F  2 


436  THE    ASSAY   OF    COPPER. 

nately,  there  are  many  other  means  to  accomplish  this  end 
completely. 

(c)  Metallic  arsenic  is  only  precipitated  slow]*,  and 
long  after  the  complete  separation  of  copper,  if  Qrsemc 
acid  happen  to  be  present.  The  same  remark  applies  to 
ptimony,  since  it  is  well  known  that  small  quantities  of 
Ltimonie  acid  are  soluble  in  nitric  acid.  A 

The  operations,  according  to  Luckow's  plan,  are — 1. 
Boasting  the  ore  ;  2.  Solution  of  the  roasted  product ;  3. 
Precipitation^of  the  copper  ;  4.  Weighing  the  copper. 

1.  'Roasting  the  Ore. — Care  should  be  taken  to  obtaiia 
a  finely-ground  average  sample  of  the  ore.     Then  weigh 
off  in  small  porcelain  capsules,  previously  counterpoised, 
quantities  of  from  1  to  3  grms. ;  these  quantities  ate  then 
placed  on  the  inverted  lid  of  an  iron  crucible,  on  the  inner 
surface  of  which  the  powdered  ore  is  heated  over  the  flame 
of  a  Btmsen  gas-burner.     The  powder  may  be  carefully 
stirred  up  with  a  platinum  wire,  to  promote  the  access  of     - 
air  during  the  roasting  ;  the  ignition  of  bituminous  matter  J|L 
and  sulphur  will  be  ended  in  about  seven  minutes.     OresBr 
which  do  not  contain  bitumen  at  all  need  not  be  roasted. 

It  has  been  already  stated  that  in  the  case  of  poor 
copper  ores  (and  those  of  the  Mansfeld  distiict  are  gener- 
ally so),  the  quantities  to  Ipe  weighed  off  for  assay  should 
not  vary  according  to  a  presumed  percenfige  of  copper. 
Two  grms.  are  therefore  taken,  and,  instem  of  roasting 
the  ore  on  the  lid  of  an  iron  crucible,*  small  porcelain 
crucibles  are  used  for  that  purpose. 

2.  Solution  of  the  Roasted  Product. — The  iron  lid  is 
suffered  to  cool,  the  roasted  powder  placed  on  a  piece  of 
glazed  paper,  and  any  powder  adhering  to  the  lid  is  re- 
moved by  means  of  a  camel's-hair  brush  on  to  the  paper. 
The  powder  is  next  transferred  to  small  beaker  glasses, 
and  about  2  or  3  c.c.  of  nitric  acid,  of  1*2  specific  gravity, 
are  added,  along  with  about  10  to  15  drops  of  concentrated 
sulphuric  acid.     The  beakers  are  then  placed  on  a  sand- 
bath  and  moderately  heated,  at  first ;  but  when  the  con- 
tents have  become  nearly  dr^,  the  heat  is  increased,  so  as 
to  evaporate  and  expel  all  sulphuric  acid.     The  beakers 


LUCKOW'S   PROCESS.  437 

should  be  covered  with  perforated  watch-glasses.  This 
operation  requires  from  about  three-quarters  of  an  hour 
to  on^  hour.  The  addition  of  sulphuric  acid  is  made  in 
order  ^o  increase  t'he  oxidising  action  of  the  nitric  acid , 
and  also  to  conveBk  any  lime  which  may  happen  to  be 
present  in  the  ore  ujjy  a  difficultly  soluble  salt.  It  is  very 
useful,  also,  to  add  from  10  to  20  drops  of  hydrochloric 
acid  to  th*  mixture  of  the  two  acids  just  alluded  to,  since 
the  rapidity  of  the  evaporation  is  thereby  increased,  and 
the  occasional  spirting  about  of  the  fluid  is  lessened. 

The  process  just  described  may  be  modified,  first,  by 
the  use  of  porcelain  capsules,  the  contents  of  which  are 
easily'  transferred  to  beakers  with  flat  bottoms,  and  not 
higher  than  about  2  inches  altogether.  It  is  better,  .als/), 
to  use  sulphuric  acid,  prepared  with  equal  bulKs  of  con- 
centrated acid  and  water,  and  to  measure 
off  4  <ic.  for  each  assay  ;  while  for  eacl 
assay,  moreover,  6  c.c.  of  nitric  acid 
about  25  drops  of  hydrochloric  acid  a: 
taken.  Instead  of  covering  the  beaker 
with  a  perforated  watch-glass,  th^  upper 
part  of  a  funnel  is  used,  as  represented  ^  .  , 

in  Fig.  93 ;  with  this  arrangement  the  ^fcphuric  acid 
evaporates  far  more  readily,  and  loss  by  spiting  is  pre- 
vented. The  beaker  is  heated  on  a  well- arranged  sand- 
bath. 

3.  Precipitatkn  of  the  Copper. — As  soon  as  the  beaker 
after  removal  frSn  the  sand-bath  has  became  quite  cool, 
the  funnel  which  has  been  used  as  a  cover  is  washed  on 
both  sides,  inner  and  outer,  with  nitric  acid  of  1*2  sp.  gr., 
diluted  with  six  times  its  bulk  of  pure  water  ;  the  sides  of 
the  beaker  are  next*  likewise  washed,  and  'it  is  then  filled 
to  about  half  its  height  with  the  same  acid.  A  few  drops 
of  a  concentrated  solution  of  tartaric  acid  are  added  (this 
acid  is  best  kept  in  solution  in  open  vessels,'  only  slightly 
covered  with  a  piece  of  paper) ;  this  having  been  done, 
the  wire  spiral,  represented  in  Fig.^4,  is  carefully  placed 
in  the  beaker.  This  spiral  consist^™"  a  piece  of  platinum 
wire,  about  1-1 2th  of  an  inch  thick^  and  7^  inches  long, 


438 


THE   ASSAY   OF   COPPER. 


two-thirds  of  its  length  being  so  wound  fliat  the  straight 
end  of  the  wire  projects  as  if  it  were  the  axis  of  the  centre 
of  the  spiral.  The  convolutions  of  the  spiral  are  so  large 
that  they  touch  the  sides  of  the  beaker,' while  the  straight 
portion  just  touches  the  centre  of  the/bottom  of  the  vessel. 
When  the  heating  has  been  c^jcfully  attended  to, 
the  acid  fluid  added  to  the  contents  of  the  beaker,  after 
evaporation  to  dry  ness,  will  generally  be  quite  -^clear  ;  if  it 
happens  to  be  turbid,  1  or  2  c.c.  of  a  concentrated  solution 
of  barium  nitrate  may  be  added,  and  the  thorough  mixing 
of  this  saline  solution  with  the  acid  contents  of  the  beaker 


FIG.  94. 


FIG.  95. 


promoted  by  gently  moving  up  and  down  the  platinum 
spiral  just  alluded  to,  and  allowing  the  fluid  to  rest  for  a 
few  minutes  after.  The  copper  present  in  the  mass  left  at 
the  bottom  of  the  beaker  gradually  dissolves,  and  it  is  not 
actually  requisite  to  wait  before  applying  the  galvanic 
current  until  it  is  all  dissolved. 

The  next  point  is  to  place  in  the  beaker  the  platinum 
foil,  represented  at  Fig.  95,  of  which  the  dimensions  are  — 


length,  2;L  inches  ; 


inch.     Tl/e  lower  end  of  this 


platinum  foil  should    e  kept  about  1-1  6th  of  an  inch  apart 
from  the  convolutions  of  the  spiral.     When  the  beaker  is 


LUCKOW  S   PROCESS.  439 

only  half  filled  with  liquid,  the  platinum  foil  is  immersed 
in  the  same  for  more  than  three-fourths  of  its  height.  The 
wire  fastened  'to  this  foil  is  fixed,  by  means  of  a  screw,  a, 
to  the  arm,  a,  &,  of  the  stand,  represented  in  Fig.  96  ;  the 
other  screw,  b,  serves  to  fasten  a  copper  wire,  proceeding 
from  the  zinc  end  of  the  galvanic  battery.  When  the 
small  screw  clamp,  c  (Fig.  96),  has  been  fastened  to  the 
platinum  wire  placed  in  the  beaker,  another  wire  is 
fastened  in  the  top  opening  of  the  clamp,  and  this  wire 
connected  with  the  copper  end  of  the  battery,  and  the 
galvanic  circuit  thus  closed.  In  a  few  moments  after  this  ' 
has  been  done,  the  platinum  foil,  bent  in  the  shape  of  the 
cylinder  and  placed  inside  the  beaker,  as  before  described, 
will  be  observed  to  become  covered  with  a  coating  of 
metallic  copper,  while  from  the  platinum  wire  spiral 
bubbles  of  gas  escape,  which  facilitate,  to  some  extent,  the 
solution  of  the  copper  oxide  in  the  dilute  acid. 

In  order  to  ascertain  whether  the  whole  quantity  of 
the  copper  has  been  precipitated,  some  more  dilute  nitric 
acid  is  added  to  the  fluid  in  the  beaker  glass.  If,  in  ten 
minutes  after  this,  no  more  metallic  copper  is  separated  on 
the  clean  portions  of  the  platinum  foil,  the  operation  is 
finished. 

It  must  be  here  observed  that  continued  practice  has 
proved  that  the  addition  of  a  concentrated  solution  of 
barium  nitrate  acts  injuriously  on  the  process,  as  the 
metallic  copper,  which  becomes  separated,  gets  mixed 
with  some  insoluble  barium  sulphate,  which  increases  the 
weight  of  the  substance  to  be  weighed. 

The  time  occupied  by  the  complete  precipitation  of  the 
metal  varies  according  to  the  force  of  the  galvanic  current. 
It  takes  from  three  to  even  eight  hours.  In  order  to  make 
this  point  certain,  all  test  assays  are  left,  for  eight  hours 
consecutively,  to  the  action  of  the  galvanic  current,  expe- 
rience having  proved  that,  after  that  lapse  of  time,  even 
with  a  weak  current,  the  precipitation  was  so  complete 
that  all  chemical  reagents  for  detecting  the  presence  of 
copper  failed  to  discover  the  most  minute  trace  of  that 
metal. 


440  THE   ASSAY    OF   COPPER. 

4.  Weighing  the  Copper. — The  platinum  cylinder  to 
which  the  copper  adheres,  and  the  platinum  wire  spiral, 
are  disconnected  from  the  galvanic  apparatus,  the  plati- 
num cylinder  carefully  removed  from  the  beaker  and 
immediately  plunged  into  a  beaker  filled  with  fresh  cold 
water,  and  rinsed  therein  ;  next  washed  with  alcohol,  by 
means  of  a  washing  bottle,  and  then  dried  in  a  drying  ap- 
paratus, and  weighed  after  cooling.  Since  the  platinum 
cylinder  has  been  very  accurately  weighed  before  the 
experiment,  its  increase  in  weight  will,  of  course,  be  that 
of  the  copper  obtained. 

The  process  here  described  has  been  somewhat  modi- 
fied and  greatly  improved  upon  at  Eisleben,  where  it  is  in 
constant  use,  by  the  employment  >of  a  series  of  galvanic 
elements.  It  is,  in  the  first  place,  found  better  not  to 
disconnect  the  galvanic  current  while  the  copper  is  yet  in 
contact  with  acid,  so  that,  instead  thereof,  the  acid  fluid  in 
the  beaker  is  replaced  by  turning  in  a  stream  of  water, 
and  suffering  the  same  to  run  over  the  sides  of  the  beaker, 
and  to  be  received  into  a  proper  vessel  to  hold  it.  In 
this  manner  all  the  acid  is  displaced,  without  risk  of 
any  very  small  quantity  of  copper  becoming  acted  upon 
by  the  acid  during  the  brief  period  elapsing  between  the 
disconnecting  of  the  galvanic  current  and  the  removal 
from  the  beaker  of  the  platinum  cylinder  and  spiral  wire. 
These  parts,  on  being  removed,  are  carefully  washed,  first 
with  boiling  water,  next  with  alcohol,  and  then  dried  at  a 
temperature  of  about  the  boiling  point  of  water.  The 
cylinder  is  then  weighed,  the  copper  coating  is  removed 
by  means  of  nitric  acid  ;  the  platinum  is  next  washed  in 
water,  dried,  and  again  weighed. 

There  are  in  use  at  Eisleben  nine  galvanic  batteries 
(lead  and  zinc  elements) ;  these  yield  eighteen  assays  ready 
for  weighing  in  twenty-four  hours  ;  and  it  would  not  be 
difficult  for  the  person  there  employed  to  work  with  twelve 
batteries  each  of  three  elements.  In  place  of  the  Mei- 
dinger  elements,  which  do  not  remain  constant  for  months, 
a  thermo-electric  apparatus  has  been  introduced,  with  the 
best  results.  The  results  obtained  are  highly  satisfactory. 


BLOWPIPE   DETECTION   OF   COPPER.  441 

The  following  observations  may  be  made  in  reference  to 
this  method : — 

(a)  The  quantity  of  ore  taken  for  trial  is  2  grammes  ; 
this  is  found  sufficient,  while  it  consumes  less  acid. 

(b)  The  evaporation  of  the  acid  is  carried  on  to  com- 
plete dryness  on  the  sand-bath.     Spirting  of  the  fluid  is 
easily  prevented. 

When  the  copper  has  been  precipitated  properly  it 
will  show  its  peculiar  colour  on  the  surface,  and  the  good 
success  of  the  operation  may  also  be  judged  from  the  fact 
that  no  saline  matter  adheres  to  the  platinum  ;  the  com- 
plete absence  of  this  saline  matter  has  been  found  to 
be  evidence  of  perfect  removal  of  the  copper  from  the 
fluid. 

The  process  just  described  is  especially  applicable  for 
rather  poor  ores,  such  as  do  not  contain  above  7  or  8  per 
cent,  of  copper.  Each  assay,  from  beginning  to  end,  takes 
ten  hours  for  complete  analysis ;  but  it  is  evident  that  the 
greater  portion  of  this  period  does  not  give  active  employ- 
ment to  the  assayer.  The  expense  of  working  this  process, 
after  the  apparatus  has  been  once  purchased,  is  very  small. 
The  process  may  also  be  applied  to  analyse  richer  ores, 
and  also  alloys  of  copper,  with  some  slight  modifications 
which  will  readily  suggest  themselves. 

Professor  Chapman,  of  Toronto,  gives  the  following 
directions  for  the  detection  of  minute  traces  of  copper  in 
iron  pyrites  and  other  bodies  :  — 

s  Although  an  exceedingly  small  percentage  of  copper 
may  be  detected  in  blowpipe  experiments  by  the  reducing 
process  as  well  as  by  the  azure  blue  colouration  of  the 
flame,  when  the  test  matter  is  moistened  with  hydrochloric 
acid,  these  methods  fail  in  certain  extreme  cases  to  give 
satisfactory  results.  It  often  happens  that  veins  of  iron 
pyrites  lead  at  greater  depths  to  copper  pyrites.  In  this  case, 
according  to  the  experience  of  the  writer,  the  iron  pyrites 
will  almost  invariably  hold  minute  traces  of  copper.  Hence 
the  desirability,  on  exploring  expeditions  more  especially, 
of  some  ready  test  by  which,  without  the  necessity  of 
employing  acids  or  other  bulky  and  difficultly  portable 


442  THE   ASSAY   OF   COPPER. 

reagents,  these  traces  of  copper  maybe  detected.*  The  fol- 
lowing simple  method  will  be  found  to  answer  the  pur- 
pose : — The  test  substance,  in  powder,  must  first  be  roasted 
on  charcoal,  or,  better,  on  a  fragment  of  porcelain,f  in 
order  to  drive  off  the  sulphur.  A  small  portion  of  the 
roasted  ore  is  then  to  be  fused  on  platinum  wire  with 
phosphor-salt ;  and  some  potassium  bisulphate  is  to  be 
added  to  the  glass  (without  this  being  removed  from  the 
wire)  in  two  or  three  successive  portions,  or  until  the  glass 
becomes  more  or  less  saturated.  This  effected,  the  bead 
is  to  be  shaken  off  the  platinum  loop  into  a  small  capsule, 
and  treated  with  boiling  water,  by  which  either  the  whole 
or  the  greater  part  will  be  dissolved  ;  and  the  solution  is 
finally  to  be  tested  with  a  small  fragment  of  potassium 
ferrocyanide.  If  copper  be  present  in  more  than  traces, 
this  reagent,  it  is  well  known,  will  produce  a  deep  red  pre- 
cipitate. If  the  copper  be  present  in  smaller  quantity — 
that  is,  in  exceedingly  minute  traces — the  precipitate  will 
be  brown  or  brownish-black ;  and  if  copper  be  entirely 
absent,  the  precipitate  will  be  blue  or  green — assuming,  of 
course,  that  iron  pyrites  or  some  other  ferruginous  sub- 
stance is  operated  upon.  In  this  experiment  the  prelimi- 
nary fusion  with  phosphor-salt  greatly  facilitates  the  after 
solution  of  the  substance  in  potassium  bisulphate.  In 
some  instances,  indeed,  no  solution  takes  place  if  this  pre- 
liminary treatment  with  phosphor-salt  be  omitted. 

Mr.  J.  M.  Merrick  has  published  in  the  '  Chemical 
News  '  a  gravimetric  method  which  has  led  to  trustworthy 
results,  even  when  the  amount  of  copper  present  was  very 
much  less  than  half  a  milligramme. 

*  In  blowpipe  practice — as  far,  at  least,  as  this  is  possible — the  operator 
should  make  it  an  essential  aim  to  render  himself  independent  of  the  use  of 
mineral  acids  and  other  liquid  and  inconvenient  reagents  of  a  similar  character. 
If  these  reagents  cannot  be  dispensed  with  altogether,  their  use,  by  improved 
processes,  may  be  greatly  limited. 

t  In  the  roasting  of  metallic  sulphides,  &c.,  the  writer  has  employed,  for 
some  years,  small  fragments  of  Berlin  or  Meissen  porcelain,  such  as  result  from 
the  breakage  of  crucibles  and  other  vessels  of  that  material.  The  test  sub- 
stance is  crushed  to  powder,  moistened  slightly,  and  spread  over  the  surface  of 
the  porcelain  ;  and  when  the  operation  is  finished,  the  powder  is  easily  scraped 
off  by  the  point  of  a  knife-blade  or  small  steel  spatula.  In  roasting  operations, 
rarely  more  than  a  dull  red  heat  is  required ;  but  these  porcelain  fragments  may 
be  rendered  white-hot,  if  such  be  necessary,  without  risk  of  fracture. 


BLOWPIPE    DETECTION    OF   COPPER.  443 

It  consists  simply  in  concentrating  to  a  very  small  bulk 
the  solution  suspected  to  contain  copper,  and  then  deposit- 
ing the  copper,  if  present,  upon  platinum,  by  the  battery. 
He  uses  for  a  depositing  cell  a  very  small  test-tube,  on  a 
foot,  cut  off  so  as  to  give  a  vessel  about  1|  inches  deep. 
Into  this  is  introduced  the  solution  acidified  with  sulphuric 
acid,  and  a  platinum  anode  and  cathode — each  about  1 
inch  long,  and  -|th  of  an  inch  or  less  wide — are  hung  face 
to  face,  and  very  close  together,  and  the  circuit  being 
completed,  very  satisfactory  depositions  of  copper  are  ob- 
tained with  incredibly  minute  quantities  of  the  metal.  The 
amounts  are  determined  by  the  increased  weight  of  the 
cathode  (which  is  provided  with  a  platinum  wire  soldered 
on  with  gold,  by  which  it  is  conveniently  hooked  on  to  the 
balance),  and  by  the  loss  in  weight  of  the  same  on  washing 
it  with  nitric  acid.  The  platinum  must  be  polished  and 
heated  red-hot  before  the  first  weighing,  and  then  gently 
heated  before  hanging  in  the  solution.  The  contrast  in 
colour  between  the  deposited  copper  and  bright  platinum 
is,  of  course,  striking  and  characteristic.  In  this  way 
the  weight  of  a  milligramme  of  copper  may  be  safely 
determined,  while  for  mere  qualitative  analysis  this  method 
may  be  employed  where  the  amount  is  even  smaller. 


444 


CHAPTEE  XI. 

THE     ASSAY     OF     LEAD. 

ALL  minerals  and  substances  containing  lead  may,  for  the 
purposes  of  the  assayer  by  the  dry  way,  be  divided  into 
four  classes  : — 

Class  I.  comprises  sulphides,  antimonial  or  otherwise 
(galena,  &c.). 

Class  II.  includes  all  plumbiferous  substances  contain- 
ing neither  sulphur  nor  arsenic,  or  mere  traces  only  of 
these  elements  (litharge,  minium,  lead  carbonate,  native 
and  artificial,  lead  fume,  cupel  bottoms,  furnace  hearths, 
lead  slag,  &c.). 

Class  III.  comprises  all  substances  into  whose  com- 
position either  sulphuric,  arsenic,  chromic,  or  phosphoric 
acid,  or  a  mixture  of  either,  enters  (pyromorphite,  wolfra- 
mite, &c.). 

Class  IV.  Alloys  of  lead. 

CLASS   I. 

Before  describing  the  different  modes  of  assaying  sub- 
stances of  this  class,  it  will  be  as  well  to  pass  in  review  the 
action  of  various  reagents  on  sulphides  of  lead,  in  order 
that  the  rationale  of  the  assay  of  those  ores  may  be  better 
appreciated. 

Action  of  Oxygen. — If  galena  be  roasted  at  a  very 
gentle  temperature,  care  being  taken  to  avoid  fusion,  it 
will  be  converted  into  a  mixture  of  lead  oxide  and  lead 
sulphate,  with  evolution  of  sulphurous  acid,  thus  : — 

2(PbS)  +  70=PbO  +  PbO,S03-fS02. 
Action  of  Metallic  Iron. — This  metal  completely   and 


ALKALIES   AND   ALKALINE   CARBONATES.  445 

readily  decomposes  lead  sulphide,  giving  metallic  lead  in 
a  pure  state,  thus  : — 

PbS  +  Fe=PtH  FeS. 

On  the  one  side  we  have  lead  sulphide  and  metallic  iron, 
on  the  other  metallic  lead  and  iron  sulphide. 

The  Alkalies  and  Alkaline  Carbonates  decompose  lead 
sulphide,  but  only  partially ;  pure  lead  is  separated,  and 
at  the  same  time  a  very  fusible  grey  slag  is  formed,  which 
contains  an  alkaline  sulphate  and  a  compound  of  lead  sul- 
phide and  an  alkaline  sulphide.  A  certain  proportion  of 
the  alkali  is  reduced  by  the  sulphur,  which  is  converted 
into  sulphuric  acid,  so  that  no  lead  oxide  is  produced. 
This  reaction  may  be  thus  expressed  : — 

7(PbS)  +  4(K20)  =  4Pb  +  K20,S03  +  3(PbS,K2S). 

Potassium  Nitrate  completely  decomposes  lead  sulphide, 
with  the  reduction  of  metallic  lead  and  formation  of 
potassium  sulphate  and  sulphurous  acid,  thus  : — 

2(PbS)  +  K20,N05 = 2Pb  +  K20,S03  +  S02  +  N. 

If  the  nitre  be  in  excess,  the  lead  will  be  oxidised  in  pro- 
portion to  the  excess  present,  and  if  there  be  a  sufficiency 
added,  no  metallic  lead  at  all  will  be  produced. 

Argol. — The  presence  of  carbonaceous  matter  much 
favours  the  decomposition  of  galena,  by  determining  the 
reduction  of  a  larger  quantity  of  potassium  to  the  metallic 
state,  and  thereby  the  formation  of  a  larger  quantity  of 
alkaline  sulphide.  With  4  parts  of  argol  to  1  part  of  sul- 
phide, 80  parts  of  lead  are  reduced.  If  the  reaction  were 
complete,  the  decomposition  would  be  as  follows  : — 

PbS  +  K20 -f  C = Pb -f  K2S  +  CO. 

For  the  reactions  of  lead  oxide  (litharge)  and  lead  sul- 
phate on  sulphide  of  lead,  see  pages  186  and  188. 

From  the  reactions  above  given,  it  will  be  seen  that 
there  are  many  substances  capable  of  completely  reducing 
the  lead  from  -its  sulphide,  and  yet  few  can  be  used  safely 


446  THE   ASSAY    OF   LEAD. 

with  any  advantage,  as  so  to  use  them  would  imply  a 
knowledge  of  how  much  sulphur  and  lead  were  in  the  ore 
to  be  assayed,  in  order  to  tell  the  precise  quantity  of  either 
of  the  reagents  required  ;  for  it  is  evident  that  if  either 
more  or  less  of  some  were  added,  a  faulty  result  would  be 
the  consequence :  so  that  some  systematic  mode  of  assay, 
which  may  be  suitable  for  all  classes  of  galena,  whether 
mixed  with  other  sulphides  or  with  gangue,  must  be 
contrived.  To  facilitate  this*  we  now  proceed  to  give  an 
outline  of  the  processes  generally  adopted  in  the  assay  of 
lead  ores  by  various  persons. 

1.    FUSION   WITH    POTASSIUM    CARBONATE. 

This  plan  is  used  at  the  Oberhartz,  and  described  by 
Kerl  as  follows  : — 

One  centner  of  the  very  finely  pulverised  assay  sub- 
stance is  weighed  out,  mixed  with  three  to  four  times  its 
weight  of  pure,  dry,  and,  finely  pulverised  potassium  car- 
bonate, and  covered  over,  in  a  small  clay  crucible  (fig.  61), 
with  a  layer  of  decrepitated  sodium  chloride  about  one- 
fourth  of  an  inch  thick.  The  assays  thus  prepared  are 
placed  in  the  thoroughly  heated  muffle  of  a  large  assay 
furnace  (figs.  23,  24)  having  a  strong  draught.  They  re- 
main in  the  highest  temperature  of  the  furnace,  with  the 
mouth  of  the  muffle  closed  with  glowing  coals,  till  they 
have  come  into  perfect  fusion  (about  twenty  to  thirty 
minutes).  The  draught  opening  is  then  closed,  and  at  the 
same  time  the  muffle  opened,  until  the  temperature  has 
fallen  so  far  that  the  crucibles  appear  brownish-red,  and 
the  vapours  above  them  have  greatly  diminished,  or  have 
disappeared.  At  this  heat  the  crucibles — whose  contents 
must,  however,  always  remain  in  perfect  fusion — are  main- 
tained, according  to  the  fusibility  and  composition  of  the 
assay  sample,  and  the  draught  of  the  furnace  for  a  longer 
or  shorter  time  (ten  to  twenty-five,  generally  ten  minutes). 
This  period  during  which  the  heat  is  allowed  to  remain 
low,  is  called  the  cooling  of  the  assay. 

The  furnace  is  now   again  brought  back   to  its  first 


FUSION   WITH    CARBONATE    OF   POTASH.  447 

temperature,  by  completely  opening  the  draught  and'  ' 
closing  the  muffle.  Ten  to  fifteen  minutes  of  this  last  heat- 
ing are  in  most  cases  sufficient.  Only  poor  ores,  &c.,  which 
contain  also  a  pretty  large  quantity  of  arsenic,  or  of  iron, 
zinc,  and  copper  sulphides,  are  allowed  to  continue  hot 
five  to  ten  minutes  longer. 

If  many  assays  are  to  be  made,  it  will  be  found  advan- 
tageous to  mix  those  which  contain  larger  quantities  of 
foreign  sulphides,  or,  by  reason  of  their  earthy  contents, 
are  difficultly  fusible,  with  more  or  less  borax ;  or,  instead 
of  this,  to  place  them  in  the  back  and  hotter  part  of  the 
muffle,  while  those  that  are  very  rich  in  lead  and  easily 
fusible  are  placed  in  front,  since  the  latter  will  be  hot 
enough  here,  and  more  easily  reached  by  the  air  than 
those  deeper  in  the  muffle. 

The  crucibles,  when  cold,  are  broken,  the  -lead  buttons 
obtained  are  freed  from  all  adhering  slag  or  substance  of 
the  crucible,  and  if  the  assay  were  otherwise  successful, 
their  weight  determined.  The  assays  should  not  be  too 
rapidly  cooled,  because  the  slag  is  thus  easily  cracked,  and 
the  still  half-fluid  button  lying  below  is  apt  to  be  broken 
into  several  pieces. 

In  a  successful  assay,  the  lead  melted  together  to  a 
button  deports  itself  under  the  hammer  and  knife  like  pure 
lead,  and  possesses  also  its  colour.  If  the  slag  shows,  upon 
its  surface  of  separation  from  the  metallic  button,  lead 
grey  spots  with  metallic  lustre,  it  will  generallv  also  be 
found  that  a  thin  layer  of  not  completely  decomposed 
glistening  lead  sulphide  or  subsulphide  has  at  the  same 
time  deposited  itself  upon  the  button.  This  layer,  if  the 
above  appearance  presents  itself  in  a  high  degree,  can  be 
rubbed  off  or  removed  in  fine  scales.  The  lead  button 
itself  then  shows  upon  its  surface  a  high  metallic  lustre, 
which  does  not  have  the  colour  of  pure  lead,  but  a  darker 
and  blackish  hue.  Assays  of  this  kind  are  to  be  rejected  ; 
they  have  not  been  allowed  to  remain  cool  long  enough, 
or  they  have  in  the  process  become  too  cold ;  they  give 
the  amount  of  lead  too  low,  and  often  very  considerably 
so.  In  assays  which  have  stood  too  long  in  the  furnace 


448  THE    ASSAY    OF    LEAD. 

in  the  last  fusing  heat,  a  very  bright  button  of  lead  is  also 
found  ;  but  here  the  layer  of  undecomposed  lead  sulphide 
is  wanting,  as  also  the  glistening  spots  on  the  surface  of 
the  slag  surrounding  the  button.  If  the  influence  of  the 
heat  and  air  continues  too  long,  then,  besides  a  loss  through 
volatilisation  of  the  lead,  a  slagging  of  the  lead  oxide  may 
take  place.  A  button  that  is  brittle,  laminated,  and  bril- 
liantly white  in  the  fracture,  indicates  an  insufficiency  of 
flux,  or  the  presence  of  antimony  and  arsenic.  In  successful 
assays  the  lead  button  generally  has  a  bluish  appearance 
which,  although  not  dull,  is  at  the  same  time  not  strongly 
brilliant.  The  slag  must  be  completely  homogeneous,  and 
must  have  settled  down  uniformly  towards  the  bottom  of 
the  crucible,  so  that  it  does  not  stick  in  a  thick  layer  to 
the  upper  part  of  the  sides  of  the  crucible.  It  shows  by 
this  that  it  has  been  in  proper  fusion.  It  must  have 
covered  over  the  button  in  a  thick  layer  (about  one-fourth 
of  an  inch  thick).  The  sodium  chloride  covering,  or  a 
more  or  less  colourless  slag  that  is  formed  containing 
sodium  chloride  and  potassium  carbonate,  overlies  in  a 
still  thicker  layer  the  true  dark-coloured  slag  containing 
the  foreign  metallic  oxides.  A  porous  slag  containing 
metallic  globules  indicates  a  small  quantity  of  flux  or  too 
low  a  temperature ;  a  brilliant  vitreous  slag,  too  high  a 
temperature  and  a  slagging  of  lead.  An  assay  and  its 
"duplicate  must,  moreover,  give  equal  results. 

Lead  matt  and  lead  fume  are  smelted,  with  the  addi- 
tion of  borax  and  coal-dust,  with  potassium  carbonate,  and 
with  the  first  the  heat  is  allowed  to  last  somewhat  longer 
(perhaps  to  three-quarters  of  an  hour)  than  with  ores. 
The  potassium  carbonate  assay  gives  for  lead  matt,  with  its 
not  inconsiderable  lead  contents  (30  per  cent,  and  over), 
pretty  satisfactory  results. 

The  theory  of  this  lead  assay  appears  from  the  fol- 
lowing. 

If  perfectly  pure  galena  is  intimately  mixed  with  three 
or  four  times  its  weight  of  good  dry  potassium  carbonate, 
placed  in  a  clay  retort,  and  this  so  arranged  in  the  muffle 
of  the  assay  furnace  that  its  neck  projects  from  the  mouth 


FUSION   WITH    POTASSIUM    CARBONATE.  449 

of  the  muffle,  while  in  the  opening  of  the  neck  a  glass  tube 
is  closely  fitted,  which  goes  into  a  receiver,  from  which  it 
is  further  prolonged  in  a  second  tube,  it  will  be  observed 
that  at  first  only  a  little  water  collects  in  the  receiver,  pro- 
ceeding from  the  small  quantity  of  moisture  always  present 
in  the  potassium  carbonate.  Later,  with  an  incipient  red 
heat  in  the  retort,  a  gas  is  disengaged,  which  upon  closer 
investigation  proves  to  be  pure  carbonic  acid  gas,  i.e.  free 
from  sulphurous  acid.  The  disengagement  of  gas  becomes 
more  active  with  a  stronger  red  heat,  without  yielding 
gases  of  different  composition,  but  ceases  again  after  a 
while.  In  order  to  obtain  assurance  of  a  complete  decom- 
position, the  retort  may  be  kept  for  an  hour  at  a  very 
strong  red  heat.  After  the  cooling  and  breaking  of  the 
retort,  some  pure  lead  oxide  and  carbonate  is  found 
deposited  in  the  neck  of  it,  then  a  pure  lead  button  upon 
the  bottom,  and  over  this  a  brown  slag,  free  from  little 
globules  of  lead.  It  consists  in  by  far  the  greatest  part 
of  potassium  sulphide  and  still  undecomposed  potassium  car- 
bonate, but  also  in  small  part  of  potassium  silicate  derived 
from  the  silica  of  the  retort.  If  this  slag  is  treated  with 
water  till  nothing  further  will  dissolve,  the  substances 
named  can  be  easily  shown  to  exist  in  the  solution.  The 
solution  is  colourless,  and  when  supersaturated  with  acids 
disengages  sulphuretted  hydrogen,  but  throws  down  no 
sulphur.  In  the  treatment  of  the  slag  with  water,  lead' 
sulphide  remains  behind  in  black  flocks,  even  the  exterior 
character  of  which  shows  that  it  is  not  undecomposed 
galena,  but  lead  sulphide  separated  from  a  chemical  com- 
bination. 

If  the  brown  slag  from  the  retort  is  placed  in  a  small 
uncovered  crucible  and  brought  back  into  the  hot  muffle 
of  the  assay  furnace  and  melted,  then  after  some  time, 
whether  the  slag  was  covered  with  sodium  chloride  or  not, 
a  button  of  lead  again  separates  at  the  bottom  of  the  cru- 
cible, and  the  brown  slag  now  shows  itself  decolorised. 
If  the  crucible  is  removed  from  the  furnace  too  soon, 
only  the  upper  layer  of  slag  is  decolorised,  and  that  lying 
below  is  still  completely  unchanged.  The  decolorised  slag ' 

G  G 


450  THE    ASSAY    OF    LEAD. 

consists  of  potassium  carbonate  and  sulphate,  and  no 
longer  contains  any  trace  of  potassium  sulphide. 

In  the  above-described  lead  assay,  the  process  in  the 
strong  preliminary  heat  proceeds  as  in  the  retort,  i.e.  the 
potash  of  the  potassium  carbonate  is  reduced  to  potassium, 
while  it  yields  its  oxygen  to  the  sulphur  of  the  galena  and 
with  it  forms  sulphuric  acid  ;  the  liberated  potassium  takes 
up  sulphur  from  another  portion  of  galena,  forming  potas- 
sium sulphide.  The  galena  would  now  in  this  double  way 
soon  lose  all  its  sulphur,  if  a  combination— a  sulphur  salt 
— of  potassium  sulphide  with  lead  sulphide  did  not  form, 
which  resists  all  further  action  of  the  potassium  carbonate 
[4  (K20,C02)  +  7PbS  =  4Pb  +  3  (K2S,PbS)  4  K20,S03  +  400J. 
The  carbonic  acid  of  the  thus  decomposed  potassium  car- 
bonate escapes  together  with  that  set  free  by  the  sulphuric 
acid  formed,  and  causes  a  puffing  up  of  the  mass,  by 
which  globules  of  lead  already  separated  are  raised  up 
with  it,  and  may  perhaps  remain  with  some  of  the  slag 
sticking  to  the  upper  crucible  walls.  They  would  here 
oxidise  and  produce  yellow  spots.  The  covering  of  sodium 
chloride  is  designed  to  guard  against  loss  of  lead  in  this 
and  similar  ways.  It  serves  in  a  certain  manner  to  rinse 
clown  the  sides  of  the  crucible. 

The  atmospheric  oxygen,  in  the  open  crucible,  is  not 
entirely  excluded  by  the  covering  of  sodium  chloride.  In 
the  cooling  of  the  assay,  it  oxidises  the  sulphur  salt  con- 
tained in  the  upper  part  of  the  slag,  forming  potassium 
sulphate  and  a  portion  of  lead  sulphate.  The  latter, 
during  the  last  high  heat,  decomposes  the  lead  sulphide 
still  remaining  in  the  slag,  in  such  a  way  as  to  produce 
metallic  lead.  (PbS  +  PbO,S03= 2Pb  +  2S02.)  The  reduced 
particles  of  lead  separate  well  from  the  slag  thus  rendered 
thinly  fluid.  Matts  must  be  allowed  to  cool  longer  than 
ores. 

The  potassium  carbonate  assay  presupposes  in  general 
great  practice  and  close  attention  on  the  part  of  the 
assayer ;  and  moreover,  if  one  wishes  to  find  the  correct 
value  at  once,  without  fruitless  preliminary  examinations, 
and  without  the  necessity  of  repeating  the  assay,  a  general 


FUSION   WITH    POTASSIUM    CARBONATE.  451 

knowledge  of  the  constituents  of  the  assay  sample,  so  far, 
for  example,  as  this  can  be  obtained  by  the  aid  of  minera- 
logy, is  necessary.  The  assay  after  this  method,  which 
requires  but  little  preparation,  can  only  be  conducted  in 
the  muffle  furnace,  but  then  in  pretty  large  number  (as 
many  as  fifty  at  once).  For  its  success  it  is  indispensably 
necessary  that  the  cooling  of  the  assay  be  allowed  and 
stopped  again  at  the  right  time  and  in  the  proper  degree. 
If  it  is  allowed  to  cool  too  long,  too  much  sulphate  of  lead 
is  formed  in  proportion  to  the  lead  sulphide  still  present 
in  the  slag,  and  in  the  last  heating  up,  by  the  action  of 
the  two  upon  each  other,  easily  scorifiable  oxide  of  lead  is 
produced.  (PbS  +  3PbO,S03 = 4PbO  +  4S02.)  If  the  cooling 
is  too  soon  interrupted,  only  a  small  part  of  the  lead  sul- 
phide in  the  sulphur  salt  is  oxidised,  and  by  the  action  of 
the  oxidised  portion  upon  the  lead  sulphide,  lead  sub- 
sulphide  is  produced,  which  either  remains  in  the  slag  or 
settles  upon  the  lead  button.  (2PbS  +  PbQ,S03=Pb2S  +  2Pb 
-f  2S02.)  Experience  gives  the  only  means  at  hand  to 
guide  us  here,  but  leaves  us  easily  in  the  lurch,  so  that 
the  result  of  the  assay  becomes  more  doubtful  than  in 
some  of  the  methods  hereafter  described. 

With  substances  containing  antimony  this  assay  deserves 
the  preference  over  the  others,  since  most  of  the  antimony 
remains  in  the  slag  in  the  state  of  sulphide  and  oxide.  An 
addition  of  saltpetre  works  advantageously.  Arsenic  and 
arsenic  sulphide  mostly  go  off  in  fumes  during  the  smelt- 
ing, but  nevertheless  always  cause  the  formation  of  a 
brittle  metallic  button.  Copper  sulphide  remains  in  great 
part  in  the  slag,  but  a  part  of  the  copper  is  desulphurised 
and  goes  into  the  lead.  If  the  quantity  of  copper  present 
is  very  considerable,  the  button  of  metal  may  be  considered 
as  black  copper,  and  refined,  and  the  loss  thereby  occur- 
ring, reckoned  as  lead. 

Iron  protosidphide,  which  occurs,  for  example,  in  lead 
matt,  is  decomposed  by  potassium  carbonate,  forming 
metallic  iron,  which  desulphurises  the  galena.  Iron  pyrites, 
on  the  other  hand,  occasions  the  forming  of  a  large  quan- 

G  G  2 


452  THE   ASSAY    OF    LEAD. 

tity  of  potassium  sulphide  and,  in  consequence  of  this,  of 
a  sulphur  salt. 

It  follows,  therefore,  from  the  above,  that  ores  which 
contain  much  foreign  sulphides  are  not  suited  to  this 
method  of  assaying,  since  they  cause  the  production  of  a 
large  amount  of  potassium  sulphide,  which  always  retains 
lead  sulphide.  By  an  addition  of  saltpetre  to  the  potas- 
sium carbonate,  these  sulphides  may,  indeed,  be  partially 
decomposed  :  only  an  oxidation  of  the  lead  is  apt  to  be 
produced,  as  well  as  a  mechanical  loss  by  the  violent 
action  of  the  saltpetre. 

From  pure  galena,  by  the  potassium  carbonate  assay, 
80  per  cent,  of  lead  at  most  can  be  obtained.  Calcined 
sodium  carbonate  is  inferior  to  potassium  carbonate  as  a 
desulphurising  agent,  and  always  yields  a  few  per  cent, 
less  lead  than  the  latter.  According  to  Phillips,  75  to  77 
per  cent,  of  lead  is  obtained  from  galena  with  sodium  car- 
bonate. With  potassium  cyanide,  under  certain  circum- 
stances, the  same  result  can  be  obtained  as  with  potassium 
carbonate,  and  it  does  not  require  so  high  nor  so  long 
continued  a  temperature ;  still  it  offers  no  real  advantage 
over  potassium  carbonate.  An  -addition  of  30  to  35  per 
cent,  of  saltpetre  to  an  assay,  with  which  ten  parts  of 
sodium  carbonate  are  used,  promotes,  indeed,  the  desul- 
phurising of  the  lead,  but  also  increases  the  loss  of  lead. 

At  the  Oberhartz  smelting-house,  the  lead  button  is 
weighed  out  to  pounds,  and  a  difference  of  five  pounds  is 
allowed  between  different  assayers.  It  is  also  a  custom, 
though  not  a  correct  one,  to  allow  as  many  pounds  diffe- 
rence as  there  are  tens  of  pounds  in  the  weight  of  the  lead 
button  obtained.  Thus,  with  a  lead  contents  of  thirty  and 
seventy  pounds,  the  difference  in  the  separate  assays 
might  amount  to  three  and  seven  pounds  respectively. 

2.     FUSION   WITH    BLACK   FLUX. 

A  modification  of  the  preceding  method  of  assaying, 
which  is  sometimes  employed,  consists  in  using,  instead  of 
the  potassium  carbonate,  an  equal  quantity  of  black  flux, 


FUSION   WITH    METALLIC    IRON.  453 

or  indeed  of  argol,  or  in  mixing  a  few  per  cent,  of  pow- 
dered charcoal  or  flour  with  the  potassium  carbonate,  or 
in  replacing  it  in  part  by  argol.  Too  great  an  addition  of 
carbon  diminishes  the  fusibility  of  the  mass,  and  hinders 
the  flowing  together  of  the  separated  particles  of  lead.  By 
using  argol  the  operation  lasts  longer,  because  the  mass 
remains  pasty  until  most  of  the  tartaric  acid  has  been 
decomposed  ;  but  a  greater  product  of  lead  is  obtained. 
The  chemical  reaction  during  the  operation  is  thereby 
modified  so  that  the  carbon  of  the  black  flux  exerts  an 
influence  upon  the  potash,  and  partiaUy  reduces  it  to 
potassium  ;  the  potassium,  thus  set  free,  works  now,  as 
before,  upon  the  galena.  The  latter  is  thus,  without  the 
influence  of  the  air,  more  completely  decomposed  than  by 
potassium  carbonate  alone,  and  the  smelting  is,  therefore, 
conducted  in  covered  crucibles  (fig.  61)  in  the  wind  fur- 
nace. But  since  there  is  also  potassium  sulphide  formed, 
and  this  dissolves  lead  sulphide,  it  is  more  advisable,  for 
the  completest  possible  separation  of  the  lead,  to  perform 
the  smelting  in  open  crucibles  in  the  muffle,  in  order  to 
allow  the  atmospheric  oxygen  to  work  at  the  same  time 
on  the  assay.  The  product  of  lead  from  pure  galena  does 
not  generally  exceed  76  to  79  per  cent. 

At  the  Victor-Frederick  smelting  works  in  the  Hartz, 
one  centner  (=  one  hundred  and  fourteen  pounds)  of 
galena  is  mixed  with  three  or  four  times  as  much  black 
flux,  and  with  pyritic  ores  ten  pounds  of  borax-glass  are 
added.  The  mixture  is  covered  with  sodium  chloride, 
heated  for  about  twenty-five  minutes  in  the  muffle  furnace 
with  a  charcoal  fire,  and  then,  after  the  mouth  of  the 
muffle  has  been  opened  for  about  five  minutes,  taken  out 
of  the  furnace. 


3.    FUSION   WITH   METALLIC   IRON. 

Schlutter  and  many  of  the  older  assayers  were  aware 
that  iron  would  desulphurise  galena,  and  ever  after  advised 
the  addition  of  a  certain  quantity  of  that  metal  to  the 
different  fluxes  which  they  used  in  lead  assays ;  but  it  was 


454  THE    ASSAY    OF    LEAD. 

at  the  practical  School  of  Mines,  at  Montiers,  that  iron 
was  first  employed  alone. 

The  process  is  extremely  convenient  and  easy  of  exe- 
cution ;  it  always  succeeds,  and  requires  no  troublesome 
attention.  The  fusion  takes  place  quietly,  without  frothing 
or  bubbling  ;  and  as  the  whole  substance  employed  requires 
but  little  space,  very  small  pots  may  be  employed,  or  a 
very  large  quantity  assayed.  But  this  process  can  only 
be  employed  for  pure  galenas,  or  those  which  contain  at 
most  a  few  per  cent,  of  gangue. 

When  galena  is  heated  with  iron,  the  metal  is  trans- 
formed into  protosulphide,  whence  it  follows,  that  to  de- 
sulphurise galena  22- 6  per  cent,  is  required ;  but  expe- 
rience has  shown  that  it  is  better  to  employ  a  little  more, 
and  30  per  cent,  can  be  used  without  inconvenience.  The 
iron  employed  ought  to  be  in  the  state  of  filings,  or  wire 
cut  very  small.  The  mixture  is  placed  in  a  crucible, 
which  is  three-fourths  filled ;  the  whole  is  covered  with  a 
layer  of  salt,  sodium  carbonate,  or  black  flux,  and  exposed 
to  a  full  red  heat.  After  the  flux  is  perfectly  fused,  the 
pot  may  be  cooled  and  broken,  and  a  button  is  obtained, 
which  at  first  sight  has  a  homogeneous  aspect,  but  on 
being  struck  with  the  hammer  separates  into  two  distinct 
parts.  The  lower  part  is  ductile  lead  :  the  upper  a  very 
brittle  matt,  of  a  deep  bronze  colour,  and  slightly  mag- 
netic. Pure  galena  yields,  by  this  process,  72  to  79  per 
cent,  of  lead,  so  that  there  is  a  considerable  loss,  which 
loss  is  entirely  due  to  volatilisation.  Berthier  says  that 
it  does  not  appear  possible  to  avoid  this  loss,  which 
amounts  from  6  to  13  per  cent.,  giving  as  a  reason  that  it 
is  probable  galena  begins  to  sublime  before  it  arrives  at 
the  proper  heat  for  decomposition. 

Antimonial  galenas,  or  galenas  mixed  with  iron  pyrites, 
may  be  assayed  in  the  same  manner  ;  but  then  a  sufficiency 
of  iron  must  be  added  to  reduce  the  antimony  to  the 
metallic  state,  as  well  as  to  reduce  the  iron  pyrites  to  the 
minimum  of  sulphurisation.  If  the  galena  be  mixed  with 
blende,  the  greater  portion  remains  in  the  slag,  because  it 
is  only  decomposed  by  iron  at  a  very  high  temperature. 


FUSION   WITH   METALLIC   IRON.  455 

Blende  being  infusible  by  itself,  much  diminishes  the 
fusibility  of  the  matts  produced  ;  and  if  it  exists  in  very 
large  quantity,  it  can  even  hinder  their  complete  fusion  ;  in 
which  case,  some  iron  protosulphide  and  metalhc  iron  must 
be  added  to  the  assay,  to  make  the  slag  more  fusible. 

All  minerals  are  at  a  minimum  of  sulphurisation  when 
existing  in  matts  from  metallurgical  works  ;  therefore, 
much  less  iron  may  be  used  in  their  assay  than  if  they 
were  pure  ores.  In  very  rich  lead  matts,  in  which  the 
lead  exists  as  subsulphide,  from  10  to  12  per  cent,  is 
sufficient.  A  small  excess  of  iron  may  be  employed  with- 
out inconvenience ;  but  if  a  larger  proportion  be  added 
than  is  necessary  to  execute  the  desulphurisation,  the  matt 
contains  some  iron  in  the  metallic  state,  and  loses  its 
liquidity,  and  in  consequence  retains  some  globules  of 
lead. 

The  usual  mode  of  assaying  lead  ores  (galena)  in  the 
lead  mills  is  by  a  modification  of  this  process :  in  lieu  of 
placing  the  ore  in  an  earthen  crucible,  and  adding  nails  or 
filings,  a  given  weight  of  the  ore  is  projected  into  a  red- 
hot  wrought-iron  crucible,  which  is  kept  in  the  fire  for 
about  a  quarter  of  an  hour,  or  until  all  the  galena  seems 
decomposed.  The  lead  thus  reduced  is  poured  into  a 
mould  ;  and  if  the  scoriaceous  matter  be  not  well  fused, 
the  iron  crucible  is  returned  to  the  fire  and  heated  still 
more  strongly,  and  any  lead  that  may  be  separated  is 
poured  into  the  mould  and  weighed  with  the  rest.  This 
is  a  very  rude  and  imperfect  process,  and  gives  only 
tolerable  results  with  pure  galenas,  but  is  quite  unsatisfac- 
tory with  those  containing  much  earthy  matter,  as  not 
above  half  the  lead  is  obtained,  owing  to  volatilisation  and 
exposure  to  the  air,  and  the  loss  of  globules  in  the  slag. 
This  process  succeeds  much  better  when  a  flux  is  added ; 
this  may  be  argol,  or  sodium  carbonate,  or  a  mixture  of 
both  (see  next  process). 


456  THE   ASSAY   OF    LEAD. 


4.    FUSION   WITH   SODIUM   CARBONATE    OR   BLACK   FLUX,    AND 
METALLIC   IRON. 

When  galena  is  heated  with  an  alkaline  Hux,  out 
of  contact  of  air,  the  slag  contains  a  double  sulphide  of 
lead  and  the  alkaline  metal  employed :  if  iron  be  thrown 
into  this  fused  mixture,  metallic  lead  separates,  and  the 
iron  combines  with  the  sulphur  formerly  combined  with  the 
lead,  and  the  slag  will  contain  a  double  alkaline  sulphide, 
containing  iron  sulphide  instead  of  lead  sulphide,  thus  : 

PbS + K2S  -H  Fe = Pb2  +  FeSK2S. 

Any  earthy  substances  the  ore  may  contain  will  be 
dissolved  by  the  alkaline  flux,  without  very  much  impair- 
ing its  fluidity.  All  these  facts  being  considered,  it  may 
be  readily  seen  that  the  assay  of  all  earthy  bodies  contain- 
ing lead  sulphide  may  be  made  in  this  manner,  with  as 
much  accuracy  as  this  method  of  assay  can  be  capable  of. 
Either  sodium  carbonate  or  black  flux  may  be  employed 
as  the  alkaline  reagent,  and  more  of  either  of  those 
substances  must  be  employed,  in  proportion  to  the  in- 
creased quantity  of  earthy  matters  the  ore  contains.  Two 
parts  are  nearly  always  more  than  sufficient  for  poor 
ores,  and  are  best  for  all  cases,  because  an  excess  of  flux 
does  not  diminish  the  yield  of  lead ;  nevertheless,  it  is 
sometimes  convenient  to  employ,  for  the  latter  class,  but 
half  a  part.  As  to  the  iron,  it  is  employed  only  to 
separate  that  part  of  the  lead  which  has  been  dissolved  in 
the  state  of  sulphide  by  the  alkali,  but  not  decomposed  ; 
so  that  much  less  may  be  employed  than  is  necessary  for 
the  decomposition  of  the  whole  amount. 

Experiment  has  shown  that  the  maximum  amount  of 
lead  from  pure  galena  may  be  obtained  by  the  use  of  the 
following  mixtures : — 

2  parts  of  black  flux,  or  sodium  carbonate,  and  10  to 
12  per  cent,  of  iron. 

1  part  of  black  flux,  or  sodium  carbonate,  and  20  per 
cent,  of  iron. 


ROASTING   AND   REDUCING   ASSAY.  457 

^  a  part  of  black  flux,  or  sodium  carbonate,  and  from 
25  to  30  per  cent,  of  iron. 

When  black  flux  is  employed,  and  the  iron  is  in  the 
state  of  filings,  it  would  be  inconvenient  to  employ  too 
much  of  the  latter,  especially  if  the  assay  were  heated 
very  strongly,  because  the  button  of  lead  might  be  con- 
taminated with  iron ;  but  when  sodium  carbonate  is  used 
with  small  iron  nails  instead  of  filings,  the  excess  of  iron 
is- not  inconvenient,  but  rather  useful,  because  the  desul- 
phurisation  is  certain  to  be  complete.* 

The  following  changes  take  place  in  both  cases.  That 
portion  of  iron  filings  mixed  with  the  sodium  carbonate 
which  has  not  been  sulphurised,  is  reduced  to  the  state  of 
oxide  by  the  carbonic  acid  of  the  alkaline  carbonate,  and 
remains  combined  or  neglected  in  the  slag  ;  so  that  the 
proportion  of  iron  is  never  too  great,  and  never  becomes 
mixed  with  the  lead.  When  black  flux  is  employed,  the 
same  oxidation  does  not  take  place,  on  account  of  the 
presence  of  carbonaceous  matter,  so  that  the  portion  of 
filings  not  combined  with  sulphur,  and  which  is  merely 
held  in  suspension  in  the  flux,  passes  through  it  with  the 
globules  of  lead  to  the  bottom  of  the  crucible  :  but  if, 
instead  of  filings,  small  nails  are  employed,  they  only  suffer 
corrosion  at  their  surface,  without  change  of  form  or  soften- 
ing, and  after  the  assay  are  found  fixed  in  the  surface  of 
the  button  of  lead,  so  that  they  can  be  detached  very 
readily,  and,  according  to  Berthier,  without  loss  of  lead. 
This,  however,  we  have  found  no  easy  task,  and  have 
always  sustained  a  notable  loss. 


5.    ROASTING   AND   REDUCING   ASSAY. 

This  mode  is  preferable  for  ores  and  substances  which 
contain  a  considerable  quantity  of  foreign  sulphides,  or 
arsenides  and  antimonides,  and  a  greater  or  less  amount  of 

*  The  French  assayers  use  a  piece  of  plate  iron  in  the  shape  of  a  horse-shoe, 
which  is  moved  about  in  the  melted  mass  until  no  more  globules  of  lead  attach 
themselves  to  it. 

In  Germany  a  piece  of  iron-wire  is  used.  What  iron  is  not  consumed  by 
the  assay  is  found  still  hanging  together  in  a  single  mass. 


458  THE   ASSAY    OF    LEAD. 

earthy  matter.  It  is  used  in  many  parts  of  Germany  (at 
the  Unterhartz),  and  is  described  by  Kerl  thus  : — 

Two  assay  centners  of  ore,  matt,  &c.,  are  heated  at  first 
at  a  low  red  heat  in  the  muffle,  on  a  roasting  dish  that  has 
been  previously  rubbed  with  chalk.  After  ten  or  fifteen 
minutes,  they  are  taken  out  of  the  furnace,  then  again 
roasted  at  a  moderate  temperature  for  ten  or  fifteen  minutes 
with  frequent  turning  of  the  dish.  The  assay  is  then  once 
more  taken  from  the  furnace,  allowed  to  cool,  rubbed  up 
in  an  agate  mortar,  and  again  roasted  for  half  an  hour, 
whereupon  it  is  taken  out  of  the  furnace  ;  tallow  is  added 
while  it  yet  glows,  and  it  is  again  brought  to  a  strong  red 
heat.  The  rubbing  up  and  calcining  with  tallow  are 
repeated  several  times  more,  and  when  afterwards  the 
assays  have  been  exposed  for  two  hours  continuously  to  a 
strong  red  heat,  with  the  mouth  of  the  muffle  almost  en- 
tirely closed,  if  no  more  sulphurous  acid  vapours  escape, 
the  roasting  is  considered  as  finished.  This  lasts  from  six 
to  twelve  hours.  The  roasted  sample  is  then  portioned 
out  with  the  balance,  each  portion  mixed  with  three  or 
four  parts  of  black  flux  and  an  equal  quantity  of  borax 
and  glass,  placed  in  a  small  crucible  covered  with  sodium 
chloride,  furnished  with  a  little  piece  of  coal  as  a  cover, 
and  smelted  in  the  wind  furnace  for  about  a  quarter  of  an 
hour  after  the  fire  is  well  ignited.  Assays  that  have 
worked  well,  give  nearly  equal  malleable  buttons  that  do 
not  contain  matt,  and  a  black  uniformly  fused  slag. 

The  purpose  of  the  roasting  is  to  convert  the  metallic 
sulphides,  arsenides,  and  antimonides  into  oxides.  But 
since  in  the  process,  sulphates,  antimoniates,  and  arseniates 
are  produced,  we  seek  to  destroy  these  by  repeated  cal- 
cining with  tallow  (see  above),  instead  of  an  intermixture 
of  coal-dust  or  flour.  By  melting  the  roasted  assay  with 
its  charge  at  not  too  high  a  temperature,  the  lead  oxide  is 
reduced,  and  the  foreign  oxides  and  earths  contained  in 
the  sample  are,  by  the  aid  of  the  potash  in  the  black  flux, 
as  well  as  of  the  borax  and  glass,  slagged  off.  If  sulphates 
or  sulphides  have  remained  behind  in  the  roasted  ore, 
they  will  in  the  smelting  be  partially  desulphurised  by  the 


ASSAY   WITH    SULPHURIC   ACID.  459 

action  of  the  oxides,  especially  of  the  iron  oxide.  An 
addition  of  metallic  iron  would  in  this  respect  be  advan- 
tageous. 

The  roasting  is  a  lengthy  process,  and  one  which  causes 
a  not  unimportant  loss  of  lead.  If  it  is  not  done  tho- 
roughly, then  in  the  reduction  smelting,  sulphur  salts 
are  formed,  which  always  retain  lead,  as  also  a  plumbi- 
ferous  matt,  which  surrounds  the  lead  button.  By  the 
use  of  too  high  a  temperature  in  the  smelting,  a  great  part 
of  the  foreign  oxides  is  reduced,  and  the  lead  becomes 
contaminated.  The  reduction,  however,  cannot  be  entirely 
avoided,  even  with  a  rightly  conducted  temperature. 

Galena  melts  less  easily  than  metallic  lead  if  the  air 
is  excluded  ;  but  is  much  more  volatile  than  the  latter, 
and  is  decomposed  by  fusion  into  a  higher  sulphide  which 
is  volatile,  and  a  lower  one  (Pb2S)  which  remains  as 
a  residue.  Galena  by  roasting  gives  a  mixture  of  lead 
oxide  and  sulphate,  from  which  last  the  sulphuric  acid 
cannot  be  separated,  even  at  a  fusing  temperature.  Lead 
sulphate  becomes  soft  by  heat,  fuses  at  a  bright  white 
heat,  and  is  converted  by  carbon,  with  a  considerable  loss 
of  lead  through  volatilisation,  into  lead  oxide,  metallic  lead, 
or  lead  subsulphide,  according  to  the  quantity  of  carbon 
used,  and  the  temperature  employed.  With  lead  oxide, 
the  sulphate  easily  fuses  together. 

6.    ASSAY  WITH  SULPHURIC  ACID. 

The  assay  sample  is  rubbed  as  fine  as  possible.  A 
suitable  quantity  of  it  is  then  weighed  out  for  an  assay, 
and  boiled  with  four  to  eight  times  its  weight  of  oil  of  vitriol 
until  all  is  decomposed.  All  excess  of  sulphuric  acid  is 
then  evaporated  in  a  porcelain  capsule,  under  a  flue  with  a 
good  draught,  and  the  mass  carried  to  dryness.  Boiling 
sulphuric  acid  decomposes  the  sulphides,  changing  iron, 
copper,  nickel,  zinc,  &c.,  into  salts  which  dissolve  readily 
in  water,  and  also  at  the  same  time  changing  the  lead 
sulphide  into  sulphate,  which  in  water,  especially  when 
cold,  and  containing  free  sulphuric  acid,  is  practically  in- 


460  THE    ASSAY    OF    LEAD. 

soluble.  The  composition  of  the  ore  is  in  general  ascer- 
tained by  first  heating  it  with  nitric  acid  or  aqua  regia, 
and  then  with  the  addition  of  sulphuric  acid,  evaporating 
to  dryness.  The  dry  mass,  when  cold,  is  moistened  with  a 
small  quantity  of  sulphuric  acid,  then  cold  water  ;  it  is 
afterwards,  by  the  aid  of  a  small  brush,  brought  without 
loss  upon  a  small  filter,  and  washed  with  cold  water  until 
the  filtrate  is  colourless.  Unnecessary  prolonging  of  the 
washing  is  to  be  avoided,  for  lead  sulphate  is  not  absolutely 
insoluble.  The  filter,  with  its  contents,  is  dried  in  the 
funnel,  until  it  can  be  easily  taken  out  of  it  without  tear- 
ing. It  is  now  put  immediately  into  the  clay  crucible,  in 
which  the  lead  sulphate  is  afterwards  to  be  reduced,  and 
this  is  placed  in  a  very  gentle  stove  warmth.  (Some 
potassium  carbonate  may  be  first  poured  into  the  bottom 
of  the  crucible.)  When  completely  dry,  the  crucible  with 
the  cover  laid  over  it  is  very  gently  heated,  so  that  the 
filter  carbonises,  which  very  soon  happens,  as  the  free 
sulphuric  acid  is  not  completely  soaked  out.  The  filter  is 
now  stirred  up  with  a  little  rod,  black  flux  or  potassium 
carbonate  with  coal-dust  and  iron  are  introduced  into  the 
crucible,  and  intimately  mixed  with  the  lead  sulphate  and 
the  rest  of  the  insoluble  residue.  About  four  or  five  times 
the  volume  of  the  whole  residue  is  taken  of  black  flux, 
and  the  assay  is  further  treated  as  prescribed  in  the  portion 
which  follows  upon  the  assaying  of  lead  sulphate. 

In  this  way  the  lead  is  concentrated,  and  the  foreign 
sulphides,  which  were  specified  above  as  the  cause  of  the 
failure  of  the  assay  in  such  cases,  completely  removed. 
The  result  obtained  in  this  way  is  satisfactory,  and  de- 
serves the  same  confidence  as  one  obtained  in  favourable 
circumstances  by  the  ordinary  lead  assay  from  an  ore  with 
a  medium  or  high  percentage  of  lead. 

7.    ASSAY    OF   GALENA   IN   THE   WET   WAY. 

When  in  contact  with  metallic  zinc,  galena  is  readily 
decomposed  by  acids.  Even  oxalic,  acetic,  and  dilute 
sulphuric  acids  are  capable,  when  hot,  of  decomposing 


ASSAY    OF    GALENA.  461 

galena, — metallic  lead  being  deposited  and  sulphuretted 
hydrogen  gas  set  free, — while  with  hydrochloric  acid  the 
decomposition  is  peculiarly  rapid  and  complete. 

Galena  is  easily  decomposed,  also,  even  in  the  cold  by 
dilute  nitric  acid  in  presence  of  zinc ;  but  the  reaction 
differs  in  this  case  from  that  just  described — not  metallic 
lead  but  free  sulphur  is  deposited,  while  lead  nitrate  goes 
into  solution. 

The  reaction  with  zinc  and  hydrochloric  acid  has  been 
employed  with  advantage  by  Mr.  F.  H.  Storer,  Professor  of 
Chemistry  in  the  Massachusetts  Institute  of  Technology, 
for  assaying  galena,  particularly  the  common  American 
variety,  which  contains  no  other  heavy  metal  besides  lead. 
The  details  of  the  process  are  as  follows  : — Weigh  out  2  or 

3  grms.  or  more  of  the  finely  powdered  galena.    Place  the 
powder  in  a  tall  beaker,  together  with  a  smooth  lump  of 
pure  metallic  zinc.  Pour  upon  the  mixed  mineral  and  metal 
100  or  150  c.c.  of  dilute  hydrochloric  acid  which  has  been 
previously  warmed  to  40°  or  50°  C.  ;  cover  the  beaker  with 
a  watch-glass  or  broad  funnel,  and  put  it  in  a  moderately 
warm  place. 

Hydrochloric  acid  fit  for  the  purpose  may  be  prepared 
by  diluting  1  volume  of  the  ordinary  commercial  acid  with 

4  volumes  of  water.     For  the   quantity  of  galena  above 
indicated,  the  lumps  of  zinc  should  be  about  an  inch  in 
diameter  by  a  quarter   of  an  inch   thick ;  they   may  be 
readily  obtained  by  dropping  melted  zinc  upon  a  smooth 
surface  of  wood  or  metal. 

The  zinc  and  acid  should  be  allowed  to  act  upon  the 
mineral  during  fifteen  or  twenty  minutes  in  order  to  ensure 
complete  decomposition.  Any  particles  of  galena  which 
may  be  thrown  up  against  the  cover  or  sides  of  the  beaker 
should  of  course  be  washed  back  into  the  liquid.  It  is 
well,  moreover,  to  stir  the  mixture  from  time  to  time  with 
a  glass  rod. 

When  all  the  galena  has  been  decomposed,  as  may  be 
determined  by  the  facts  that  the  liquid  has  become  clear, 
and  that  no  more  sulphuretted  hydrogen  is  evolved,  decant 
the  liquid  from  the  beaker  into  a  tolerably  large  filter  of 


462  THE   ASSAY    OF    LEAD. 

smooth  paper,  in  which  a  small  piece  of  metallic  zinc  has 
been  placed.  Wash  the  lead  and  zinc  in  the  beaker  as 
quickly  as  possible  with  hot  water,  by  decantation,  until 
the  liquid  from  the  filter  ceases  to  give  an  acid  reaction 
with  litmus  paper  ;  then  transfer  the  lead  from  the  beaker 
to  a  weighed  porcelain  crucible.  In  order  to  remove  any 
portions  of  lead  which  adhere  to  the  lump  of  zinc,  the 
latter  may  be  rubbed  gently  with  a  glass  rod,  and  after- 
wards with  the  finger  or  a  piece  of  caoutchouc,  if  need  be. 
Wash  out  the  filter  into  an  evaporating  dish,  remove  the 
fragment  of  zinc,  and  add  the  particles  of  lead  thus  collected 
to  the  contents  of  the  crucible.  Finally,  dry  the  lead  at  a 
moderate  heat  in  a  current  of  ordinary  illuminating  gas, 
and  weigh. 

The  lead  may  be  conveniently  dried  by  placing  the 
crucible  which  contains  it  in  a  small  cylindrical  air-bath 
of  Eammelsberg's  pattern,  provided  with  inlet  and  outlet 
tubes  of  glass,  reaching  almost  to  the  bottom  of  the  bath. 

When  the  process  is  conducted  as  above  described, 
the  lead  undergoes  no  oxidation ;  hence  there  is  no  occa- 
sion for  igniting  the  precipitate  in  a  reducing  gas.  The 
precipitate  needs  only  to  be  dried  out  of  contact  with 
the  air. 

If  desirable,  the  sulphur  in  the  galena  could  be  deter- 
mined at  the  same  time  as  the  lead,  by  arresting  the 
sulphuretted  hydrogen  in  the  ordinary  way. 

If  the  mineral  to  be  analysed  is  contaminated  with  a 
siliceous  or  other  insoluble  gangue,  the  metallic  lead  may 
be  dissolved  in  dilute  nitric  acid  after  weighing,  and  the 
insoluble  impurity  collected  and  weighed  by  itself.  In  the 
case  of  galenas  which  contain  silver,  antimony,  copper,  or 
other  metals,  precipitable  by  zinc,  the  proportion  of  each 
metal  must  be  determined  by  assay  or  analysis  in  the  usual 
way,  after  the  total  weight  of  the  precipitated  metals  has 
been  taken. 

Besides  galena,  almost  any  of  the  ordinary  lead  com- 
pounds may  evidently  be  assayed  by  the  method  above 
described.  For  example,  metallic  lead  may  be  precipitated 
quickly  and  completely  from  the  sulphate,  chromate, 


ASSAY    OF    SUUSTA.VCKS    OF    THK    SKCOM)    CLASS.  IM 

nitrate,  oxide,  and  carbonate — and  with  peculiar  ease  from 
t  IM-  chloride — by  mean^  of  zinc  arid  hydrochloric  acid.  The 
method  would  also  furnish  an  easy  qualitative  test  for  the 
detection  of  baryta  in  white-lead.  When  applied  to  the 
analysis  of  lead  nitrate,  it  would  probably  be  best  to 
decompose  the  nitrate  by  means  of  a  solution  of  sodium 
chloride  before  adding  the  zinc  and  hydrochloric  acid. 

In  all  these  cases  the  decomposition  of  the  lead  salt 
by  the  zinc  is  .so  Complete  that  no  trace  of  coloration  is 
produced  when  sulphuretted  hydrogen-  is  added  to  the 
liquid  decanted  from  the  metallic  lead. 

Attempts  to  determine  sulphur  and  lead  in  the  same 
portion  of  galena,  by  means  of  the  reaction  of  zinc  and 
dilute  nitric  acid  above  described,  have  not  given  satisfac- 
tory results.  The  free  sulphur  obtained  by  treating  galena 
with  zinc  and  ordinary  nitric  acid,  diluted  with  three, 
four,  and  five  volumes  of  water,  always  retains  a  small 
quantity  of  lead,  while  a  certain  amount  of  sulphuric  acid 
is  found  in  the  clear  liquid.  It  is,  in  short,  well-nigh,  or 
quite  impossible  to  avoid  the  secondary  reactions  between 
zinc  and  lead  nitrate,  and  between  sulphuric  and  nitric 
acid,  which  set  in  as  soon  as,  or  just  before,  the  last  traces 
of  the  galena  have  been  decomposed. 


CLASS  II. 

Assay  of  Substance*  of  the  Second  Class. — The  assay  of 
these  substances  is  very  simple  indeed.  Litharge,  minium, 
lead  carbonate,  &c.,  may  be  assayed  by  simple  fusion  with 
carbonaceous  matter ;  but  when  the  operation  is  thus 
conducted,  loss  of  lead  is  sustained  :  it  is  therefore  better 
to  add  some  flux  which  will  readily  fuse,  and  allow  the 
globules  of  reduced  lead  to  collect  into  one  button.  No 
flux  fulfils  this  condition  better  than  a  mixture  of  sodium 
carbonate  arid  argol,  which  is  to  be  intimately  mixed  with 
the  assay.  The  following  is  the  best  mode  of  procedure : — 
To  ^00  grains  of  the  finely-pulverised  substance  add  100 
grains  of  argol,  and  300  of  sodium  carbonate,  arid  inti- 


464  THE    ASSAY    OF    LEAD. 

mately  mix  ;  place  the  mixture  in  a  crucible  which  it 
about  half  fills,  and  cover  with  a  layer  of  common  salt 
about  £  inch  thick  ;  submit  the  crucible  to  a  very  gradu- 
ally increasing  temperature,  keeping  the  heat  at  low 
redness  for  about  a  quarter  of  an  hour ;  then  urging  it  to 
bright  red  until  the  contents  of  the  crucible  flow  freely  ; 
take  it  from  the  fire  and  shake,  tap  it  as  directed  in  the 
copper  assay,  and  either  pour  the  contents  into  the  mould 
or  allow  to  cool  in  the  crucible.  If  the  operator  be 
pressed  for  time,  the  mould  may  be  used,  but  it  is  recom- 
mended to  allow  the  assay  to  cool  in  the  crucible,  for 
unless  the  operator  be  very  careful,  and  have  had  some 
considerable  practice,  he  is  very  liable  to  lose  a  small 
quantity  of  metal  in  the  pouring.  After  the  contents  of 
the  mould  or  crucible,  as  the  case  may  be,  are  cold,  the 
lead  may  be  separated  from  the  slag  by  repeated  gentle 
blows  from  the  hammer  :  if  any  of  the  slag  or  crucible 
adhere  to  the  button,  the  latter  may  be  readily  freed  from 
it  by  placing  the  button  between  the  finger  and  thumb 
with  its  edge  on  the  anvil,  and  then  gently  hammering  it. 
The  lead  will  be  so  altered  in  shape  under  the  hammer 
that  the  slag  or  crucible  readily  falls  off;  and  by  continu- 
ing the  process,  the  whole  may  be  removed.  The  cleaned 
button  may  then  be  hammered  into  a  cubical  form,  and 
is  ready  for  weighing. 

In  the  assay  of  lead  great  care  must  be  taken  in  the 
management  of  the  temperature,  as  lead  is  sensibly  volatile 
above  a  bright  red  heat,  even  when  covered  with  flux, 
and  still  more  so  if  any  portion  be  uncovered  from  want 
of  sufficient  quantity  of  flux ;  neither  must  the  assay 
remain  in  after  the  flux  flows  freely,  for  a  loss  may  thereby 
occur  from  oxidation,  by  decomposition  of  sodium  carbo- 
nate, as  explained  in  the  reduction  of  copper  ores  and  the 
copper-refining  process. 

For  the  rationale  of  this  mode  of  assay,  refer  to  page 
199,  which  explains  the  decomposition  of  lead  oxide,  with 
the  production  of  metallic  lead,  carbonic  acid,  and  water, 
by  the  agency  of  a  substance,  like  argol,  containing  both 
carbon  and  hydrogen. 


ASSAY   OF   SUBSTANCES   OF   THE   SECOND    CLASS.  465 

Cupel  bottoms,  some  lead  fumes,  and  siliceous  slags, 
require  a  modified  treatment  in  the  assay,  as  the  sub- 
stances mixed  with  the  oxide  of  lead  (more  particularly 
bone-ash  in  the  cupel  bottoms)  are  very  infusible ;  and  if 
the  flux  already  mentioned  as  applicable  to  the  other 
matters  belonging  to  this  class  were  employed,  a  very  high 
temperature  would  be  necessary ;  and  as  lead,  as  already 
stated,  is  sensibly  volatile  above  a  bright  red  heat,  an 
evident  loss  of  that  metal  would  be  the  result. 

Cupel  bottoms  may  be  thus  assayed  :  400  grains  of  the 
finely-pulverised  bottoms  to  be  mixed  with  200  grains  of 
argol,  400  grains  of  sodium  carbonate,  and  400  grains  of 
pulverised  fused  borax  ;  the  mixture  is  placed  in  a  crucible 
as  already  directed,  covered  with  salt,  and  the  fusion  con- 
ducted as  just  described. 

Lead  fumes  and  siliceous  slags  require  only  half  their 
weight  of  fused  borax,  with  200  argol,  400  sodium  car- 
bonate, and  400  substance  (fume  or  slag),  covered  with 
salt. 

The  addition  of  the  borax,  which  is  a  most  powerful 
flux,  causes  the  fusion  of  the  assay  to  take  place  almost  as 
readily  with  the  last-named  refractory  substances  as  with 
the  former  easily  fusible  and  reducible  matters.  The 
assay,  however,  is  rather  more  subject  to  ebullition  or 
boiling  over  the  sides  of  the  crucible ;  hence  it  must  be 
carefully  watched,  and  the  instant  it  appears  likely  to  do 
so  the  crucible  must  be  removed  from  the  fire,  gently 
tapped  on  the  furnace-top,  and  when  the  effervescence 
has  subsided  returned  to  the  furnace,  and  this  operation 
repeated  until  the  fusion  proceeds  tranquilly. 

The  lead  obtained  in  these  assays,  if  the  ore  or  sub- 
stance contained  any  foreign  metal,  is  never  pure :  if  silver, 
copper,  tin,  or  antimony  be  present,  the  whole  of  either 
of  these  metals  will  be  found  alloyed  with  the  lead  pro- 
duced ;  but  if  the  ore  contains  zinc,  and  it  be  heated 
sufficiently,  only  a  trace  remains ;  nevertheless  the  zinc 
carries  off  with  it  a  considerable  quantity  of  lead. 

The  following  experiments  will  show  what  an  influence 
the  presence  of  zinc  has  upon  the  return  of  lead  : — ' 

H  H 


436  THE    ASSAY    OF    LEAD. 

100  parts  of  litharge, 
100  parts  of  zinc  oxide. 
300  parts  of  black  flux, 

were  fused  together,  and  84  parts  of  lead  were  the  result. 
100  parts  of  litharge, 
100  parts  of  zinc  oxide, 
600  parts  of  black  flux, 

were  fused  together,  and  but  70  parts  of  lead  were  pro- 
duced instead  of  90,  which  the  pure  litharge  ought  to 
have  given.  Hence  it  will  be  seen  that,  the  more  zinc  is 
reduced,  the  more  lead  is  volatilised. 

If  iron  oxide  be  present  in  the  assay,  it  is  reduced,  but 
it  remains  in  suspension  in  the  slag,  and  the  lead  does  not 
contain  a  trace  when  it  has  not  been  too  strongly  heated. 
If  the  assay  be  made  at  a  very  high  temperature,  the  iron 
may  be  fused,  and  then  the  lead  will  be  ferruginous  ;  this 
may  be  ascertained  by  means  of  the  magnet.  A  similar 
result  was  obtained  by  many  assayers,  who  thought  for  a 
long  time  that  lead  and  iron  could  thus  combine  together ; 
but  by  careful  examination  it  is  easily  ascertained  that  the 
ferruginous  buttons  are  but  mechanical  mixtures  of  lead 
and  iron  in  grains.  Indeed,  by  careful  hammering,  nearly 
all  the  iron  may  be  removed  from  the  lead,  so  that  it  loses 
its  magnetic  properties. 

The  manganese  oxides,  when  mixed  with  the  ore,  are 
changed  into  protoxide,  which  remains  in  the  flux,  and  is 
not  reduced. 

Wet  Assay  of  Ores  of  the  Second  Class — Pulverise  the 
substance  very  finely,  and  to  100  grains  placed  in  a  flask 
add  one  ounce  of  nitric  acid  diluted  with  two  ounces 
of  water  (if  minium  be  the  substance  to  be  analysed,  it 
must  be  first  heated  to  redness,  so  as  to  reduce  the  whole 
of  the  lead  it  contains  to  the  state  of  protoxide),  and  gently 
heat,  gradually  raising  the  temperature  to  the  boiling- 
point  :  when  all  action  seems  to  have  ceased,  pour  the 
contents  of  the  flask  into  an  evaporating  basin,  and  evapo- 
rate to  dryness  with  the  precautions  directed  in  the  analysis 
of  iron  ore.  Allow  the  dry  mass  to  cool,  add  a  little  dilute 


ASSAY   OF   SUBSTANCES    OF   THE   THIRD   CLASS.  467 

nitric  acid,  gently  warm  for  an  hour,  then  add  water,  boil 
and  filter.  The  whole  of  the  lead  now  exists  in  the  solu- 
tion as  nitrate  :  thus,  say  lead  carbonate  had  been  the 
substance  under  analysis,  then — 

PbO,C02  +  N05 =PbO,N05  +  C02. 

To  the  filtered  solution  containing  the  nitrate  as  above, 
add  solution  of  sodium  sulphate,  or  dilute  sulphuric  acid, 
until  no  further  precipitation  takes  place ;  insoluble  sul- 
phate  of  lead  will  now  be  thrown  down ;  this  must  be 
allowed  to  completely  subside  by  standing  in  a  warm  place  ; 
and  when  the  supernatant  liquid  is  quite  bright,  the  sul- 
phate may  be  collected  on  a  filter,  washed,  dried  in  the 
water-bath,  and  weighed.  It  contains  68'28  per  cent,  of 
metallic  lead. 

The  decomposition  of  the  lead  nitrate  by  sodium  sul- 
phate may  be  thus  expressed — 

PbO,N05 + j^a20,S03=PbO,S03  +  Na20,N05. 

Determination  of  lead  by  standard  solution  will  be 
described  at  the  end  of  this  chapter. 


CLASS  III. 

Assay  of  Substances  of  the  Third  Class. — In  the  assay 
of  bodies  belonging  to  this  class,  a  reducing  agent  must  be 
employed ;  but  if  that  alone  be  used,  the  sulphates  and 
arseniates  produce  sulphides  and  arsenides,  and  not  pure 
lead.  The  action  of  another  reagent  is  therefore  necessary, 
in  order  to  deprive  the  lead  of  the  sulphur  and  arsenic 
with  which  it  is  combined. 

There  are  two  reagents  employed  for  the  sulphates — 
the  alkaline  carbonates  and  metallic  iron ;  but  for  the 
arseniates  and  arsenites  iron  must  be  employed,  because 
the  alkaline  carbonates  have  no  action  on  the  arsenides. 

In  all  cases  black  flux  is  employed ;  this  furnishes  a 
reducing  agent  for  the  oxides,  and  a  flux  for  the  earthy 
matters.  Iron  is  added  when  the  arsenites  or  arseniates 
are  assayed ;  but  that  metal  may  either  be  employed  or 

H  H  2 


4(38  THE   ASSAY   OF    LEAD. 

not,  when  the  sulphates  are  operated  upon.  It  is,  how- 
ever, always  better  to  use  it. 

When  a  mixture  of  black  flux  and  iron  is  employ edy 
the  assay  is  made  in  exactly  the  same  manner  as  that  of 
the  sulphides  (large  nails  are  preferable  whenever  the  use 
of  iron  is  indicated  in  a  lead  assay).  With  the  sulphate, 
the  iron  sulphide  formed  combines  in  the  slag  with  the 
alkaline  sulphide  ;  but  it  is  not  so  with  the  arseniates  and 
arsenites.  The  arsenide  produced  mixes  neither  with  the 
lead  nor  the  slag,  but  gives  rise  to  the  formation  of  a  brittle 
matter  which  adheres  slightly  to  the  button  of  lead. 

When  only  black  flux  is  employed,  either  of  the  two 
following  processes  may  be  adopted : — First,  the  ore  can 
be  fused  with  four  parts  of  common  black  flux ;  then,  as 
in  the  case  of  sulphides,  the  expess  of  carbon  determines 
the  formation  of  a  large  quantity  of  an  alkaline  sulphide  ; 
and  consequently  produces  a  desulphurisation  of  the  lead. 
Secondly,  it  may  be  fused  with  such  a  proportion  of  black 
flux,  containing  only  the  requisite  proportion  of  carbon  to 
reduce  the  lead  oxide,  or  with  an  equivalent  mixture  of 
sodium  carbonate  and  charcoal.  Pure  lead  sulphate  fused 
with  one  part  of  sodium  carbonate  and  4  per  cent,  of  char- 
coal gives  66  of  lead ;  but  in  order  to  employ  this  method 
the  richness  of  the  ore  must  be  known,  and  the  dry  way 
is  then  useless,  excepting  for  the  estimation  of  the  silver 
these  substances  always  contain. 

Wet  Assay  of  Substances  of  the  Third  Class. — These 
are  treated  in  precisely  the  same  manner  as  those  of  the 
preceding  class. 

In  treating  lead  ores  with  nitric  acid  a  loss  generally 
results  from  the  formation  of  insoluble  lead  sulphate.  The 
solubility  of  these  salts  in  sodium  hyposulphite  renders  it 
possible  to  avoid  this  inconvenience.  After  treatment  with 
nitric  acid,  J.  Groeme  (Bulletin  de  la  Soc.  Chimique  de 
Paris,  November  5,  1873)  proposes  to  exhaust  the  residue 
with  boiling  water,  until  the  soluble  salts  and  the  acid  are 
completely  eliminated.  It  is  then  digested  in  the  cold  with 
a  concentrated  solution  of  sodium  hyposulphite.  After  this 
treatment  has  been  twice  or  thrice  repeated,  the  residue 


ASSAY   OF   SUBSTANCES   OF   THE   THIRD    CLASS.  469 

Is  exhausted  again  with  water  ;  the  lead  is  then  precipitated 
from  the  nitrate  by  sulphuretted  hydrogen  or  ammonium 
•sulphide ;  to  facilitate  the  agglomeration  of  the  precipitate 
.and  its  washing,  it  is  heated  in  the  water-bath.  The  sul- 
phide is  then  converted  into  sulphate,  and  its  weight  added 
to  that  of  the  sulphate  obtained  directly. 

F.  Maxwell  Lyte  thinks  the  following  process  for  the 
management  of  the  assay  of  lead  in  ores  will  be  found 
convenient,  particularly  where,  as  is  often  the  case,  the 
lead  to  be  estimated  is  mixed  as  sulphate  with  the  matrix 
insoluble  in  acid. 

He  dissolves  the  sulphate  or  chloride,  as  the  case  may 
be,  in  ammonium  acetate,  makes  the  solution  as  neutral  as 
possible,  and  estimates  the  lead  by  a  standard  solution  of 
bichromate  (a  half  decinormal  solution  answers  well)  with 
a  silver  nitrate  indicator. 

A.  Mascazzini,  previous  to  reducing  the  galena  or  other 
lead  ore  to  the  metallic  state,  converts  the  lead  present  in 
the  ore  into  sulphate  by  igniting  it  in  a  porcelain  crucible 
with  ammonium  sulphate,  after  which  the  ore  is  treated  in 
the  usual  manner.  The  flux  preferred  by  the  author  is 
that  recommended  by  Plattner,  consisting  of  13  parts  of 
potassium  carbonate,  10  of  dry  sodium  carbonate,  5  of 
previously  fused  borax,  and  5  of  well-dried  starch. 

To  detect  galena  in  mixtures,  M.  E.  Jannesay  throws 
upon  coarsely  powdered  galena  a  fragment  of  potassium 
bisulphate,  which  gives  a  distinct  evolution  of  sulphuretted 
hydrogen.  If  the  two  bodies  are  ground  together  the 
odour  becomes  almost  insupportable.  Potassium  bisul- 
phate kept  in  fusion  for  half  an  hour  produces  the  same 
effect,  perhaps  with  less  intensity.  Sulphuric  acid,  mixed 
or  even  heated  with  galena,  does  not  give  rise  to  a  sen- 
sible disengagement  of  sulphuretted  hydrogen.  Blende 
gives  a  sulphydric  odour,  but  less  intense.  Antimony, 
iron,  mercury,  and  silver  sulphides  give  off  no  sensible 
odour.  Boulangerite,  zinbrenite,  and  in  general  the  sul- 
phides in  which  lead  and  sulphur  do  not  form  an  isolated 
combination,  do  not  yield  their  sulphur  to  the  potassium 
bisulphite. 


470  THE   ASSAY   OP   LEAD. 

CLASS   IV. 

ALLOYS  OF  LEAD. 

ASSAY   WITH    SULPHURIC    ACID. 

No  docimastic  assay  is  known  for  exhibiting  the  lead 
isolated  from  its  alloys.  In  individual  cases  a  serviceable 
result  may  be  attained,  if  the  metal  with  which  the  lead  is 
combined  be  determined,  and  its  quantity  then  deducted. 
This  method  is,  however,  in  general,  the  more  unreliable 
the  smaller  is  the  quantity  of  lead,  or  when  the  lead  is 
alloyed  with  several  metals  ;  so  that  then  the  quantity  of 
lead  can  often  only  be  determined  by  the  partial  or  com- 
plete aid  of  the  wet  way. 

For  many  products  (e.g.,  crude  lead,  hard  lead — con- 
taining antimony  or  arsenic — plumbiferous  copper,  &c.), 
the  assay  with  sulphuric  acid  described  on  page  459  is 
suitable.  One  assay  centner  of  the  substance  is  decom- 
posed by  nitric  acid  or  aqua  regia,  then,  with  the  addition 
of  sulphuric  acid,  evaporated  to  dry  ness,  and  the  dry  mass 
treated  as  above  directed.  If  the  residue  consists  only  of 
lead  sulphate,  it  can  be  brought  upon  a  weighed  filter,  and 
from  the  weight  of  the  residue  after  drying,  the  amount 
of  lead  may  be  calculated.  100  parts  lead  sulphate  contain 
68*33  parts  lead. 

ADDITIONAL    REMARKS    ON    THE    LEAD    ASSAY. 

Comparison  of  the  Different  Methods  for  the  Docimastic  Deter- 
mination of  Lead  in  their  application  to  various  Products. 

Markus  has  made  the  following  comparative  experi- 
ments with  the  methods  of  assaying  lead  ores  most  in  use 
at  the  Austrian  smelting  works  at  Joachimsthal. 

a.  Assay  with  Black  Flux  and  Iron. — One  assay  centner 
(5 -7  grammes)  of  the  finely  rubbed,  sifted  and  dried  assay 
substance  was  mixed  with  two  assay  centners  of  black  flux, 
made  of  sixteen  saltpetre  and  forty  argol,  and  sixty  pounds 
of  borax-glass  in  a  mixing  capsule,  and  put  into  a  clay 


DOCIMASTIC   DETERMINATION   OF   LEAD.  471 

crucible,  on  the  bottom  of  which  a  piece  of  thick:  iron  wire 
one  inch  long  and  forty  centners  in  weight,  had  been  placed 
in  a  vertical  position.  The  crucible  charge,  covered  over 
with  two  centners  of  decrepitated  sodium  chloride,  was 
smelted  in  a  mineral  coal  muffle  furnace,  with  the  mouth 
of  the  muffle  closed,  and  the  draught  half  open,  at  a  mode- 
rate temperature,  the  temperature  then  lowered  for  six  to 
seven  minutes  by  opening  the  mouth  of  the  muffle,  then 
the  muffle  closed  again  for  an  equal  period,  and  the  final 
heat  then  given.  The  cessation  of  the  low  crackling  of 
the  assay  was  now  carefully  attended  to,  and  this,  ceasing 
after  seven  to  eight  minutes,  indicated  the  completion 
of  the  assay.  The  duration  of  the  assay  was  twenty 
minutes. 

b.  Roasting  and  Reduction  Assay  with  Iron. — One  assay 
centner  of  galena  was  roasted,  at  first  at  a  low  tempera- 
ture, for  about  thirty  minutes  on  a  roasting  dish,  and  the 
dish  then  pushed  into  the  back  part  of  the  muffle  for  six 
to  eight  minutes  to  destroy  the  sulphates  formed.     The 
roasted  ore  was  rubbed  fine,  intimately  mixed  with  three 
hundred  centners  of  black  flux,  and  fifty  centners  of  borax- 
glass,  placed  in  a  crucible  with  a  piece  of  iron  weighing 
twenty  centners  at   the  bottom,  covered  with   salt,  and 
smelted  as  above. 

c.  Roasting  and  Fusing  with  Black  Flux. — One  centner 
of  the  roasted  ore  was  smelted  as  before  with  three  hun- 
dred centners  of  black  flux  and  fifty  centners  of  borax, 
but  without  iron. 

The  results  obtained  proved— 

1.  That  wi'th  all  those  products  which  contain  tolerably 
pure  lead  sulphide,  especially  with  high  percentages,  the 
iron  assay,  a,  gives  in  a  remarkably  predominant  degree 
the  most  lead   (as  high  as  96  per  cent,  of  all  the  lead 
present). 

2.  With  impure  lead  ores,  which  contain  more  foreign 
sulphides,   the   assay   a  gives  likewise   the   highest  per- 
centage, though  the  assays  b  and  c  give  only  a  few  per 
cent.  less. 


472  THE   ASSAY   OF    LEAD. 

3.  If  foreign  sulphides  are  present  in  predominant 
quantity,  the  methods  of  b  and  c  give  a  slightly  higher 
percentage  than  that  of  a. 

Level's  Fusion  Assay  with  Potassium  Ferrocyanide  and 
Cyanide. 

According  to  Levol,  the  method  of  assaying  galena  for 
its  lead  by  smelting  it  with  black  flux  and  iron  is  defective 
in  two  respects.  First,  it  is  difficult  to  choose  precisely 
the  quantity  of  iron  required  for  the  reduction  of  the  lead, 
and  a  lack  or  excess  of  it  either  gives  too  little  lead  or  a 
button  containing  iron ;  and  second,  in  order  that  the 
reaction  may  be  complete  and  the  lead  unite  to  a  button, 
we  are  compelled  to  use  a  very  high  temperature,  at  which 
lead  volatilises.  The  first  defect  can  indeed  be  removed 
by  the  use  of  iron  crucibles,  but  these  are  easily  rendered 
unserviceable,  and  require  a  pouring  out  of  the  fused 
mass,  and  then  globules  of  lead  are  apt  to  remain  in  the 
slag. 

By  the  use  of  a  mixture  of  fifty  parts  of  potassium 
cyanide  and  one  hundred  of  anhydrous  potassium  ferro- 
cyanide  to  one  hundred  of  galena,  the  loss  of  lead 
diminishes  to  from  2  to  2^  per  cent.,  probably  in  con- 
sequence of  the  easy  fusibility  of  the  mixture,  and  the 
extremely  fine  division  of  the  iron  in  the  potassium  ferro- 
cyanide.  With  antimonial  galena  this  process  is  not 
applicable,  as  the  antimony  is  reduced  and  goes  into  the 
lead.  Potassium  cyanide  alone,  gives,  by  reason  of  the 
greater  quantity  of  metallic  sulphide  which  it  retains,  a 
smaller  product  of  lead. 

DETERMINATION   OF   LEAD   BY   MEANS   OF   STANDARD   SOLUTIONS. 
1.  FLORES  DUMONTE'S  METHOD. 

Determination  of  Lead  by  means  of  Standard  Solutions. 
This  process  is  due  to  M.  Flores  Dumonte,  and  may  be 
thus  described : — This  mode  of  analysis  is  analogous  to 
that  proposed  by  Pelouze  for  the  determination  of  copper  ; 
advantage  is  taken  of  the  fact  that  oxide  of  lead  is  soluble 


SCHWARTZ'S  METHOD.  473 

in  caustic  potash  in  the  same  manner  that  copper  oxide  is 
soluble  in  ammonia  ;  and  from  either  solution  the  respective 
metal  is  precipitated  by  means  of  a  standard  solution  of 
sodium  sulphide. 

The  solution  of  sodium  sulphide  may  be  conveniently 
made  by  dissolving  one  ounce  of  sodium  sulphide  in  one 
quart  of  water,  and  determining  how  much  of  it  is  necessary 
to  precipitate  twenty  grains  of  lead.  To  this  end  weigh 
off  twenty  grains  of  lead,  dissolve  them  in  nitric  acid,  di- 
lute with  water,  and  add  excess  of  caustic  potash  until  the 
oxide  of  lead  first  thrown  down  is  completely  dissolved. 
The  solution  must  now  be  heated  to  ebullition,  and  the 
sodium  sulphide  gradually  added  from  the  burette  ;  at 
each  addition  a  black  precipitate  of  lead  sulphide  falls. 
The  liquid  is  then  boiled  for  a  short  time,  by  which  means 
it  brightens  ;  more  sodium  sulphide  is  then  added,  and  the 
whole  again  boiled,  and  these  operations  alternately  con- 
tinued until  no  further  coloration  or  blackening  is  pro- 
duced by  the  last  drop  of  sulphide.  The  number  of 
divisions  used  is  then  read  off,  and  the  calculation  made 
as  in  Pelouze's  copper  assay,  substituting  lead  for  copper. 

Having  thus  standardised  the  solution  of  sodium  sul- 
phide, the  assay  of  a  sample  of  ore  may  be  thus  made  : — 
If  the  ore  belong  to  the  first  class,  dissolve  it  in  dilute 
nitric  acid  and  evaporate  to  dryness  ;  to  the  dry  mass  add 
excess  of  caustic  potash  solution,  and  boil ;  after  about 
a  quarter  of  an  hour's  ebullition,  filter  and  throw  down 
the  lead  as  directed,  with  the  standard  solution ;  from  the 
amount  used  calculate  the  quantity  of  lead  present ;  if  the 
ore  be  of  the  second  or  third  class,  treat  with  strong  nitric 
acid  and  sodium  carbonate,  as  already  directed.  The  lead 
carbonate  so  produced  may  be  dissolved  in  either  nitric  or 
acetic  acid,  and  to  the  solution  thus  obtained  add  caustic 
potash,  &c. 

2.  SCHWARTZ'S  METHOD. 

Dissolve  14'730  grammes  of  pure  potassium  bichromate 
in  sufficient  water  to  form  one  litre.  One  cubic  centimetre 
of  this  solution  precipitates  0-0207  gramme  of  lead. 


474  THE   ASSAY   OF    LEAD. 

In  the  estimation  of  pure  lead  a  certain  quantity  of  it 
should  be  dissolved  in  a  minimum  of  nitric  acid,  the  solu- 
tion diluted  with  water,  carefully  neutralised  with   am- 
monia or  sodium  carbonate,  and  excess  of  sodium  acetate 
added,    and  the  solution   precipitated   by  the  potassium 
bichromate  solution.     When  the  precipitation  approaches 
its  end,  or  when  the  precipitate  commences  readily  to 
subside,  some  drops  of  a  neutral  solution  of  silver  nitrate 
are  deposited   on  a  porcelain  plate,  and   the   potassium 
chromate  solution  only  added  by  two  or  three  drops  at  a 
time  to  the  liquid  under  examination  ;  after  each  addition 
the  whole  is  well  stirred,  allowed  to  subside,  and  a  drop  of 
the  clear  supernatant  liquor  added  to  one  of  the  drops  of 
the  silver  solution.     As  soon  as  the  potassium  bichromate 
is  in  excess,  the  two  drops  form  a  red  colour,  while  the 
precipitated  lead  chromate  has  no  effect  on  the  silver  test, 
but   simply   floats   on   the    top    as  a  yellow  precipitate. 
Should  the   solution  assume  a  yellow  colour  before  the 
silver  reaction  has  commenced,  it  would  indicate  that  not 
sufficient  sodium  acetate  had  been  added  in  the  first  in- 
stance, and   it  Avould  be  necessary  to  add  this  now,  and 
also  a  cubic  centimetre  of  a  normal  lead  solution,  contain- 
ing 0-0207  of  lead  as  nitrate.     The  slight  turbidity  which 
first  takes  place  soon  goes  off,  and  the  operation  may  be 
proceeded  with   as  before.     One   cubic   centimetre  must 
naturally,  in  such  instance,  be  deducted  from  the  amount 
of  chrome  solution,  on  account  of  the  extra  addition  of 
lead. 

Bismuth  alone  seems  to  interfere  with  the  reaction, 
and  behaves  very  like  lead  with  chromic  acid,  and  if  present 
it  requires  a  different  mode  of  proceeding. 

The  higher  oxide  of  mercury  is  not  precipitated  by 
potassium  bichromate,  not  even  in  an  acetic  solution,  while 
the  lower  oxide  is ;  and,  as  it  is  difficult  to  peroxidise  all 
the  mercury  when  united  with  lead,  even  by  long-continued 
boiling  in  nitric  acid,  it  becomes  necessary  to  evaporate  and 
calcine  the  residue  till  all  the  mercury  is  volatilised.  To 
obviate  the  formation  of  red  lead,  the  calcined  residue  has 
to  be  moistened  with  a  few  drops  of  oxalic  acid,  and  again 


BUISSON'S   YOLUMETKIC   PROCESS.  475 

dried  and  carefully  calcined  and  dissolved  in  acetic  acid  ; 
after  this,  the  lead  may  be  estimated  as  usual.  To  avoid 
the  above  calcinations,  the  mercury  may  be  precipitated 
from  the  nitric  acid  solution  by  means  of  hydrochloric  acid, 
and  the  liquid  boiled  till  the  calomel  is  converted  into  the 
higher  chloride. 

Copper,  cadmium,  zinc,  iron,  and  cobalt  do  not  in  the 
least  interfere  with  the  reaction,  provided  the  iron  is  per- 
oxidised.  Of  the  different  acids,  hydrochloric  acid  some- 
what disturbs  the  last  silver  reaction,  but  by  using  larger 
drops,  and  allowing  the  reaction  of  silver  chloride  to  go 
off,  we  obtain  the  usual  silver  chromate  reaction. 

Lead  sulphate  has  first  to  be  converted  into  the  state  of 
carbonate,  by  boiling  with  sodium  carbonate,  when  it  may 
be  dissolved  in  acetic  acid.  Lead  phosphate  and  arsenite, 
or  other  lead  salts  insoluble  in  acetic  acid,  may  be  dis- 
solved in  nitric  acid,  and  estimated  according  to  my  older 
method. 


3.  BUISSON'S  VOLUMETRIC  PROCESS  FOR  ESTIMATING  LEAD. 

This  process  is  based  on  the  precipitation  of  lead  by 
potassium  bichromate  and  the  decomposition  of  the  excess 
of  the  reagent  used  by  potassium  iodide  in  a  liquid 
acidulated  with  sulphuric  acid.  0'5  to  1  gramme  of  the 
pulverised  mineral  to  be  tested  is  dissolved  in  dilute  nitric 
acid.  The  solution  is  saturated  with  potash,  and  the  preci- 
pitate redissolved  in  acetic  acid.  The  iron  is  removed  by 
boiling.  To  the  solution  separated  from  the  iron  25  c.c. 
of  potassium  bichromate  is  added,  and  water  to  bring  the 
volume  up  to  250  c.c.  After  standing  for  some  time,  the 
solution  is  filtered  through  a  dry  filter  paper.  To  100  c.c. 
of  the  clear  liquid  an  excess  of  dilute  sulphuric  acid  and 
potassium  iodide  are  added  in  such  a  way  as  to  redissolve 
the  iodine  set  free,  and  then  a  few  centimetres  of  starch. 
By  means  of  a  graduated  burette,  sodium  hyposulphite  is 
added  until  decolorisation  of  the  starch  iodide  takes  place. 
The  difference  of  standard  obtained  by  treating  the  bichro- 
mate alone,  and  after  precipitation  with  a  known  weight 


476  THE   ASSAY   OF   LEAD. 

of  lead,  gives  a  basis  for  calculating  the  amount  of  metal 
contained  in  the  substance  tested. 

Silver,  bismuth,  copper,  and  baryta  should  be  separated 
from  the  lead  before  applying  this  process. 

4.  W.  Diehl  proposes  the  following  process  for  the 
volumetrical  determination  of  lead  ('  Zeitschrift  fur  Analy- 
tische  Chemie ').  He  employs  a  -^-th  normal  solution  of 
potassium  bichromate,  containing  7*38  grms.  per  litre, 
each  c.c.  representing  0-01035  grm.  of  lead,  and  a  solution 
of  sodium  hyposulphite,  containing  4  to  5  grms.  per  litre. 
To  determine  the  relations  between  these  two  solutions, 
20  to  30  c.c.  water,  and  mixed  with  20  to  25  dilute  sul- 
phuric acid  (1  vol.  monohydrated  acid,  and  2  vols.  of 
water)  a  certain  excess  of  sulphuric  acid  is  indispensable, 
hydrochloric  acid  being  less  convenient.  The  liquid  is 
brought  to  a  boil,  and  the  solution  of  hyposulphite  is 
added  drop  by  drop.  The  solution  becomes  gradually 
paler  in  colour.  Towards  the  end,  after  the  addition  of  a 
few  drops,  it  is  let  boil  up  again.  The  end  of  the  reaction 
may  generally  be  distinguished  by  the  liquid  turning  per- 
fectly colourless,  a  result  occasioned  by  a  single  drop.  In 
order  to  judge  of  the  colour,  the  flask  towards  the  end  of 
the  operation  may  be  set  in  a  porcelain  capsule.  When 
very  large  quantities  of  bichromate  are  used  the  liquid 
does  not  become  perfectly  colourless,  but  slightly  greenish. 

In  determining  ores  in  this  manner  they  are  dissolved 
in  aqua  regia  and  dilute  sulphuric  acid,  the  solution  con 
centrated  till  the  sulphuric  acid  begins  to  evaporate, 
diluted  with  water,  boiled  to  dissolve  ferric  sulphate,  let 
cool,  and  filtered  through  a  smooth  filter,  washing  with 
water  containing  sulphuric  acid.  To  the  residue  in  the 
flask — as  little  as  possible  of  which  is  thrown  upon  the 
filter — is  added  about  15  c.c.  of  a  solution  of  neutral  am- 
monium acetate,  and  about  50  c.c.  of  water.  The  whole  is 
then  boiled,  and  filtered  through  the  same  filter,  into  which 
a  drop  of  ammonia  has  been  put,  into  a  flask.  The  same 
operation  is  then  repeated  with  5  c.c.  ammonium  acetate, 
and  the  residue  is  finally  well  washed  with  boiling  water, 
to  which  a  little  of  the  same  salt  has  been  added.  Thorough 


BUISSON'S   VOLUMETRIC    PROCESS.  477 

washing  is  necessary,  since  filters  have  been  found  to 
retain  ammonium  and  lead  acetate  and  tartrate  with  con- 
siderable obstinacy.  It  is  then  advisable  further  to  wash 
the  filter  from  its  margin  downwards  with  a  little  boiling 
dilute  hydrochloric  acid  (1  part  hydrochloric  acid  at  sp. 
gr.  1-12  with  10  parts  of  water),  and  then  to  wash  again 
with  hot  water.  In  this  manner  every  trace  of  lead  is  re- 
moved from  the  filter.  A  thin  filter  paper  should  be  used,, 
and  should  be  washed  previously.  The  solution  of  lead 
sulphate  in  ammonium  tartrate  thus  obtained  is  then 
titrated  in  the  cold  with  potassium  bichromate  ;  with  the 
aid  of  heat,  ammonium  acetate  dissolves  a  little  lead 
chromate.  The  precipitate  settles  readily  if  the  flask  is- 
shaken,  and  the  end  of  the  reaction  can  be  observed  to 
within  0-2  to  0-4  c.c. 

An  excess  of  at  least  2  c.c.  of  the  chromate  solution 
should  be  added,  in  order  to  obviate  the  solubility  of  the 
lead  salt.  It  is  advisable  in  every  experiment  to  take  as 
closely  as  possible  an  equal  quantity.  After  thoroughly 
shaking,  it  is  allowed  to  stand  for  half  an  hour  and  filtered. 
If  the  liquid  passes  through  turbid,  a  few  drops  of  a 
solution  of  sodium  acetate,  acidulated  with  acetic  acid,  are 
added.  If,  after  all,  a  little  lead  chromate  passes  through 
the  filter,  the  filtration  is  repeated.  The  precipitate  is 
washed  four  times  with  cold  water,  and  the  solution  is 
acidulated  with  sulphuric  acid  and  titrated  as  above. 

Ammonium  acetate  is  preferable  to  all  other  ammonium 
salts  as  a  solvent  for  lead  sulphate.  It  is  applied  in  a 
neutral  or  faintly  acid  state.  Free  ammonia  renders  the 
solution  turbid.  1  grm.  lead  sulphate  requires  15  c.c.  of 
the  liquid  acetate  for  solution.  Ammonium  tartrate  can- 
not be  used. 

For  the  detection  of  minute  quantities  of  lead  and 
copper  (e.g.  in  the  drainage  of  mines,  &c.),  Mr.  Pattison 
Muir  ('  Chemical  News,'  January  14,  1876)  proposes  to  use 
the  method  of  Wanklyn,  slightly  modified  (see  'Water 
Analysis,'  Trlibner  and  Co.). 


478 


CHAPTER    XII. 

THE   ASSAY   OF   TIN. 

THIS  metal  is  always  found  by  the  assayer  in  the  state  of 
oxide. 

Tin  Oxide  (Sn02). — The  appearance  of  this  mineral 
gives  no  indication,  excepting  to  an  experienced  eye,  that 
metallic  matter  enters  largely  into  its  composition  ;  yet  its 
great  density  would  lead  one  to  suppose  such  to  be  the  case. 
Its  colour  varies  from  limpid  yellowish  white  to  brownish 
black  and  opaque,  passing  from  one  to  the  other  by  all 
intermediate  shades.  It  usually  possesses  a  peculiar  kind  of 
lustre  which  cannot  be  readily  described,  but  once  seen  can 
scarcely  be  mistaken.  It  occurs  crystallised  in  square  prisms, 
terminated  by  more  or  less  complicated  pyramids.  These 
crystals,  derived  from  the  octahedron,  are  often  macled  or 
hemitropic,  so  that  they  often  possess  re-entering  angles, 
which  is  to  a  certain  extent  characteristic.  The  principal 
varieties  are  the  following  :— 

1.  Crystallised  Tin  Oxide   is    found  in  more  or  less 
voluminous  crystals  of  the  colour  and  form  as  above. 

2.  Disseminated  Tin   Oxide. — This  variety  occurs  in 
grains  of  various  sizes,  sometimes  so  small  as  not  to  be 
visible  to  the  naked  eye.     It   is  found  in  the  primitive 
rocks. 

3.  Sandy  Tin  Oxide  forms  pulverulent  masses  often  of 
great  extent ;  in  appearance  it  is  merely  a  brown  sand. 

4.  Concretionary  Tin  Oxide ,  Wood  Tin. — This  variety 
occurs  in  small  mamellated  masses,  the  fibrous  texture  of 
which  resembles  that  of  wood  ;  hence  the  name. 

The  following  is  an  analysis  of  a  sample  of  tin  oxide 
from  Cornwall : — 


OXIDE   OF   TIX.  479 

Tin    .  .        .        .        .        .        .  .  .  77-50 

Oxygen  .         .         .         .         .         .  .  .  21'40 

Iron  .  .         .         .         .         .  .  .  '25 

Silica .  .  -75 

The  following  remarks  on  tin  ore  and  the  minerals 
which  may  be  mistaken  for  it,  are  from  the  pen  of  Dr.  A. 
Leibius,  Senior  Assayer  of  the  Sydney  branch  of  the  Royal 
Mint. 

The  colour  of  native  tin  ore  varies  from  white  to  pink, 
ruby-red,  grey,  greyish-black  to  black  ;  it  therefore  is 
certainly  no  very  reliable  criterion  for  distinguishing  tin 
ore. 

A  safer  characteristic  is  the  weight,  or  specific  gravity, 
that  of  tin  ore  being  6'8  to  7*0.  Unfortunately,  however, 
the  specific  gravity  of  iron  tungstate  is  nearly  the  same 
as  that  of  tin  oxide,  in  fact,  a  little  higher,  being  7*19 
to  7*55. 

Titaniferous  iron  has  a  specific  gravity  of  from  4*5  to 
-5*0,  and  magnetic  iron  4- 9  to  5 -2. 

Basaltic  hornblende  and  iron  silicate  have  also  been 
mistaken  for  tin  ore  ;  but  the  specific  gravity  of  the  former 
being  only  3-1  to  3'4,  and  that  of  the  latter  3-8  to  4-2, 
ought  to  have  prevented  such  mistakes.  The  colour  of  the 
powdered  ore  forms  a  much  better  criterion  than  that  of 
the  unpowdered  ore.  The  powder  of  good  tin  ore  varies 
only  from  whitish-grey  to  dark  drab,  while  iron  tungstate 
powders  reddish-brown,  and  titaniferous  iron-black. 

Most  of  the  minerals  appear  to  be  mistaken  for  tin  ore 
on  account  of  their  dark  granular  pieces  having  been  taken 
for  such  ;  but  Mr.  Leibius  has  seen  a  sample,  which  con- 
sists of  blackish  pieces  with  about  50  per  cent,  of  small 
indistinct  crystals  of  a  pink  and  dark  ruby  colour,  with  a 
few  small  white  crystals.  The  whole  mixture  being  pretty 
heavy,  has  certainly  at  first  sight  all  the  appearance  of 
good  tin  ore.  Even  on  closer  inspection,  when  the  darker 
portion  just  referred  to  might  have  been  recognised  as  an 
iron  compound,  the  ruby-coloured  portion  might  readily 
pass  muster  for  tin  ore  unless  chemically  examined.  On 
further  examination  the  whole  sample  was  found  to  be 
free  from  tin.  It  was  found  to  consist — 1.  Black  portion, 


480  THE   ASSAY   OF   TIN. 

about  50  per  cent,  of  the  sample,  having  a  specific  gravity 
of  4'47,  was  found  to  be  titaniferous  iron.  2.  Kuby-coloured 
and  dark  red  pieces,  about  50  per  cent,  of  sample,  with  a 
specific  gravity  of  4'57,  found  to  be  zircons  or  hyacinths, 
snowing  the  characteristic  property,  mentioned  in  Pro- 
fessor Thompson's  excellent  '  Guide  to  Mineral  Explorers  ' 
(see  ante,  p.  288),  of  becoming  completely  and  lastingly 
colourless  when  exposed  to  heat  before  the  blowpipe, 
3.  Besides  these  zircons  were  found  a  few  small  topazes 
and  garnets,  and  also  a  small  sapphire.  The  specific 
gravity  of  the  mixed  sample  as  received  was  4 -55. 

As  already  mentioned,  there  was  actually  no  tin  in  the 
sample,  and  it  forcibly  illustrates  the  necessity  of  the 
precaution,  in  dealing  with  tin  ore,  to  have  it  carefully 
assayed. 

Assay  of  Pure  Tin  Oxide. — Pure  tin  oxide  may  be 
very  readily  assayed  in  the  following  manner  : — Weigh  off 
400  grains,  place  them  in  either  a  black-lead  or  charcoal- 
lined  crucible,  cement  on  a  cover  by  means  of  Stourbridge 
clay,  and  place  in  the  fire.  The  heat  should  for  the  first 
quarter  of  an  hour  be  a  dull  red,  after  which  it  may  be 
raised  to  a  full  bright  red  for  ten  minutes,  and  the  crucible 
removed  with  care  so  as  not  to  agitate  or  disturb  the  con- 
tents;  tapping  in  this  case  must  not  be  resorted  to.  When 
the  crucible  is  cold,  remove  the  cover,  and  a  button  of 
pure  tin  will  result ;  this  weighed  and  divided  by  four 
gives  the  percentage.  If  the  operation  has  not  been  care- 
fully conducted  it  sometimes  happens  the  tin  is  not  in  one 
button,  but  disseminated  in  globules  either  on  the  charcoal 
lining  or  on  the  sides  of  the  black-lead  pot ;  in  this  case 
the  charcoal  on  the  one  hand,  or  the  black-lead  crucible 
on  the  other,  must  be  pulverised  in  the  mortar  and  passed 
through  a  sieve ;  the  flattened  particles  of  tin  will  be  re- 
tained by  the  sieve,  and  can  be  collected  and  weighed.  If 
any  small  particles  escape  the  sieve,  they  may  be  separated 
from  the  lining  or  crucible  by  vanning. 

If  a  charcoal  or  black-lead  crucible  be  not  at  hand,  an 
ordinary  clay  pot  may  be  used,  but  not  so  successfully, 
excepting  under  -  certain  circumstances  to  be  .hereafter 


ASSAY   OF    PURE    OXIDE   OF   TIN.  481 

described.  Indeed,  in  Cornwall  the  ordinary  mode  of  con- 
ducting this  assay  is  in  a  naked  crucible,  thus  :  About  2 
ounces  of  the  ore  are  mixed  with  a  small  quantity  of 
culm,  and  projected  into  a  red-hot  crucible.  If  the  ore 
seems  to  fuse  or  work  sluggishly,  a  little  fluor-spar  is 
added,  and  after  about  a  quarter  of  an  hour's  fusing  at  a 
good  high  temperature,  the  reduced  and  fused  tin  is  poured 
into  a  small  ingot  mould,  and  the  slag  examined  for  metal 
by  pounding  and  vanning.  This  method  never  gives  the 
whole  of  the  metal.  To  effect  this,  without  fear  of  mis- 
chance in  the  assay  sometimes  occurring,  as  already  de- 
scribed with  both  blacklead  and  charcoal-lined  crucibles, 
it  may  be  thus  conducted  ;  always  supposing  the  oxide 
to  be  pure,  or  nearly  so,  or  at  least  containing  little  or 
no  siliceous  matter. 

To  400  grains  of  ore  add  100  grains  of  argol,  300  grains 
of  sodium  carbonate,  and  50  grains  of  lime;  mix  well 
together,  place  in  a  crucible  which  the  mixture  half-fills, 
cover  with  a  small  quantity  of  sodium  carbonate  and  200 
grains  of  borax.  Place  the  whole  in  the  furnace  with  the 
necessary  precautions,  raise  the  heat  very  gently,  and  keep 
it  at  or  below  a  dull  red  heat  for  at  least  twenty  minutes ; 
then  gradually  increase  until  the  whole  flows  freely.  Re- 
move the  crucible,  tap  it  as  for  copper  assay,  and  allow  to 
cool.  When  cold,  break  it,  and  a  button  of  pure  metallic 
tin  will  be  found  at  the  bottom,  and  a  flux  perfectly  free 
from  globules  and  containing  no  tin. 

There  is  yet  another  process,  which  is  more  easy  of 
execution;  but  the  reagent  employed  is  more  expensive, 
not  so  readily  obtainable,  and  more  difficult  to  keep  without 
decomposing  than  any  of  the  substances  above  employed. 
The  reagent  now  to  be  discussed  has  been  introduced  to 
the  notice  of  the  student,  in  another  part  of  this  volume, 
as  a  blowpipe  flux,  and  in  the  assay  of  copper  ores  by 
standard  solutions,  as  potassium  cyanide.  This  is  the  most 
effective  reducing  flux  for  tin  ores  yet  known.  It  acts  by 
absorbing  oxygen  to  form  a  compound  known  as  potassium 
cyanate :  thus — 

Sn02  +  KCy = Sn  +  KO,CyO. 
i  i 


482  THE    ASSAY    OF   TIN. 

The  assay,  by  means  of  this  substance,  may  be  made 
in  ten  minutes. 

This  method  of  estimating  the  value  of  tin-stone  has 
been  frequently  practised  by  the  writer,  and  has  uniformly 
furnished  correct  results  with  but  little  expenditure  of 
time  and  labour.  The  method  of  operating  is  as  fol- 
lows : — The  sample  having  been  carefully  selected,  is  first 
crushed  by  the  hammer  in  a  steel  mortar,  and  then 
further  reduced  to  powder  in  an  agate  mortar.  1 00  grains 
is  a  convenient  quantity  to  be  taken  for  analysis,  and  it 
is  always  advisable  to  make  two  independent  experiments 
upon  the  same  sample  of  ore,  with  the  view  of  having  a 
control,  and  the  highest  result  obtained  is  that  upon  which 
to  place  reliance,  since  the  error  must  always  be  on  the 
side  of  loss  rather  than  excess.  A  couple  of  small  Hessian 
crucibles,  of  about  3  oz.  capacity,  are  prepared  in  the  first 
instance  by  ramming  into  the  bottom  of  them  a  small 
charge  of  powdered  potassium  cyanide  sufficient  to  form 
a  layer  of  about  half  an  inch  in  depth  ;  the  weighed  quan- 
tities of  tin  ore  are  then  intimately  mixed  with  from  four 
to  five  times  their  weight  of  the  powdered  cyanide,  and 
the  mortar  rinsed  with  a  small  quantity  of  the  pure  flux, 
which  is  laid  upon  the  top  of  the  mixture.  The  crucibles 
are  then  heated  in  a  moderate  fire,  or  over  a  gas-blowpipe, 
and  kept  for  the  space  of  ten  minutes  at  a  steady  fusion  ; 
they  are  then  removed,  gently  tapped  to  facilitate  the 
formation  of  a  single  button,  and  allowed  to  cool.  Upon 
breaking  the  crucibles,  the  reduced  metal  should  present 
an  almost  silvery  lustre,  with  a  clean  upper  layer  of  melted 
flux.  It  is  advisable  to  dissolve  the  latter  in  water,  in  order 
to  be  certain  as  to  the  absence  of  any  trace  of  reduced  metal 
or  heavy  particles  of  the  original  ore.  There  is  always 
contained  in  the  commercial  cyanide  a  sufficient  quantity 
of  alkaline  carbonate  to  secure  the  perfect  fusion  of  the 
siliceous  gangue,  and  other  like  impurities  in  the  tin  ore, 
but  the  operator  should  assure  himself  of  the  absence  of 
copper  and  lead  in  the  ore,  either  by  preliminary  treat- 
ment with  hydrochloric  acid,  in  which  tin-stone  is  ab- 
solutely insoluble,  or  by  testing  the  button  of  reduced  tin 


ASSAY   OF   PUEE    OXIDE    OF   TIN.  483 

after  hammering  or  rolling  for  such  metallic  admixture. 
We  have  usually  found  a  minute  trace  of  iron,  and  some- 
times gold  in  the  melted  buttons,  but  not  so  much  as  to 
add  appreciably  to  their  weight. 

When  worked  with  ordinary  care,  this  process  may  be 
relied  upon  as  giving  numbers  true  to  within  -|  per  cent., 
and  we  do  not  know  any  other  method  which  exceeds  this 
in  accuracy  and  rapidity  of  execution.  The  following  are 
a  few  analytical  results  taken  at  random  from  a  number  of 
ores  assayed  in  this  manner  : — 

Tin  per  cent. 
L          ~~n. 

Sample  No.  1      V'*./.        .         .     45-6        45-8 
„      No.  2        .        .        .        .     57-2        57-6 

„      No.  3        ...  '"-...;'  .'    68-4        68-7 

Assay  of  Tin  Oxide  mixed  with  Silica. — Although  tin 
oxide  is  completely  reducible  by  charcoal  or  other  carbo- 
naceous matter,  yet  it  has  such  an  affinity  for  silica,  that 
whenever  that  substance  is  present  the  metal  cannot  be 
wholly  reduced,  excepting  at  the  highest  temperature  of  a 
wind  furnace.  The  following  experiments  will  show  the 
influence  of  silica  on  the  return  of  tin  in  an  assay  of  oxide 
of  that  metal  with  black  flux  : — 

Ore     100     100     100     100     100 
Quartz    25      66     100     150     300 

The  first  gave  52  per  cent,  of  tin ;  the  second  43  per 
cent. ;  the  third,  28  per  cent.  ;  the  fourth,  10  per  cent.  ; 
and  the  last  nothing. 

The  slags  also  produced  in  the  treatment  of  tin  ores  in 
the  large  way  give  no  return  with  black  flux.  This  mode 
of  assay,  however,  has  been  recommended  by  some,  but 
from  the  foregone  experiments  is  proved  to  be  perfectly 
fallacious  :  that  is,  unless  the  quantity  of  silica  present  be 
very  small  in  comparison  to  the  amount  of  tin  oxide  ;  and 
even  when  the  latter  is  present  in  four  times  the  quantity 
of  the  silica,  as  in  experiment  No.  1,  a  loss  of  20  per  cent 
of  tin  is  sustained. 

Assay  of  Tin  Ores  containing  Silica  and  Tin  Slags — It 
having  just  been  shown  how  injuriously  the  presence  of 
silica  influences  the  produce  of  tin,  both  in  ores  and  slags, 

n2 


484  THE   ASSAY   OF   TIN. 

other  methods  of  assay  than  those  just  described  must  be 
adopted  for  such  substances.  These  will  now  be  detailed. 

Tin  ores  containing  silica  may  be  treated  by  two 
methods  :  in  the  first  the  silica  must  be  carefully  separated 
by  vanning ;  if  the  ore  be  well  pulverised  this  is  the  best 
and  most  expeditious  method.  In  conducting  this  assay 
take  400  or  more  grains  of  the  pulverised  ore,  according 
to  its  richness  (if  poor,  as  much  as  2,000  grains  may  be 
taken),  van  it  carefully,  dry  the  enriched  product,  which 
will,  if  the  operation  has  been  properly  conducted,  be 
nearly  pure  oxide  of  tin,  and  assay  it  as  already  described 
for  ores  containing  no  silica.  The  other  process  of  assay 
may  be  thus  conducted,  and  is  dependent  upon  the  fact  that 
iron  displaces  tin  from  its  combination  with  silica :  thus, 
if  a  compound  of  tin  oxide  and  silica  be  heated  to  white- 
ness with  metallic  iron,  a  portion  of  the  iron  oxidises  and 
replaces  the  tin  oxide,  which  was  previously  in  combina- 
tion with  the  silica  as  a  tin  silicate,  and  metallic  tin  and 
iron  silicate  result,  the  tin  so  reduced  combining  with  any 
metallic  iron  that  may  be  in  excess,  and  the  button  thus 
obtained  is  an  alloy  of  tin  and  iron,  whilst  the  slag  is  en- 
tirely deprived  of  tin. 

In  this  kind  of  assay  mix  400  grains  of  the  siliceous 
tin  oxide  with  200  grains  of  iron  oxide  (either  pulverised 
haematite  or  forge-scales  will  answer  this  purpose),  100 
grains  of  pounded  fluor-spar,  and  100  grains  of  charcoal 
powder  :  place  the  mixture  in  a  crucible  and  cover  with 
a  lid,  gradually  heat  to  dull  redness,  and  keep  at  that 
temperature  for  half  an  hour,  then  heat  to  whiteness  for 
another  half-hour,  and  remove  the  crucible  from  the  fur- 
nace, allow  to  cool,  and  break.  The  button  so  obtained  is 
to  be  treated  in  the  wet  way,  as  hereafter  described. 

The  assay  of  tin  slags  is  conducted  in  the  same  manner, 
or  simply  by  mixing  the  pulverised  slag  with  20  per  cent, 
of  iron  filings,  and  fusing. 

Assay  of  Tin  Ores  containing  Arsenic,  Sulphur,  and 
Tungsten  (Wolf ram). — In  the  assay  of  such  ores  it  is  neces- 
sary to  remove  arsenic,  sulphur,  and  tungsten,  before 
attempting  to  obtain  the  tin  in  a  pure  state  by  the  dry 


ASSAY   OF   TIN   ORES    CONTAINING   ARSENIC,  ETC.  485 

assay.  Ores  of  tin  which  contain  either  one  or  all  of 
these  substances  are  most  common  :  hence  this  mode  of 
treatment  will  be  generally  required. 

Most  assay ers  usually  submit  the  ore  to  the  same  mode 
of  treatment  which  it  undergoes  on  the  large  scale  by  cal- 
cination, or  rather  roasting,  by  which  the  greater  part  of 
the  arsenical  and  pyritic  matter  is  removed ;  this  process 
fails,  however,  to  remove  the  whole  of  these  substances, 
and  does  not  at  all  affect  the  tungsten.  The  following 
process  is  therefore  preferable,  and  is  founded  on  the  fact 
that  arsenical  and  other  pyrites,  as  well  as  iron  tungstate 
(wolfram  usually  accompanying  tin  ores),  are  completely 
decomposed  by  nitro-hydrochloric  acid  (aqua  regia)  at  the 
boiling  temperature,  the  oxide  of  tin  alone  not  being 
affected  : — Take  400  grains  or  more  of  the  impure  tin 
sample,  place  them  in  a  flask,  and  add  1$  ounce  of  hydro- 
chloric acid,  and  i  an  ounce  of  nitric  acid,  heat  gently  for 
about  half  an  hour,  and  then  boil  until  the  greater  part  of 
the  mixed  acids  have  evaporated  ;  the  sulphur  and  arsenic 
will  by  this  time  be  converted  into  sulphuric  and  arsenic 
acid,  and  the  wolfram  completely  decomposed,  its  iron  and 
manganese  having  become  soluble,  and  its  tungstic  acid  re- 
maining in  the  insoluble  state  with  the  oxide  of  tin  and 
any  silica  that  may  be  present.  Allow  the  flasks  and  con- 
tents to  cool,  add  water,  allow  to  settle,  and  decant,  and  so 
on  until  the  water  passes  off*  tasteless.  The  insoluble  matter 
in  the  flask  is  now  tin  oxide,  silica,  and  tungstic  acid  ;  to 
remove  the  latter,  digest  for  an  hour  at  a  very  gentle  heat 
with  one  ounce  of  solution  of  caustic  ammonia,  with  occa- 
sional agitation ;  add  water,  and  van  the  remainder  to 
separate  silica ;  nothing  remains  now  but  tin  oxide,  with 
perhaps  a  little  silica  :  this  is  now  to  be  dried  and  assayed 
as  directed  for  ores  containing  little  or  no  silica. 

If  only  an  approximative  assay  be  needed,  it  may  be 
accomplished  after  this  treatment  by  taking  the  specific 
gravity  of  the  remaining  oxide,  so  that  all  ores  of  tin  may 
be  thus  roughly  assayed,  it  being  premised  that  the  above 
operation  has  been  so  carefully  performed  that  nothing 
but  tin  oxide  and  silica  remain.  The  specific  gravity  of 


486  THE   ASSAY   OF   TIN. 

the  thus  purified  ore  is  to  be  taken.  All  now  that  is  neces- 
sary to  be  known  is  the  specific  gravity  of  tin  oxide,  its 
percentage  of  pure  tin,  and  the  specific  gravity  of  silica, 
and  a  simple  calculation  gives  the  result.  The  following 
is  the  formula  :  — 

Let  a  represent  the  specific  gravity  of  tin  oxide. 
„    b        „  „  „  silica. 

„    c        „  „  „  the  mixture  left  after  treatment 

with  acid,  &c. 
„  w        „  weight  of  rough  tin  oxide  or  mixture  left  after 

treatment  with  acid,  &c. 
„   .r        „  „  „     tin  oxide. 

silica- 


c  (a—  6) 

b  (a—c) 

And  y  -  -)  -  Mv. 
c  (a—  6) 

Or  in  arithmetical  form  thus  — 

1.  From  the  specific  gravity  of  the  rough  tin  oxide  (mixture  of  tin  oxide 
and  silica)  deduct  the  specific  gravity  of  the  silica. 

2.  Multiply  the  remainder  by  the  specific  gravity  of  the  tin  oxide. 

3.  Multiply  the  weight  of  the  rough  tin  oxide  by  the  last  product,  which 
will  make  a  second  product,  which  may  be  called  P. 

4.  From  the  specific  gravity  of  tin  oxide  deduct  the  specific  gravity  of  silica. 

5.  Multiply  the  difference  by  the  specific  gravity  of  the  rough  tin  oxide. 

6.  Take  this  product  for  a  divisor  to  divide  the  above  product  P  :  the  quo- 
tient will  be  the  weight  of  pure  tin  oxide  in  the  rough  oxide,  and  the  quantity 
of  metal  can  now  be  readily  calculated. 

The  following  is  an  assay  worked  out  in  this  manner  :  — 

400  grains  of  the  ore  are  treated  with  nitro-hydrochloric  acid  and  ammonia 
as  above  described,  washed,  and  dried.  Suppose  the  dried  matter  weighed 
250  grains.  The  250  grains  thus  obtained  are  placed  in  the  specific  gravity 
bottle,  and  the  specific  gravity  is  found  to  be  5-4. 

Specific  gravity  of  tin  oxide  (approximate)    .         .         .     6*9 
„  silica  „  ...     2-6 

Sp.  Gr.  Sp.  Gr. 

Bough  Oxide  Silica 

5-4  2-6  =  2-8 

Sp.  Gr. 
Pure  oxide 

2-8  x  6-9  =         19-32 

Weight  of 
Rough  Oxide  P 

250  x          19-32  4830 

Sp.  Gr.  Sp.  Gr. 

Pure  oxide  Silica 

6-9  2-6  =  4-3 

Sp.  Gr. 
Rough  Oxide 

4-3  x  5-4  =         23-22 


ESTIMATION   OF   TIN    IX    THE   WET   WAY.  487 

208*4  grains  is  therefore  the  weight  of  pure  oxide  in  the  400  grains  of  ore. 
Now  tin  oxide  contains  78*61  parts  of  pure  tin,  and  a 


So  that  400  grains  of  rough  tin  ore  contain  163*72  grains  of  pure  tin,  and 


The  rough  sample  first  operated  on  contains,  therefore, 
40-93  per  cent,  of  metallic  tin. 

Another  satisfactory  method  of  assaying  tin  in  the 
presence  of  tungsten  has  been  described  by  Mr.  J.  H. 
Talbott. 

The  method  is  based  on  the  fact  already  mentioned 
that  tin  oxide  is  reduced  by  potassium  cyanide  with  great 
facility  ;  while  tungstic  acid  undergoes  no  reduction,  even 
when  heated  with  the  cyanide  at  a  high  temperature.  The 
tin  and  tungsten  oxides  are  to  be  heated  in  a  porcelain 
crucible  with  three  or  four  times  their  weight  of  commer- 
cial potassium  cyanide  previously  fused,  pulverised,  and 
thoroughly  mixed  with  the  two  oxides.  The  mass  is  kept 
fused  for  a  short  time,  when  the  tin  separates  in  the  form 
of  metallic  globules,  while  the  tungstic  acid  unites  with 
the  alkali  of  the  potassium  cyanate  and  carbonate  present. 
After  cooling,  the  mass  is  to  be  treated  with  hot  water,* 
which  dissolves  the  alkaline  tungstate  and  other  salts,  and 
leaves  the  tin  as  metal  ;  this  is  to  be  separated  by  filtra- 
tion, washed,  dried,  and  weighed  as  tin  oxide,  after  oxida- 
tion in  the  crucible  with  nitric  acid.  The  tungstic  acid 
may  be  estimated  by  difference,  or  be  precipitated  by 
mercury  protonitrate,  after  boiling  the  solution  with  nitric 
acid  to  decompose  the  excess  of  potassium  cyanide  present, 
and  then  re-dissolving  the  precipitated  tungstic  acid  by 
means  of  an  alkali. 

Estimation  of  Tin  by  the  Wet  Method.  —  There  are 
several  methods  of  effecting  this  analysis,  the  chief  diffi- 
culty being  found  in  the  intractable  nature  of  the  tin  oxide, 
it  resisting  the  action  of  all  acids.  This,  however,  may  be 
overcome  as  first  shown  by  Klaproth,  who  found  that  very 
finely  levigated  tin  oxide  was  soluble  in  hydrochloric  acid 
after  a  prolonged  fusion  with  caustic  potash  :  the  following 
is  his  process  :  — 


488  THE   ASSAY   OF   TIN. 

Fifty  grains  of  the  tin  ore,  reduced  to  the  most  minute 
state  of  division  by  levigation  or  otherwise,  is  mixed  with 
four  times  its  weight  of  caustic  potash.  The  best  mode  of 
mixing  is  to  place  the  caustic  potash  in  a  silver  crucible, 
add  its  own  weight  of  water,  and  apply  a  gentle  heat  until 
the  potash  is  dissolved  ;  then  stir  in  tin  ore,  and  gradually 
evaporate  to  dryness,  stirring  all  the  time  to  prevent  loss  by 
spirting,  as  in  the  analysis  of  iron-stone :  when  thoroughly 
dry,  enclose  the  silver  crucible  in  one  of  clay,  and  submit 
the  whole  to  a  dull  red  heat  for  at  least  half  an  hour  : 
rather  more  than  less  renders  the  perfect  solution  of  the 
tin  oxide  more  certain.  When  cold,  act  on  the  contents 
of  the  crucible  with  dilute  hydrochloric  acid,  transfer  the 
liquid  and  any  undissolved  matter  to  a  flask,  add  some 
strong  hydrochloric  acid,  and  boil  for  half  an  hour.  If  at 
the  end  of  this  time  any  of  the  tin  ore  remains  unacted  on, 
it  must  be  separated  by  decantation  or  otherwise  from  the 
solution,  dried,  again  fused  with  potash,  and  then  treated 
with  hydrochloric  acid,  in  which  it  will  now  be  found 
totally  soluble.  This  second  operation  will  not  be  needed 
if. care  has  been  taken  to  reduce  the  ore  to  the  finest 
.possible  state  of  division  at  first.  The  solution,  however 
obtained,  is  to  be  evaporated  to  dryness,  and  when  cold 
treated  with  a  small  quantity  of  hydrochloric  acid,  allowed 
to  stand  for  half  an  hour,  then  water  added,  boiled  and 
filtered  :  the  whole  of  the  tin  will  pass  through  in  solution 
as  tin  chloride,  and  any  silica  or  tungstic  acid  that  may 
be  present  will  remain  in  the  filter.  If  the  ore  contained 
copper,  lead,  and  iron,  these  metals  will  also  be  in  solution 
— at  all  events,  the  lead  partially  so  ;  but  if  the  ore  had, 
previously  to  its  fusion  with  caustic  potash,  been  treated 
with  aqua  regia,  as  already  described,  then  it  will  contain 
tin  alone.  It  is  always  better  thus  to  separate  foreign 
matters  before  attempting  the  solution  of  the  tin,  as  the 
after  process  is  thereby  simplified.  Supposing,  however, 
that  the  rough  ore  had  been  submitted  to  fusion  with 
potash  and  then  dissolved,  the  solution  must  be  treated 
thus : — A  bar  of  zinc  must  be  placed  in  the  solution, 
which  will  in  course  of  time  precipitate  tin,  copper,  and 


ESTIMATION    OF   TIN   IN   THE   WET  WAY.  489 

lead  ;  when  all  the  metals  are  thus  thrown  down  the  zinc 
is  washed  and  removed,  the  precipitated  metals  well 
washed  and  dried.  To  the  dried  metals  strong  nitric  acid 
is  now  to  be  added,  the  mass  gently  heated,  and  then 
evaporated  to  dryness  :  when  cold,  it  is  moistened  with 
dilute  nitric  acid,  water  added,  and  the  whole  filtered. 
Lead  and  copper  will  pass  through  the  filter  as  soluble 
nitrates,  and  the  tin  will  be  found  in  the  filter  as  insoluble 
peroxide ;  this  is  to  be  well  washed,  dried,  ignited,  and 
weighed.  It  contains  78'61  parts  of  metallic  tin.  The 
amount  of  tin  thus  obtained,  when  multiplied  by  two,  will 
represent  the  percentage  of  the  ore. 

If,  before  the  action  of  caustic  potash,  the  ore  had 
been  submitted  to  the  action  of  aqua  regia,  sulphuretted 
hydrogen  may  be  passed  through  the  solution  of  tin  chlo- 
ride, wThen  tin  sulphide  will  be  precipitated  ;  this  is  to  be 
washed,  dried,  gently  calcined  in  a  platinum  crucible 
until  all  smell  of  sulphurous  acid  has  ceased,  allowed  to 
cool,  reheated  with  a  fragment  of  ammonium  carbonate, 
as  in  the  case  of  roasting  copper  sulphide,  and  when  cold 
weighed  as  pure  oxide  of  tin.  The  calculation  for  metal 
is  made  as  above. 

Mr.  J.  W.  B.  Hallet  has  found  that  tin-stone  is  very 
easily  resolved  by  fusion  with  three  or  four  times  its 
weight  of  potassium  fluoride.  The  mineral  must  be  finely 
pulverised.  The  fused  mass  is  treated  directly  in  the  cru- 
cible with  sulphuric  acid  to  expel  fluorine,  after  which, 
by  adding  water,  filtering,  and  boiling  the  filtrate,  the  whole 
of  the  tin  is  thrown  down  as  stannic  acid,  which  is  to  be 
separated  from  traces  of  iron  in  the  usual  manner.  This 
method  of  resolving  the  ore  of  tin  is  much  more  convenient 
than  fusion  with  caustic  alkalies,  or  with  sulphur  and  car- 
bonate of  sodium. 

M.  Moissenet  precipitates  the  metal  from  a  solution  of 
the  chloride  by  means  of  zinc,  and  then  melts  the  precipi- 
tated metal  in  stearic  acid.  His  process  comprises  five 
operations  : — 

1.  Purification  of  the  ore  by  treatment  with  aqua  regia. 

2.  Eeduction  of  the  residue  in  the  presence  of  charcoal. 


490  THE   ASSAY   OF   TIN. 

3.  Solution  of  the  tin  and  iron  in  hydrochloric  acid. 

4.  Precipitation  of  the  tin  by  means  of  zinc. 

5.  Fusion  of  the  precipitate  into  a  button  in  stearic 
acid. 

The  precipitation  of  tin  by  zinc  is  very  rapid,  and  takes 
place  in  strongly  acid  solutions  :  but  the  amount  of  acid  and 
the  dilution  of  the  chloride  influence  the  condition  of  the 
precipitate.  In  some  solutions  it  appears  in  brilliant 
needles,  but  in  very  dilute  solutions,  and  always  towards 
the  end  of  an  operation,  it  is  only  a  muddy  deposit.  The 
author  recommends  that  a  button  of  zinc  be  suspended  in 
the  liquid  by  means  of  a  copper  wire.  When  the  precipita- 
tion is  finished,  the  metal  is  collected  and  pressed  into  a 
porcelain  capsule.  The  lump  so  formed  is  melted  in  a  few 
minutes  if  a  piece  of  stearine  is  added  to  it. 

Assay  of  Tin  in  Gun-  and  Bell-Metal. — The  following 
process  has  been  employed  for  some  years  in  H.  Sainte- 
Claire  Deville's  laboratory : — Dissolve  about  5  grms.  of  the 
alloy  in  strong  nitric  acid  contained  in  a  flask  provided 
with  a  funnel  in  the  neck  to  prevent  loss  by  spirting. 
When  quite  dissolved  boil  the  strong  solution  for  about 
twenty  minutes ;  dilute  with  two  or  three  times  its  bulk 
of  water  and  boil  again  for  the  same  time.  Separate  the 
insoluble  tin  oxide  by  decantation,  or  filtration,  and  weigh 
after  calcining  it.  (The  tin  oxide  is  sometimes  rose- 
coloured,  owing  to  the  presence  of  minute  traces  of  gold  ; 
this  may  be  disregarded.)  The  nitric  acid  solution  freed 
from  the  tin  is  evaporated  on  a  small  platinum  or  porce- 
lain dish,  and  the  residue  is  calcined  at  a  dull  red  heat. 
In  this  manner  a  mixture  of  oxides  is  obtained  in  a  suf- 
ficient quantity  to  suffice  for  at  least  two  analyses. 

About  2  grms.  of  the  finely  pulverised  oxides  are 
placed  in  a  small  platinum  or  porcelain  boat,  and  thence 
introduced  into  a  small  glass  tube  closed  with  a  good  cork 
suitable  for  weighing.  The  boat,  the  tube,  and  the  cork 
having  been  previously  weighed,  the  weight  of  the  oxides 
is  obtained  after  they  have  been  heated  to  dull  redness  in 
the  apparatus,  through  which  a  current  of  dry  air  circu- 
lates. After  having  weighed  the  whole,  the  current  of  air 


ASSAY   OF   TIN    IN   GUN-    AND   BELL -METAL.  491 

is  replaced  by  dry  hydrogen,  and  the  tube  is  heated  over 
a  lamp  until  the  contents  cease  to  lose  weight.  It  then 
contains  unreduced  zinc  oxide  together  with  copper,  lead, 
and  iron  in  the  metallic  state ;  the  colour  of  the  product 
shows  the  operator  when  the  experiment  is  concluded.  On 
weighing  again  the  loss  of  weight  indicates  with  great 
accuracy  the  amount  of  oxygen  contained  in  the  oxides  of 
these  three  metals. 

If  the  iron  and  lead  are  present  in  inappreciable  quan- 
tities, by  multiplying  this  loss  by  5  will  be  given  very 
nearly  the  weight  of  copper  present,  and,  in  consequence, 
the  composition  of  the  alloy  itself. 

For  bronze,  bell-metal,  gun-metal,  etc.,  E.  Burse 
(' Zeitschrift  flir  Analytische  Chemie,'  1878,  p.  58)  pro- 
ceeds as  follows  :  1  grm.  of  the  alloy,  cut  in  pieces,  is 
placed  in  a  beaker,  covered  with  6  c.c.  nitric  acid,  of  sp. 
gr.  1*5  :  3  c.c.  water  are  then  slowly  poured  in  and  the 
beaker  quickly  covered.  When  the  whole  is  dissolved  it 
is  heated  to  a  boil  and  diluted  with  500  c.c.  boiling  water. 
The  tin  oxide,  after  it  is  completely  settled,  is  washed  with 
boiling  water,  and  weighed.  The  filtrate,  for  the  expul- 
sion of  nitric  acid  is  evaporated  with  two  grms.  sulphuric 
acid,  and  the  copper,  with  the  addition  of  sulphurous  acid, 
is  precipitated  with  a  solution  of  2  grm.  ammonium  sulpho- 
cyanide.  The  copper  sulphocyanide,  after  settling,  wash- 
ing, and  drying,  is  weighed  as  such,  or  is  converted  into 
sulphide.  The  filtrate  is  concentrated  with  the  addition 
of  nitric  acid,  and  mixed  with  ammonia  in  excess.  If 
iron  oxide  is  deposited  it  is  filtered  off  and  weighed.  The 
ammoniacal  solution  of  zinc  is  mixed  with  ammonium 
sulphide,  avoiding  excess,  the  sulphide  when  deposited  is 
filtered  off,  dried,  and,  after  ignition  with  sulphur  in  a 
current  of  hydrogen,  weighed. 

Estimation  of  Tin  by  means  of  a  Standard  Solution. — 
The  first  process  to  be  described  is  due  to  M.  Gaultier  de 
Claubry,  and  may  be  thus  performed  :  The  standard  solu- 
tion is  made  by  dissolving  100  grains  of  iodine  in  1  quart 
of  proof  spirit  (spirit  of  wine  having  a  specific  gravity  of 
*920),  and  is  thus  standardised.  Ten  grains  of  pure  tin  are 


492  THE   ASSAY    OF    TIK 

dissolved  in  excess  of  hydrochloric  acid,  the  solution 
boiled,  and  allowed  to  cool :  the  burette  is  now  filled  with 
the  solution  of  iodine,  which  is  gradually  added  to  that  of 
the  tin  until  the  former  ceases  to  be  decolorised  ;  as  soon, 
therefore,  as  the  tin  solution  assumes  a  faint  yellow  tinge, 
sufficient  iodine  has  been  added  ;  the  quantity  thus  found 
sufficient  is  then  noted,  and  the  amount  of  tin  each  divi- 
sion of  iodine  solution  is  equivalent  to,  is  calculated  as 
for  iron,  copper,  and  the  other  standard  solutions. 

In  the  actual  assay  of  tin  ore  by  means  of  this  solution 
it  is  necessary  that  the  whole  of  the  tin  present  be  reduced 
to  the  state  of  protochloride  :  this  may  be  readily  effected 
by  boiling  the  solution  of  tin  for  a  quarter  of  an  hour  with 
excess  of  metallic  iron,  and  filtering.  To  the  solution  so 
obtained  the  iodine  is  added  as  above.  The  tin  ore  is  dis- 
solved by  any  of  the  methods  already  described. 

M.  Lenssen  *  estimates  tin  by  means  of  the  iodine 
solution,  but  he  operates  in  a  liquid  containing  double 
potassium  and  sodium  tartrate,  and  sodium  bicarbonate  in 
excess.  The  results  M.  Lenssen  obtained  by  this  method 
are  satisfactory,  by  using  the  atomic  weight  of  tin  gener- 
ally adopted  (59).  We  shall  see  farther  on  why  M. 
Lenssen's  results  agree. 

M.  Stromeyer  f  having  recently  occupied  himself  with 
the  same  subject,  has  succeeded  in  solving  the  difficulty. 
The  solution  of  stannous  chloride  is  carefully  introduced 
into  an  excess  of  ferric  chloride.  The  salt  of  iron  becomes 
reduced  to  a  minimum,  according  to  the  following  equa- 
tion : — 

2Sn  +  2(Fe2Cl6)  =  2SnCl2  +  4FeCl2. 

It  is  then  estimated  by  permanganate,  as  if  it  were  a 
salt  of  iron  protoxide.  The  results  M.  Stromeyer  obtains 
in  this  way  are  very  exact.  The  author  adds  that  such  a 
method  of  estimating  is  applicable  only  in  the  absence  of 
copper  or  iron,  as  these  two  metals  decompose  potassium 
permanganate  as  well  as  the  tin  ;  but  it  may  be  of  great 
use  in  the  estimation  of  commercial  salts  of  tin. 

*  '  Annalen  der  Ohemie  und  Pharmacie/  vol.  cxiv.  p.  114. 
t  Ibid.  vol.  cxvii.  p.  261. 


ESTIMATION    OF   TIN    BY   A    STANDARD    SOLUTION.  493 

A  method  for  the  analysis  of  tin  ore  consists  in  reduc- 
ing the  finely-powdered  ore,  in  a  hand  porcelain  vessel,  in 
a  current  of  hydrogen  gas.  A  bright  red  heat  must  be 
applied  and  maintained  for  a  considerable  time.  The 
sample  is  allowed  to  cool  in  a  current  of  hydrogen  and 
weighed,  the  operation  being  preferably  repeated  to  make 
sure  that  the  reduction  is  complete.  The  loss  of  weight 
gives  the  quantity  of  stannic  acid,  tin  peroxide  (1  part 
by  weight  of  oxygen  representing  4- 67 3  parts  tin  per- 
oxide), if  no  other  oxide  is  present  which  may  be  reduced 
at  the  same  time.  But  as  tin-stone  contains  almost  always 
iron  oxide,  part  of  the  loss  is  due  to  this  compound,  so 
that  the  crucible,  with  its  contents,  should  be  digested  in 
a  beaker  with  hydrochloric  acid.  When  dissolved,  it  is 
diluted,  filtered  into  a  large  flask,  the  quantity  of  the 
residue  (silica,  etc.)  determined,  the  liquid  supersatu- 
rated with  ammonia,  a  sufficient  quantity  of  ammonium 
sulphide  added  with  flowers  of  sulphur,  so  as  to  convert 
the  stannous  sulphide  into  stannic  sulphide,  which  then 
dissolves  in  the  ammonium  sulphide.  The  whole  is  di- 
gested in  the  flask,  loosely  stoppered,  till  the  black  iron 
sulphide  is  separated  from  the  yellow  liquid,  filtered  under 
cover,  washed  with  the  addition  of  a  little  ammonium 
sulphide,  dissolved  in  hydrochloric  acid,  oxidised  with 
potassium  chlorate,  and  the  ferric  oxide  (iron  peroxide) 
precipitated  with  ammonia.  The  tin  may  be  directly  de- 
termined by  precipitating  the  solution  of  sulphide  with 
dilute  sulphuric  acid,  using  a  slight  excess.  The  vessel  is 
loosely  covered  with  paper,  and  very  gently  heated,  till  it 
no  longer  smells  of  sulphuretted  hydrogen.  The  yellow 
tin  sulphide  is  washed  upon  the  filter,  dried  enough  to 
enable  it  to  be  taken  out  of  the  funnel  along  with  the 
paper,  and  heated  very  gently,  for  a  considerable  time, 
in  a  porcelain  crucible,  at  first  covered  and  then  open. 
When  the  odour  of  sulphurous  acid  is  no  longer  percep- 
tible, the  contents  of  the  funnel  are  moistened  with  a  few 
drops  of  nitric  acid,  and  are  then  gradually  heated,  with 
excess  of  air,  ultimately  to  full  redness.  The  tin  sulphide 
is  thus  converted  into  stannic  acid,  which  is  heated  for  a 


494  THE   ASSAY   OF   TIN. 

short  time  with  a  little  ammonium  carbonate  to  remove 
every  trace  of  sulphuric  acid. 

In  another  method  for  the  assay  of  tin-stone,  the 
finely-ground  sample  is  mixed  in  a  porcelain  crucible 
with  3  parts  sodium  carbonate,  and  3  parts  of  sulphur, 
and  the  mixture  is  melted — covered — over  the  lamp. 
When  cold,  the  crucible  is  laid  in  water,  and  heat  is 
applied  till  the  mass  dissolves,  iron  or  other  electro- 
positive metals  remaining  as  a  black  sulphide,  which  is 
filtered  off,  washed,  and  when  dry  ignited  in  the  air,  in 
order  to  convert  it  into  iron  oxide.  From  the  dilute 
alkaline  solution  the  tin  sulphide  is  precipitated  by  dilute 
sulphuric  acid,  as  directed  above. 

In  case  of  impure  tin  ores,  the  insoluble  sulphide  may 
consist  of  iron,  zinc,  copper,  and  bismuth  ;  whilst  the  solu- 
ble, along  with  the  tin,  may  contain  arsenic,  tungsten,  and 
molybdenum.  A  process  for  the  separation  of  tin  from 
tungsten  has  been  given  at  p.  487. 

Tin  slags  are  decomposed  by  means  of  aqua  regia,  and 
the  tin,  etc.,  precipitated  by  a  current  of  sulphuretted 
hydrogen. 

Tin  furnace  products  may  be  in  part  alloys  of  tin  and 
iron,  lead,  tungsten,  cobalt,  and  arsenic.  They  are  finely 
powdered,  digested  with  aqua  regia,  the  tin  thrown  down 
with  sulphuretted  hydrogen,  and  the  tin  sulphide  treated 
as  already  directed.  If  the  proportion  of  tungstic  acid  is 
considerable,  after  digestion  in  aqua  regia  and  diluting,  the 
tungstic  acid  separates  along  with  some  stannic  acid.  This 
deposit  is  filtered  off,  washed,  dried,  and  repeatedly  ignited 
with  sal-ammoniac,  in  a  covered  porcelain  crucible,  till 
the  weight  of  the  residual  tungstic  acid  is  constant.  The 
stannic  acid  is  found  as  difference.  Sulphuretted  hydro- 
gen is  then  passed  into  the  acid  solution  (from  which  the 
tungstic  acid  has  been  deposited) ;  the  remaining  tin  is 
thus  precipitated  as  sulphide,  and  is  filtered  off.  Iron 
and  manganese  are  determined  in  the  filtrate.  (F.  Ram- 
melsberg's  Quant.  Chem.  Analyses.) 

We  have  seen  that  M.  Stromeyer,  by  a  happy  modifi- 


ESTIMATION   OF   TIN    BY   A   STANDARD  SOLUTION.  495 

cation,  has  reduced  the  estimation  of  tin  to  that  of  iron. 
Applying  the  same  principle,  a  salt  of  copper  may  be 
substituted  for  a  salt  of  iron.  An  equivalent  quantity 
of  copper  can  thus  be  estimated  in  place  of  tin  ;  and 
M.  Mohr's  as  well  as  M.  Terreil's  *  experiments  show  that 
copper  can  be  very  exactly  estimated  by  permanganate  of 
potash. 

A  double  decomposition  takes  place  on  protochloride 
of  tin  being  added  to  nitrate  or  chloride  of  copper  in 
excess ;  a  salt  of  suboxide  of  copper  forms,  and  the  tin 
passes  to  the  maximum  state  of  oxidation,  according  to 
the  following  equation  : — 

4CuO  +  2SnCl2  =  2Cu20  +  SnCl4  +  Sn02. 

To  estimate  tin  it  is,  then,  sufficient  to  transform  it 
into  protochloride,  to  add  to  it  a  solution  of  nitrate  of 
copper  slightly  in  excess,  before  diluting  it  with  water, 
and  to  titrate  the  liquid  obtained  by  permanganate  of 
potash. 

There  are  then  three  different  processes  for  estimating 
tin  by  potassium  permanganate  : — 1.  To  operate  with 
water  freed  from  air  by  boiling,  protecting  it  from  access 
of  air  while  cooling.  2.  To  oxidise  protoxide  of  tin  in 
an  alkaline  medium.  3.  To  decompose  stannous  chloride 
either  by  a  salt  of  iron,  as  proposed  by  M.  Stromeyer,  or 
by  a  salt  of  copper. 

Alloys  of  tin  and  lead,  such  as  solder,  inferior  tinfoil, 
and  the  coating  of  terne  plates,  may  be  treated  thus, 
according  to  Eammelsberg  : — 

Oxidise  with  nitric  acid ;  evaporate  to  dryness  in  the 
water-bath  ;  heat  the  residue  rather  more  strongly ; 
moisten  with  nitric  acid  when  cold ;  dilute  and  separate 
the  stannic  acid  (tin  peroxide)  by  nitration,  washing  till 
the  nitrate  has  no  longer  an  acid  reaction.  When  dry 
the  precipitate  is  detached  from  the  filter,  and  placed  in 
a  porcelain  crucible  ;  the  paper  is  burnt  on  the  lid.  the 

*  Comptes-Rendus,  vol.  xlvi.  p.  230. 


496  THE    ASSAY    OF    TIN. 

ash  added  to  the  contents  of  the  crucible,  moistened  with 
a  few  drops  of  nitric  acid,  heated,  and  finally  ignited. 
The  tin  is  calculated  from  the  stannic  acid. 

In  the  filtrate  the  lead  is  determined  as  sulphate  by 
the  addition  of  sulphuric  acid.  (See  'Separation  of  Lead 
from  Copper  and  Zinc.') 


497 


CHAPTER  XHI. 

THE    ASSAY    OF    ANTIMONY. 

AXTIMOXIAL  substances  susceptible  of  being  assayed  by  the 
dry  way  are  divisible  into  two  classes. 

CLASS  I.  In  this  class  are  comprised  native  antimony 
and  all  antimonial  substances  containing  oxygen  or  chlorine, 
and  but  little  or  no  sulphur. 

These  substances  are  the  following  :  — 

Native  antimony,  Sb, 
Antimony  oxide,  Sb2O3, 
Antimonious  acid,  Sb204, 
Antimonic  acid,  Sb203. 

CLASS  II.  includes  antimony  sulphide  and  all  antimo- 
nial ores  containing  much  sulphur. 

Antimony  sulphide,  Sb2Ss, 

Antimony  oxysulphide,  Sb203  +  2Sb2Ss, 

Haidingerite/2Sb2S3 


ASSAY   OF    ORES   OF   THE   FIRST   CLASS. 

All  antimony  oxides  are  very  readily  reduced  by  char- 
coal ;  so  that  their  assay  presents  no  difficulty.  The  assay 
is  conducted  in  precisely  the  same  manner  as  that  of  lead 
oxide  ;  only,  as  antimony  is  much  more  volatile  than  lead, 
the  heat  must  be  managed  with  care,  and  the  assay  taken 
from  the  fire  as  soon  as  finished.  When  all  suitable  pre- 
cautions are  taken,  the  loss  of  antimony  is  not  very  con- 
siderable ;  but  Berthier  says  it  is  never  less  than  from  5 
to  6  per  cent.  This,  we  think,  is  too  high.  Thus  the 
pure  protoxide  gives  77  per  cent,  of  metal,  and  antimo- 

E:  K 


498  THE   ASSAY   OF   ANTIMONY. 

nious  acid  75.  The  reduction  is  readily  made,  without 
addition,  in  a  charcoal  crucible  ;  but  when  the  substance 
to  be  assayed  is  mixed  with  impurities,  some  flux  must  be 
added.  It  succeeds  equally  well  with  3  parts  of  black 
flux,  with  1  part  of  tartar,  with  1  part  of  sodium  carbo- 
nate, and  15  per  cent,  of  charcoal,  or  any  other  equivalent 
reducing  flux. 

When  the  substance  under  assay  contains  iron  oxide, 
the  latter  oxide  is  more  or  less  reduced,  and  the  metallic 
iron  alloys  with  the  antimony. 

Oxidised  minerals  which  contain  but  a  small  quantity 
of  sulphur  can  also  be  assayed  in  this  manner  ;  because 
the  sulphide  gives  up  to  black  flux  the  small  quantity  of 
antimony  which  it  contains,  so  that  but  little  remains  in 
the  slag.  The  common  glass  of  antimony  produces  by 
this  method  of  assay  70  per  cent,  of  antimony,  and  occa- 
sionally even  more  than  that. 

The  ores  of  this  class  occur  very  seldom,  and  are  only 
in  rare  cases  subject  to  assaying. 


ASSAY   OF   ORES   OF   THE   SECOND    CLASS. 

As  pure  antimony  sulphide  (antimonium  crudum)  as 
well  as  metallic  antimony  (regulus  of  antimony)  are  mer- 
cantile substances,  the  assays  of  the  ores  of  this  class  have 
for  their  object  the  determination  of  both  these  bodies. 


1.  ASSAY  OF  PURE  ANTIMONY  SULPHIDE  (ANTIMONIUM 
CRUDUM). 

Antimony  sulphide  is  almost  the  only  mineral  from 
which  antimonium  crudum  is  produced.  This  mineral 
generally  occurs  intermixed  with  very  refractory  gangue 
(gneiss,  quartz,  limestone,  etc.).  Antimony  sulphide  fuses 
readily  at  a  low  red  heat,  and  is  not  changed  during 
fusion,  if  atmospheric  air  is  precluded.  At  a  white  heat  it 
volatilises  without  change  of  composition. 

The  assay  of  antimony  sulphide  is  now  effected  by  a 


ASSAY   OF   KEGULUS    OF   ANTIMONY.  499 

liquation  process,  i.e.  by  heating  the  mineral  sufficiently  in 
order  to  melt  the  antimony  sulphide,  and,  by  this  means, 
to  separate  it  from  the  refractory  gangue.  The  produc- 
tion of  antimony  sulphide  on  a  large  scale  is  done  in  the 
same  way. 

For  the  purpose  of  assaying,  two  pots  or  crucibles  are 
used,  one  standing  in  the  other,  and  leaving  sufficient 
space  between  the  two  to  receive  the  fused  antimony 
sulphide.  The  bottom  of  the  inside  crucible  is  furnished 
with  holes.  The  mineral  to  be  assayed  is  put  into  the 
inside  crucible,  the  latter  is  then  closed  with  a  cover,  and 
hermetically  luted  ;  the  joints  of  the  two  crucibles  are 
also  luted.  The  under  crucible  is  then  put  on  the  hearth 
of  a  furnace,  enclosed  with  ashes  or  sand,  in  order  to  keep 
it  cool,  and  the  upper  crucible,  as  far  as  it  is  outside  of 
the  under  crucible,  is  covered  with  coal,  and  heated  to  a 
moderate  red  heat.  The  antimony  sulphide  will  then 
melt  and  collect  in  the  under  crucible,  from  which  it  may 
be  taken. out,  after  cooling,  and  weighed. 

2.  ASSAY  OF  KEGULUS  OF  AJTTIMONY. 

This  assay  may  be  made  in  two  ways  :  first,  by  roast- 
ing and  fusing  the  oxidised  matter  with  black  flux  ; 
secondly,  by  fusing  the  crude  ore  with  iron,  or  iron 
scales,  with  or  without  the  addition  of  black  flux. 

The  roasting  of  antimony  sulphide  requires  much 
care,  for  it  is  very  fusible  and  volatile,  as  is  also  the  oxide 
its  decomposition  gives  rise  to.  The  heat  ought  to  be 
very  low  during  the  operation,  and  the  substance  con- 
tinually stirred.  When  no  more  sulphurous  acid  is  given 
off,  we  may  feel  assured  that  it  is  perfectly  roasted, 
because  no  sulphate  is  ever  formed  in  this  operation. 

The  roasted  sulphide  is  then  fused  with  three  parts  of 
black  flux,  or  its  equivalent. 

Metallic  iron  very  readily  separates  all  the  sulphur 
from  antimony  sulphide ;  but  as  iron  sulphide  has  a 
specific  gravity  near  that  of  antimony,  the  separation  is 
very  difficult  to  manage  :  a  strong  fire  must  be  employed 

K   K   2 


500  THE   ASSAY   OF   ANTIMONY. 

when  the  desulphurisation  is  complete,  to  keep  the  whole 
body  in  full  fusion,  for  a  considerable  time.  With  these 
precautions,  two  buttons  are  obtained,  which  separate  very 
well :  the  one  white,  and  in  large  plates,  which  is  anti- 
mony ;  and  the  other  a  bronze  yellow,  a  little  brighter 
than  the  ordinary  iron  sulphide,  because  it  is  mixed  with 
a  little  metallic  antimony.  During  the  operation  a  con- 
siderable portion  of  antimony  is  always  volatilised,  which, 
by  this  process,  is  an  inconvenience  impossible  to  avoid. 

It  is,  nevertheless,  practised  in  the  large  way  in  some 
factories  ;  but  a  good  result  is  not  generally  obtained.  It, 
however,  appears  that  when  all  the  necessary  precautions 
are  taken,  it  can  be  employed  with  advantage. 

The  first  precaution  which  is  indispensable  is,  mixing 
with  the  sulphide  only  the  precise  proportion  of  iron 
necessary  to  effect  its  decomposition,  which  quantity 
amounts  to  about  42  per  cent,  of  its  weight.  If  more  be 
used,  the  antimony,  having  a  great  tendency  to  play  the 
part  of  an  electro-negative  element,  will  combinei  with  the 
surplus,  and  an  iron  antimonide  results,  part  of  which  will 
remain  in  the  antimony  and  part  in  the  slag. 

Further,  the  iron  ought  to  be  in  the  finest  possible 
state  of  division.  If  the  masses  be  large,  a  portion  of 
antimony  sulphide  is  volatilised  before  they  can  be  fully 
attacked.  In  general,  63  per  cent,  of  antimony  can  be 
extracted  from  sulphide  by  the  aid  of  iron  in  the  small 
way,  but  on  the  large  scale  it  seems  that  55  per  cent,  is 
the  maximum. 

Cast  iron  cannot  be  employed  instead  of  wrought, 
because  sulphur  has  very  little  action  on  it.  The  desul- 
phurisation is  imperfect,  and  the  slag  adheres  to  the 
reduced  metal. 

One  of  the  greatest  inconveniences  in  separating 
sulphur  from  antimony  by  means  of  iron  is  the  strong 
heat  necessary  to  separate  the  slag  from  the  metal.  This 
might  be  remedied  by  making  the  slag  more  fusible  and 
less  heavy,  by  the  addition  of  some  flux,  as  an  alkaline 
carbonate  or  sulphate. 


ASSAY   OF   KEGULUS   OF   ANTIMONY.  501 

If  antimony  sulphide  be  fused  with  an  alkaline  car- 
bonate and  charcoal,  a  regulus  is  obtained,  and  a  slag  com- 
posed of  an  alkaline  sulphide  and  antimony  sulphide.  If 
metallic  iron  be  thrown  into  this  slag  whilst  in  fusion,  all 
the  antimony  separates  immediately,  and  a  new  slag  is 
formed  as  fluid  as  the  former,  containing  iron  sulphide 
and  a  sulphide  of  the  alkaline  base  employed.  If,  instead 
of  the  above  process,  the  iron  be  mixed  intimately  with 
the  antimony  sulphide  and  carbonated  alkali,  the  result  is 
the  same — 100  parts  of  sulphide,  42  of  metallic  iron,  50  of 
sodium  carbonate  mixed  with  one-tenth  of  its  weight  of 
charcoal,  or  50  of  black  flux,  give  65  to  66  of  regulus ; 
with  the  same  proportion  of  iron,  and  only  10  of  flux, 
only  62  per  cent,  can  be  obtained.  In  these  two  cases  the 
fusion  takes  place  very  rapidly  and  without  bubbling,  and 
the  slag,  which  is  very  liquid,  separates  readily  from 
the  metal.  By  employing  1  part  of  alkaline  flux,  the 
proportion  of  iron  can  be  reduced  from  25  to  30  per  cent,, 
and  the  product  of  metal  is-  always  from  65  to  66  per 
cent. 

Hence,  in  making  an  assay  of  antimony  sulphide,  it  is 
always  better  to  employ  a  smaller  quantity  of  iron  than  is 
necessary  to  complete  the  desulphurisation,  and  make 
up  for  it  by  increasing  the  quantity  of  flux  :  then  it  may 
be  ensured  that  no  excess  of  iron  will  be  present. 

The  alkaline  sulphates  are  decomposed  into  alkaline 
sulphides  by  the  agency  of  charcoal  at  a  slightly  elevated 
temperature.  The  sulphides  of  the  alkaline  metals,  by 
combining  with  the  other  metallic  sulphides,  augment 
their  fusibility  very  considerably.  Thus  when  sodium 
sulphate,  mixed  with  about  one-fifth  of  its  weight  of 
charcoal,  is  added  to  a  mixture  of  antimony  sulphide 
and  metallic  iron,  the  metallic  antimony  separates  very 
rapidly,  and  the  slag  almost  instantly  becomes  perfectly 
fluid. 

But  it  must  be  noted  that  the  presence  of  an  alkaline 
sulphide  diminishes  the  product  of  regulus,  unless  the 
proportion  of  iron  be  augmented  at  the  same  time. 


502  THE   ASSAY   OF   ANTIMONY. 

For  instance,  with 

100  parts  of  antimony  sulphide, 

42  parts  of  iron, 
100  parts  of  sodium  sulphate, 

20  parts  of  charcoal, 

but  22  parts  of  regulus  were  furnished  ;  but  with 

100  parts  of  antimony  sulphide, 
42  parts  of  iron, 
10  parts  of  sodium  sulphate, 
2  parts  of  charcoal, 

62  parts  of  antimony  were  easily  obtained. 

Instead  of  metallic  iron,  pure  iron  oxide  may  be  used, 
or  any  ferruginous  matter  whatever,  provided  it  is  rich  ; 
but  it  is  necessary  to  add,  at  the  same  time,  an  alkaline 
flux  and  charcoal  to  reduce  the  iron  oxide, 

Not  less  than  40  parts  of  iron  scales  can  be  employed 
for  100  of  antimony  sulphide,  and  then,  on  the  addition 
of  50  to  100  parts  of  sodium  carbonate  and  8  to  10  of 
charcoal,  about  56  of  regulus  are  obtained  ;  but  if  with 
100  parts  of  sodium  carbonate  from  14  to  15  parts  of 
charcoal  be  employed,  65  parts  of  antimony  are  the  result. 
By  augmenting  the  proportion  of  scales,  that  of  soda  may 
be  diminished.  Thus,  if  from  56  to  60  parts  of  scales,  10 
of  soda,  and  10  of  charcoal  be  employed,  50  parts  of 
regulus  are  the  result ;  and  if  the  proportion  of  soda  be 
50,  and  that  of  carbon  10,  from  65  to  66,  and  even  67, 
parts  of  regulus  are  obtainable. 

The  fusion  always  takes  place  quickly,  and  the  slags 
are  very  fluid. 

When  antimony  sulphide  is  fused  with  forge  slag 
(ferrous  silicate),  sodium  carbonate,  and  charcoal,  a  very 
white  crystalline  regulus,  in  ]arge  plates,  is  obtained  ; 
together  with  a  bronze-yellow  matt,  and  a  black, 
opaque,  vitreous  slag,  shining  like  jet,  in  which  the 
greatest  portion  of  the  alkali  employed  appeared  to  be 
concentrated. 


.       ASSAY   OF   REGULUS   OF   ANTIMONY.  503 

These  three  substances  separate  very  readily  from  each 
other. 

100  parts  of  antimony  sulphide, 
80  parts  of  forge  slag, 
50  parts  of  sodium  carbonate, 
10  parts  of  charcoal, 

produced  very  readily  60  parts  of  regulus. 

Antimony  sulphide  may  also  be  analysed  by  boiling 
with  aqua  regia.  The  residue  consists  of  sulphur  and 
gangue.  It  is  to  be  washed  and  dried,  then  weighed  and 
ignited.  The  loss  will  be  sulphur,  and  the  remainder  is 
pure  gangue. 

Water  is  then  added  to  the  filtered  solution,  which  will 
cause  the  precipitation  of  some  of  its  contained  antimony 
as  oxychloride  :  this  must  be  separated  by  filtration.  The 
solution  is  then  to  be  saturated  with  potassium  carbonate, 
and  a  new  precipitate  will  be  formed.  The  solution  is  to 
be  filtered,  and  made  slightly  acid ;  then  barium  nitrate 
must  be  added  to  it  to  separate  its  sulphur  as  barium 
sulphate,  which  is  to  be  washed,  dried,  and  weighed  :  its 
weight  indicates  the  amount  of  sulphur:  116  parts  are 
equal  to  16  parts  of  sulphur. 

The  precipitate  by  water  of  oxychloride  which  remains 
on  the  filter  is  redissolved  by  hydrochloric  acid,  and  its 
antimony  separated  in  the  metallic  state  by  means  of  zinc. 
The  precipitate  formed  by  potassium  carbonate  may  con- 
tain lead,  copper,  iron,  and  antimony.  It  must  be  treated 
with  nitric  acid  ;  this  dissolves  everything  but  the  antimony, 
which  may  then  be  estimated  as  antimonic  acid. 

It  is  always  best,  before  conducting  the  analysis  of 
antimony  sulphide,  to  affuse  it  with  very  dilute  hydro- 
chloric acid,  in  order  to  dissolve  a  portion  of  the  calcium 
carbonate,  which  may  form  part  of  the  gangue.  As 
the  composition  of  the  antimony  sulphide  is  constant, 
the  following  process  is  sufficient  in  the  assay  of  an 
antimonial  ore  : — 

Boil  the  ore,  after  treatment  with  dilute  hydrochloric 
acid,  with  concentrated  hydrochloric  acid,  which  dissolves 


504  THE   ASSAY   OF   ANTIMONY. 

only  antimony  sulphide,  and  precipitate  the  metal  as  oxy- 
chloride  by  means  of  water. 

Or,  after  all  gangue  soluble  in  dilute  hydrochloric  acid 
has  been  removed,  the  residue  may  be  weighed,  and  then 
acted  on  by  boiling  hydrochloric  acid,  until  all  action  ceases. 
The  residue  must  be  well  washed  with  weak  hydrochloric 
acid,  dried,  ignited,  and  weighed ;  the  loss  of  weight 
corresponds  to  the  percentage  of  pure  antimony  sulphide, 
which  contains  72*7  per  cent,  of  metal. 

Franz  Becker  ('  Zeitschrift  fur  Analyt.  Chemie,'  1878, 
p.  185)  mixes  1  part  of  the  ore  with  3  parts  sodium  car- 
bonate, and  3  parts  sulphur ;  melts  in  a  porcelain  crucible, 
extracts  with  hot  water,  decomposes  the  filtrate  with 
hydrochloric  acid,  and  converts  the  antimony  sulphide 
into  oxide  in  the  usual  manner. 

The  following  method  of  determining  antimony  is  given 
by  Mr.  Sutton  : — 

The  oxide  of  the  metal,  or  any  of  its  compounds,  is 
brought  into  solution  as  tartrate  by  tartaric  acid  and  water ; 
the  excess  of  acid  neutralised  by  neutral  sodium  carbonate, 
then  a  cold  saturated  solution  of  sodium  bicarbonate  added 
in  the  proportion  of  20  c.c.  to  about  O'l  grm.  of  Sb20;3 ;  to 
the  clear  solution  starch  liquor  and  T^  iodine  are  added 
until  the  blue  colour  appears  ;  the  colour  disappears 
after  a  little  time,  therefore  the  first  appearance  of  a  per- 
manent blue  is  accepted  as  the  true  measure  of  iodine 
required. 

1  c.c. -^10^6  =  0-0061  grm.  Sb. 

Detection  of  Antimony  in  Sublimates. — In  the  examina- 
tion of  mineral  bodies  for  antimony,  the  test  substance  is 
often  roasted  in  an  open  tube  for  the  production  of  a 
white  sublimate.  Dr.  E.  Chapman,  Professor  of  Miner- 
alogy at  Toronto,  recommends  for  the  detection  of  anti- 
mony in  this  substance  the  following  process — a  method 
more  especially  available  when  the  operator  has  only  a 
portable  blowpipe-case  at  his  command  : — The  portion  of 
the  tube  to  which  the  chief  part  of  the  sublimate  is 
attached  is  to  be  cut  off  by  a  triangular  file,  and  dropped 


DETECTION    OF    ANTIMONY    IN    SUBLIMATES.  505 

into  a  test-tube  containing  some  tartaric  acid  dissolved 
in  water.  This  being  warmed,  or  gently  boiled,  a  part 
at  least  of  the  sublimate  will  be  dissolved.  Some 
potassium  bisulphate — either  alone,  or  mixed  with  some 
sodium  carbonate  and  a  little  borax,  the  latter  to  prevent 
absorption — is  then  to  be  fused  on  charcoal  in  a  reducing 
flame  ;  and  the  alkaline  sulphide  thus  produced  is  to  be 
removed  by  the  point  of  the  knife-blade,  and  placed  in  a 
small  porcelain  capsule.  The  hepatic  mass  is  most  easily 
separated  from  the  charcoal  by  removing  it  before  it  has 
time  to  solidify.  Some  of  the  tartaric  acid  solution  is 
then  to  be  dropped  upon  it,  when  the  well-known  orange- 
coloured  precipitate  of  antimony  sulphide  will  at  once 
result. 

In  performing  this  test,  it  is  as  well  to  employ  a 
somewhat  large  fragment  of  the  test  substance,  so  as  to 
obtain  a  thick  deposit  in  the  tube.  It  is  advisable  also  to 
hold  the  tube  in  not  too  inclined  a  position,  in  order  to 
let  but  a  moderate  current  of  air  pass  through  it ;  and 
care  must  be  taken  not  to  expose  the  sublimate  to  the 
action  of  the  flame,  otherwise  it  might  be  converted 
almost  wholly  into  a  compound  of  antimonious  and  anti- 
monic  acids,  the  greater  part  of  which  would  remain 
undissolved  in  the  tartaric  acid.  A  sublimate  of  arsenious 
acid,  treated  in  this  manner,  would  of  course  yield  a 
yellow  precipitate,  easily  distinguishable  by  its  colour, 
however,  from  the  deep  orange  antimonial  sulphide.  The 
crystalline  character,  &c.,  of  this  sublimate  would  also 
effectually  prevent  any  chance  of  misconception. 

To  distinguish  Arseniuretted  Hydrogen  from  Antimo- 
niuretted  Hydrogen. — On  passing  a  mixture  of  these  two 
gases  through  a  tube  containing  solid  pieces  of  caustic 
potash,  these  become  covered  with  a  brilliant  metallic 
coating  of  antimony,  whilst  the  arseniuretted  compound 
escapes  undecomposed.  A  lye  of  potash,  density  1-250, 
only  acts  very  slightly  in  a  similar  case.  The  fragments 
of  potash  which  have  become  metallised  by  the  deposit  of 
antimony  are  altered  in  the  air ;  they  soon  become  white 
in  water,  the  metallic  coating  falling  to  the  bottom  ;  but 


506  THE   ASSAY   OF   ANTIMONY. 

when  they  are  attempted  to  be  collected  on  a  filter  they 
dissolve  before  the  liquid  has  even  passed  through.  In 
the  clear  filtrate,  antimony  is  found  in  solution. 

For  the  Separation  of  Tin  from  Antimony  and  Arsenic, 
Dr.  Clemens  Winckler  ('  Zeitschrift  flir  Analyt.  Chemie,' 
1875,  p.  163)  proceeds  as  follows  : — If  the  object  is  an 
alloy  it  is  dissolved  in  a  mixture  of  4  parts  hydrochloric 
acid,  and  5  parts  water,  with  the  addition  of  a  sufficient 
quantity  of  tartaric  acid.  If  the  mixed  metals  exist  as 
sulphides  they  are  collected  on  a  filter,  washed,  and  dis- 
solved upon  it  in  dilute  potash  lye.  The  filtrate  is  mixed 
with  tartaric  acid,  treated  with  a  current  of  chlorine, 
or  with  bromine  in  slight  excess  neutralised  with  hydro- 
chloric acid.  In  either  case  the  solution  is  introduced  into 
a  beaker,  diluted  to  300  or  400  c.c.,  and  so  much  solution 
of  calcium  chloride  of  a  known  strength  is  added  that  the 
subsequently  precipitated  calcium  carbonate  may  exceed 
the  tin  present  by  about  15  times  in  weight.  The  liquid 
is  then  neutralised  with  potassium  carbonate,  potassium 
cyanide  is  added,  and  afterwards  a  slight  excess,  of  potas- 
sium carbonate,  so  that  the  lime  may  be  totally  precipi- 
tated. The  liquid  is  then  heated  till  it  begins  to  boil ;  it  is 
allowed  to  settle,  the  liquid  poured  upon  a  filter  without 
disturbing  the  sediment,  which  is  then  treated  with  fresh 

o  ' 

water,  boiled  up,  allowed  to  settle,  and  the  clear  liquid 
poured  upon  the  filter.  In  this  manner  the  bulk  of  the 
antimony  is  removed. 

The  precipitate  in  the  beaker  is  removed  in  a  little 
concentrated  hydrochloric  acid,  tartaric  acid  is  added, 
the  liquid  again  neutralised  with  potassium  carbonate. 
and  precipitated  with  potassium  cyanide. 

After  boiling,  the  liquid  is  poured  as  above  through 
the  same  filter,  three  successive  portions  of  water  are 
added,  heating  each  time  to  a  boil,  and  the  precipitate  is 
finally  brought  upon  the  filter  and  completely  washed. 
All  the  arsenic  and  antimony  are  now  found  in  the  filtrate, 
and  all  the  tin,  with  an  excess  of  calcium  carbonate,  in  the 
precipitate. 

For  the  assay  of  alloys  of  lead  and  antimony  such  as 


THE   ASSAY   OF   ANTIMONY.  507 

type-metal/ the  comminuted  alloy  is  digested  in  a  flask 
with  concentrated  nitric  acid  till  the  antimony  is  oxidised. 
It  is  then  slightly  diluted  with  water,  supersaturated  with 
ammonia,  and  mixed  with  an  excess  of  ammonium  bi- 
hydrosulphide,  which  must  be  concentrated  and  yellow.  If 
recently  prepared  a  small  quantity  of  flowers  of  sulphur 
is  added.  The  whole  is  digested  in  the  flask  for  some 
time,  heating  at  last  almost  to  a  boil.  The  flask  is  then 
corked  up  and'  let  stand  till  the  deposit,  which  must  be 
of  a  pure  black,  has  subsided,  while  the  supernatant 
liquid  is  yellow.  If  this  is  not  the  case  more  ammonium 
bi-hydrosulphide  is  needed.  When  cold  the  undissolved 
lead  sulphide  is  separated  by  filtration  from  the  solution 
of  the  antimony  sulphide,  washed  with  cold  water,  dried, 
placed  in  a  tared  porcelain  crucible,  the  filter  burnt 
separately  to  ashes,  which  are  added  to  the  precipitate 
along  with  some  sulphur,  and  the  whole  is  ignited  in  a 
current  of  hydrogen.  After  the  crucible  with  its  contents 
has  been  weighed  the  addition  of  sulphur  and  the  ignition 
are  repeated,  in  order  to  find  if  the  weight  is  constant. 
The  lead  is  calculated  from  the  weight  of  the  lead  sul- 
phide. 

The  solution  of  antimony  sulphide  is  mixed,  drop  by 
drop,  with  hydrochloric  acid,  stirring  all  the  time  till  the 
reaction  becomes  slightly  acid.  The  beaker  is  covered 
with  a  glass  plate  and  allowed  to  stand  till  the  antimony 
sulphide  is  deposited.  It  is  digested  at  a  very  gentle  heat 
till  the  odour  of  sulphuretted  hydrogen  has  ceased  ;  when 
cold  it  is  filtered  upon  a  filter,  dried  at  120°  C.,  and  washed 
with  cold  water  to  which  a  few  drops  of  hydrochloric 
acid  have  been  added.  When  air-dry  it  is  kept  at  the 
heat  of  120  °-130°  C.  in  the  hot  air  oven  till  its  weight  is 
constant.  A  weighed  portion  of  this  substance  is  placed 
in  a  bulb-tube  and  heated  in  a  current  of  dry  carbonic 
acid,  at  first  very  gently,  and  afterwards  at  200°-300°. 
The  black-grey  tin  sulphide  remains,  which  is  allowed  to 
cool  in  a  current  of  carbonic  acid  and  weighed. 


508 


CHAPTER  XIV. 

THE   ASSAY   OF  ZINC, 

ALL  bodies  containing  zinc,  usually  found  in  the  assay 
office,  may  be  divided  into  four  classes  : — 

Class  I. — Zinc  ores,  in  which  the  metal  exists  as  oxide 
not  combined  with  silica  : — 

Earthy  zinc  oxide,  ZnO, 

Manganiferous  zinc  oxide,  ZnO  +  (MnO)  . 

Zinc  aluminate,  Gahnite,  ZnO,6Al2O3. 

Franklinite,  3(FeO,ZnO)  +  (Fe2O3,Mn203). 

Anhydrous  zinc  carbonate,  ZnO,C02. 

Hydrated  zinc  carbonate,  ZnO,3II2O  +  3ZnO,002. 

Class  II. — Zinc  ores,  in  which  the  metal  exists,  as  in 
the  former  class,  ass  oxide,  but  partly  or  wholly  combined 
with  silica : — 

Anhydrous  zinc  silicate. 

Hydrated  zinc  silicate,  electric  calamine,  Zn02,Si03  f  ZnO,H20. 

Class  IH, — Zinc  ores,  in  which  the  metal  is  partly  or 
wholly  combined  with  sulphur. 

Zanc  sulphide  (blende,  Black  Jack},  ZnS. 
Zinc  oxysulphide.     (This  is  rare.) 
Zinc  sulphate,  ZnO,  S03,7H20. 
Zinc  selenide,  ZnSe.     (Very  rare.) 

Class  IV. — Alloys. 


ASSAY   OF   OKES   OF   THE   FIRST   CLASS. 

In -order  to  reduce  the  zinc  oxide  contained  in  sub- 
stances of  this  class,  it  is  sufficient  to  mix  them  with  char- 
coal and  expose  them  to  a  white  heat. 


ASSAY   OF   ORES   OF   THE   FIRST   CLASS.  509 

At  the  moment  of  reduction  the  zinc  is  in  a  vaporised 
state.  Its  vapours,  however,  are  readily  condensable,  so 
that  the  operation  may  be  conducted  in  an  ordinary  retort, 
and  all  the  metal  is  deposited  in  the  neck  without  the 
slightest  loss.  It  seems  from  this  that  nothing  is  so  easy, 
at  first  sight,  as  the  assay  of  zinc  oxide  ;  but  it  is  not  so.  It 
is  very  easy  to  reduce  all  the  oxide,  but  it  is  not  so  easy  to 
collect  all  the  zinc  ;  nor  is  it  easy  to  condense  it  all  in  the 
metallic  state,  and  in  consequence  to  determine  the  precise 
proportion  in  the  ore  submitted  to  assay. 

This  difficulty  consists,  firstly,  in  the  deposit  being  ex- 
tended over  a  large  surface,  and  it  often  adheres  very 
strongly  to  the  sides  of  the  retort,  so  that  it  is  nearly  im- 
possible to  detach  it ;  and  secondly,  as  the  neck  of  the 
retort  is  open,  the  air  having  access  to  it,  brings  to  the 
state  of  oxide  all  the  vapour  nearest  the  end  of  the  neck. 
The  proportion  of  zinc  oxidised  is  larger  in  proportion  to 
the  smallness  of  the  quantity  submitted  to  assay,  and  is 
always  very  considerable  where  no  more  than  200  to  400 
grains  are  operated  upon. 

It  is  not,  therefore,  in  the  extraction  of  the  zinc  from 
its  oxide  that  the  assay  is  rendered  partially  uncertain,  but 
in  its  collection. 

The  distillation  of  zinc  requires  a  very  high  tempera- 
ture, and  cannot  be  performed  in  retorts  of  glass  ;  those  of 
earthenware  must  be  employed.  It  is  not  necessary  to  lute 
these  retorts  when  they  are  of  good  quality ;  and  they  are 
better  thin,  because  they  heat  more  rapidly,  and  are  not  so 
likely  to  crack. 

After  the  mixture  of  oxide  and  charcoal  has  been 
introduced  into  the  retort,  it  is  placed  in  the  fire.  The 
neck  ought  to  have  a  long  tube  of  glass,  with  a  narrow  bore 
adapted  to  it,  so  as  to  collect  all  the  zinc  which  may  escape 
from  the  wide  part  of  the  neck  of  the  retort.  This  dis- 
position is  also  convenient,  as  it  does  not  allow  such  a  free 
access  of  air. 

It  is  heated  gradually  until  it  is  white  inside  ;  the  zinc 
is  reduced  and  volatilised,  and  condensed  in  the  neck  :  the 
greater  the  heat,  the  nearer  the  orifice.  The  metal  can  be 


510  THE    ASSAY    OF   ZINC. 

detached  readily  from  the  neck,  if  it  be  well  blackleaded 
inside.  It  is  necessary,  from  time  to  time,  to  observe  the 
state  of  the  neck,  because  when  very  narrow  it  is  often 
obstructed,  and,  if  not  cleaned  out  with  an  iron  rod,  an 
explosion  might  be  caused. 

When  the  operation  is  finished  the  apparatus  is  allowed 
to  cool,  the  retort  taken  out,  placed  carefully  on  its  side, 
and  broken,  in  order  that  any  particles  of  zinc  which  have 
condensed  in  its  dome  may  be  removed. 

If  the  approximate  proportion  of  metallic  zinc  alone  be 
required,  all  is  collected  and  fused  at  a  very  gentle  heat  in 
a  crucible  with  some  black  flux  ;  but  if  the  true  quantity 
of  zinc  is  to  be  estimated  it  must  be  done  in  a  more  exact 
manner.  The  deposit  must  be  collected  with  all  possible 
care ;  the  neck  must  then  be  broken  to  pieces,  and  every 
piece  having  adhering  to  it  either  zinc  or  oxide  must  be 
placed  on  one  side,  and  digested  in  hot  nitric  acid,  which 
takes  up  those  substances.  If  any  be  in  the  glass  tube,  it 
must  be  carefully  cleansed  by  means  of  acid,  and  the  solu- 
tion added  to  that  produced  by  the  digestion  of  the  broken 
neck,  and  the  deposit  mechanically  collected,  in  nitric  acid. 
The  solution  is  then  evaporated  gradually  to  dryness,  and 
heated  to  redness.  The  nitrate,  by  these  means,  is  decom- 
posed and  transformed  into  oxide,  four-fifths  of  the  weight 
of  which  is  equal  to  the  quantity  of  metallic  zinc  produced 
in  the  assay. 

The  foregoing  is  the  method  of  estimation  by  distil- 
lation ;  the  following  is  the  method  of  estimation  by 
difference.  Two  plans  of  assay  in  this  manner  may  be 
adopted :  firstly,  at  an  ordinary  assay  temperature  ; 
secondly,  at  a  very  high  temperature,  as  that  of  an  iron 
assay.  In  all  cases  it  is  necessary  to  commence  with  the 
expulsion  of  all  volatile  bodies  the  ore  may  contain.  If 
water  or  carbonic  acid  alone  be  present,  simple  calcination 
will  do  ;  but  if  carbonaceous  matter,  roasting  must  be  had 
recourse  to. 

When  the  assay  is  made  at  an  ordinary  assay  tempera- 
ture, the  sample  is  finely  pulverised  and  mixed  with  from 
15  to  20  per  cent,  of  equally  finely  pulverised  charcoal, 


ASSAY   OF   ORES   OF   THE   FIRST   CLASS.  511 

and  pressed  into  a  crucible,  on  which  a  cover  is  placed, 
but  not  luted,  and  rapidly  heated  to  whiteness.  When  no 
more  zinc  vapour  is  disengaged  it  is  cooled,  and  the  mixture 
in  the  pot  collected.  The  residue  ought  to  be  pulverulent ; 
but  as  it  is  mixed  with  some  charcoal,  it  is  roasted,  and 
then  weighed.  It  is  evident  that  the  loss  represents  the 
zinc  oxide  ;  the  charcoal  added,  it  is  true,  leaves  a  small 
quantity  of  ash,  but  it  is  too  small  to  be  worth  accounting 
for. 

In  making  the  assay  in  the  manner  described,  it  is  to  be 
feared  that  a  small  quantity  of  the  oxide  might  remain  un- 
decomposed,  and  that  a  part  of  the  residue  might  adhere  to 
the  crucible,  and  could  not  be  detached  ;  and  lastly,  there 
is  always  a  degree  of  uncertainty  as  to  the  state  of  oxida- 
tion in  which  the  iron  will  exist  after  roasting.  No  incon- 
venience of  this  nature  presents  itself  when  the  assay  is 
made  at  a  very  high  temperature.  This  mode  is  the  most 
exact  of  all,  and  leaves  nothing  to  be  desired. 

The  assays  of  zinc  at  a  high  temperature  are  made 
exactly  as  those  of  iron.  They  are  made  in  a  charcoal 
crucible,  with  the  addition  of  fixed  fluxes,  suitable  to  effect 
the  fusion  of  the  gangues  mixed  with  the  zinc  oxide,  if 
they  be  not  fusible  by  themselves.  The  button  is  weighed ; 
it  is  a  compound  of  slag  and  grains  of  iron,  which  are  col- 
lected and  their  weight  ascertained,  and,  by  the  difference, 
that  of  the  slag.  The  weight  of  oxygen  which  the  iron 
has  lost  during  its  reduction  is  then  added  to  it,  and  by 
deducting  from  the  substance  the  weight  of  the  button 
and  the  oxygen  so  obtained,  we  have  the  proportion  of 
zinc  oxide  reduced  in  the  assay.  On  the  other  hand,  by 
deducting  from  the  weight  of  the  slag  the  weight  of  flux 
added,  the  weight  of  earthy  substances  and  irreducible 
oxides  which  were  mixed  with  the  zinc  oxide  is  ascer- 
tained. 

These  results  can  be  shown  in  a  tabular  form,  in  the 
following  manner : — 

Let  m  be  the  weight  of  the  crude  ore,  n  the  weight  of 
the  calcined  ore,  r  the  weight  of  the  flux  added,  /the  weight 
of  the  cast  iron,  s  the  weight  of  the  slag,  o  the  weight  of 


512  THE   ASSAY   OF   ZINC. 

oxygen  combined  with  the  iron,  calculated  from  the  weight 
of  metal  produced,  z  the  weight  of  the  zinc  oxide,  then  : — 

m  crude  ore  =  calcined  ore          .         .        .         .     n 
r  fixed  fluxes    ....  r 


Gives  metal        .        . 
Givesslag.    ,,-       ^ 

Zinc  oxide  n  +  r  —f—  s  —  o 

Flux  added        ,>/-*-:     . 


Earthy  matter   .         .        s  —  r 

The  following  is  an  actual  experiment  by  Berthier  :  — 

100  crude  ore  =  calcined  ore     ,    •  <.-...-    >  ..-  ,^        .     83*3 

10  kaolin  (china  clay)  acted  on  by  acids   .         ...       '.'    10  0 

7  marble  =  lime        .         .         .         .  •  '-•   >        .         .      4'0 

97^3 

Gave  metal    .         .     45*3  1  T      K  61-3  )  T  *  i 

Gave  slag      .         .     16-3  f  Qxygen        (     19.4  f  Total     .        .     807 

Zinc  oxide         .     16-6 

Fluxes  added       .        ,        «,-'-.        »  .",.-.       •     34'0 
Earthy  matters   .        VV'    •         .        .         •        .      2-0 

The  above  result  was  confirmed  by  wet  analysis,  show- 
ing at  once  the  exactitude  of  the  process. 

Determination  of  Amount  of  Zinc  by  the  Wet  Process  in 
Ores  of  the  First  Class.  —  Dissolve  50  grains  of  the  finely- 
pulverised  ore  in  nitric  acid,  evaporate  to  dry  ness,  allow 
to  cool.  Digest  the  cold  mass  with  a  little  dilute  nitric 
acid,  gently  warming  during  the  digestion,  add  water,  and 
then  filter.  To  the  filtered  solution  add  excess  of  caustic 
ammonia,  gently  warm,  and  filter.  The  excess  of  caustic 
ammonia  dissolves  the  zinc  oxide  which  it  at  first  threw 
down,  as  well  as  any  manganese  oxide  that  may  be  present. 
This  solution  containing  the  zinc,  and  probably  manganese, 
must  be  separated  from  the  precipitate  produced  by  the 
ammonia  by  filtration,  the  insoluble  matter  in  the  filter 
washed  with  water  containing  a  little  ammonia,  and  the 
washings  so  obtained  added  to  the  first  strong  filtrate.  If 
no  manganese  be  present,  ammonium  sulphide  may  now  be 
added  to  the  filtered  liquid  until  it  produces  no  further 
white  precipitate  of  zinc  oxide.  The  liquid  and  precipitate 
must  now  be  allowed  to  stand  in  a  warm  place  for  about 
an  hour,  then  filtered,  and  the  zinc  sulphide  on  the  filter 


ASSAY   OF   ORES   OF   THE    SECOND    CLASS.  513 

washed  with  water  containing  a  little  ammonium  sulphide. 
After  a  few  washings  it  is  to  be  dissolved  in  dilute  hydro- 
chloric acid,  and,  if  necessary,  the  solution  filtered.  To 
the  filtered  solution  is  added  excess  of  sodium  carbonate  ; 
zinc  carbonate  is  thrown  down,  which  in  its  turn  is  col- 
lected on  a  filter,  washed,  dried,  separated  from  the  filter, 
ignited,  and  weighed.  Four-fifths  of  its  weight  is  metallic 
zinc.  If,  by  previous  experiments  by  blowpipe  or  other- 
wise, manganese  were  found  to  be  present,  the  ammoniacal 
solution  containing  the  mixed  oxides  must  be  thus  treated : 
Excess  of  acetic  acid  is  to  be  added  to  it,  and  a  stream 
of  sulphuretted  hydrogen  gas  passed  through  it  until  no 
further  precipitation  takes  place  ;  by  this  means  the  whole 
of  the  zinc  is  deposited  as  sulphide,  whilst  the  manganese 
remains  untouched  in  the  liquid.  The  zinc  sulphide  is  to 
be  collected  on  a  filter  and  treated  with  hydrochloric  acid, 
&c.,  as  just  described. 


ASSAY   OF   ORES   OF   THE   SECOXD    CLASS. 

Zinc  silicates  are  not  reducible  by  charcoal  alone  ;  but 
when  in  contact  with  substances  which  have  the  property 
of  combining  with  silica,  they  are  reduced  completely, 
even  at  a  moderate  temperature.  All  the  modes  of  assay 
just  described  for  ores  of  the  first  class  apply  to  those  of 
the  second,  with  the  exception  that  the  flux,  instead  of 
being  merely  reducing,  must  have  a  true  fluxing  property 
also  :  lime  or  magnesia  are  good  fluxes. 


Wet  Determination  of  Zinc  in  Ores  of  the  Second  Class. 

Ores  of  this  class  are  best  decomposed  by  strong  hydro- 
chloric acid  with  a  small  admixture  of  nitric  acid.  When 
thoroughly  decomposed,  and  the  solution  evaporated  to 
dryness,  it  is  moistened  with  hydrochloric  acid,  and  treated 
exactly  as  described  for  Ores  of  the  First  Class. 


L   L 


614  THE  ASSAY   OF   ZIXC. 


ASSAY   OF   ORES   OF   THE   THIRD    CLASS. 

In  order  to  assay  the  substances  containing  sulphur 
which  belong  to  this  class  they  must  be  roasted,  and  then 
treated  as  the  ores  of  the  first  and  second  class.  Zinc  sul- 
phide may  be.  roasted  without  difficulty ;  and  when  the 
operation  is  made  with  care,  the  roasted  ore  contains 
neither  sulphur  nor  sulphuric  acid.  The  only  precaution 
necessary  to  observe  is,  that  the  heat  must  be  carefully 
regulated  at  first,  in  order  to  avoid  fusion  which  might 
take  place,  especially  when  a  certain  amount  of  iron  sul- 
phide is  present.  Towards  the  end  the  heat  may  be  in- 
creased to  decompose  any  sulphate  that  may  be  formed. 
Both  a  reducing  and  fusing  substance  must  be  added  in 
this  case,  as  in  the  last,  in  order  to  determine  the  fusion 
of  the  gangue. 

Wet  Determination  of  Zinc  in  Ores  of  the  Third  Class. 
These  ores  are  to  be  finely  pulverised,  treated  with  strong 
nitric  acid,  at  first  with  a  gentle  heat ;  and  lastly,  boiled 
until  the  sulphur  separates  in  bright  yellow  transparent 
globules,  as  described  under  the  Wet  Assay  of  Copper 
Ores  of  the  Second  Class.  The  solution  so  obtained 
is  to  be  evaporated  to  dryness,  moistened  with  hydro- 
chloric acid,  and  treated  as  described  for  ores  of  the  first 
class. 

If  ores  of  this  class,  or  of  either  of  the  two  former,  con- 
tain copper,  they  must  be  thus  treated  : — 

The  ore  is  to  be  decomposed  by  an  appropriate  acid, 
evaporated  to  dryness,  moistened  with  hydrochloric  acid, 
water  added,  and  the  solution  filtered.  A  current  of  sul- 
phuretted hydrogen  gas  is  now  to  be  passed  through  the 
solution  until,  even  after  violent  agitation,  it  smells  strongly 
of  it.  It  is  now  to  be  filtered,  and  the  black  precipitate 
on  the  filter  contains  all  the  copper  as  copper  sulphide, 
that  substance  being  insoluble  in  dilute  acid,  whilst  in  a 
solution  acidulated  with  either  of  the  strong  mineral  acids 
— as  nitric,  hydrochloric,  or  sulphuric — zinc  is  not  at  all 
acted  on  by  sulphuretted  hydrogen.  The  solution,  now 


VOLUMETRIC  DETERMINATION  OF  ZINC.  515 

freed  from  copper,  is  placed  in  an  evaporating  basin  and 
boiled  for  about  a  quarter  of  an  hour ;  nitric  acid  is  then 
added  to  peroxidise  all  the  iron  present,  and  the  solution 
allowed  to  cool.  When  cold,  the  zinc  is  separated  by 
means  of  ammonia,  and  the  ammoniacal  solution  treated 
as  already  described. 


FOURTH   CLASS.      ALLOYS. 

The  alloys  of  zinc  with  iron,  copper,  and  tin  may  be 
assayed  by  heating  them  to  whiteness  for  about  an  hour 
in  a  charcoal  crucible  with  an  earthy  flux  (calcium  silicate 
is  the  best),  and  weighing  the  resulting  button :  the  loss 
will  be  nearly  equivalent  to  the  quantity  of  zinc  present. 

The  Wet  Determination  of  Zinc  in  Substances  of  the 
Fourth  Class. — These  substances  are  treated  precisely  as 
described  under  the  heads  Wet  Determination  of  Zinc  in 
First,  Second,  and  Third  Classes. 


VOLUMETRIC  DETERMINATION   OF   ZINC. 

Galettfs  Process. — A  good  method  for  volumetrically 
determining  the  amount  of  zinc  in  ores  is  given  in  the 
1  Zeitschrift  fur  analytische  Chemie,'  for  1869,  by  Maurizio 
Galetti,  Chief  Assayer  at  the  Royal  Assay  Office,  Genoa. 
The  following  is  a  description  of  the  process : — Suppos- 
ing zinc  sulphide  (blende)  is  to  be  assayed,  about  half  a 
gramme  of  the  finely  pulverised  ore  is  to  be  treated  with 
concentrated  nitric  acid,  and  boiled  to  incipient  dry  ness, 
until  the  sulphur  left  undissolved  does  not  contain  any 
particles  of  undissolved  ore.  Then  add  strong  hydrochloric 
acid,  and  boil  again  until  no  nitric  acid  is  left.  Calami ne 
(zinc  carbonate)  should  at  once  be  acted  upon  with  hydro- 
chloric acid ;  but,  in  order  to  make  sure  of  the  complete 
oxidation  of  all  the  iron  the  ore  may  happen  to  contain,  it 
is  best  to  add  to  the  acid  a  few  decigrammes  of  pure  po- 
tassium chlorate.  After  having  boiled  this  solution  for  a 
few  minutes,  it  is  diluted  with  distilled  water  ;  a  large 
excess  of  ammonia  is  added  to  the  solution,  which  is  then 

L    L   2 


516  THE    ASSAY   OF   ZINC. 

boiled  and  slightly  acidified  with  acetic  acid.  After  brisk 
agitation,  boil  again  for  a  few  minutes,  and  then  super- 
saturate with  ammonia.  The  liquid  is  then  poured  out  of 
the  flask  into  a  suitable  glass  vessel,  and  the  flask  is  rirsed 
out  with  a  sufficient  quantity  of  distilled  water  to  bring 
the  bulk  of  the  fluid  up  to  half  a  litre.  This  having  been 
done  the  fluid  is  very  cautiously  and  gradually  acidified 
with  dilute  acetic  acid,  one  part  acid  sp.  gr.  1'07  to  10  of 
distilled  water.  Any  large  excess  of  this  should  be  avoided, 
as  the  solution  should  only  be  very  slightly  acid.  As  soon 
as  the  basic  iron  acetate  has  subsided,  the  precipitation  of 
the  zinc  by  means  of  a  standard  solution  of  potassium 
ferrocyanide  may  be  proceeded  with. 

The  ferrocyanide  solution  is  made  by  dissolving  41-25 
grms.  of  'the  said  salt  in  as  much  distilled  water  as  will 
make  the  solution  weigh  exactly  one  kilogramme. 

The  presence  of  compounds  of  lead  (as,  for  instance, 
lead  carbonate,  sulphate,  or  sulphide)  occurring  along  with 
the  ores  of  zinc,  does  not  interfere  with  the  completeness 
of  the  precipitation  of  zinc  as  zinc  ferrocyanide.  This  even 
holds  good  up  to  10  per  cent,  of  metallic  lead.  Since  some 
ores  of  zinc,  especially  calamine,  often  contain  manganese, 
it  is  best  to  add  to  the  ainmoniacal  solution,  before  any 
acetic  acid  is  added,  a  few  drops  (from  2  to  4)  of  bromine, 
in  order  to  convert  the  manganese  protoxide  into  proto- 
sesquioxide,  leaving  the  solution  standing  for  twenty-four 
hours  after  the  addition  of  the  bromine. 

The  ammoniacal  solution  of  zinc  chloride  being  colour- 
less, there  should  be  added  to  it,  previous  to  cautious 
acidification  by  means  of  dilute  acetic  acid,  a  few  drops 
of  tincture  of  litmus,  in  order  to  more  readily  hit  the 
precise  point  of  sufficient  acidification,  which  is  known  by 
the  blue  colouration  changing  to  a  rose-red. 

The  zinc  ferrocyanide  which  is  mixed  with  iron  oxide 
preserves  its  naturally  white  colour  as  long  as  the  liquid 
contains^  free  zinc,  but  its  colour  changes  to  a  greyish- 
white  as  soon  as  a  very  slight  excess  of  the  ferrocyanide 
standard  solution  is  present ;  the  liquid  also  then  becomes 
turbid,  and  the  precipitate  settles  very  slowly.  By  these 


VOLUMETRIC   DETERMINATION   OF   ZINC.  517 

characteristic  signs  the  end  of  the  operation  may  be  always 
recognised.  In  order  to  make  sure,  the  liquid  should  be 
touched  with  a  glass  rod  which  has  been  just  previously 
moistened  with  a  dilute  solution  of  ammoniacal  copper 
nitrate  ;  this  will  have  the  effect  of  indicating  any  excess  of 
the  ferrocyanide  solution,  by  producing  the  more  or  less 
intense  colour  characteristic  of  copper  ferrocyanide.  The 
zinc  solution  should  be  at  a  temperature  of  from  40°  to  50°, 
whereby  the  rapid  subsidence  of  the  zinc  ferrocyanide  is 
promoted. 

Filtration  is  not  necessary,  as  the  presence  of  the  gela- 
tinous silica  (due  to  the  decomposition  of  zinc  silicates 
occurring  in  the  ores  of  that  metal)  does  not  interfere 
with  the  correctness  of  this  method  of  estimating  zinc 
quantitatively.  . 

Fresenius*  gives  the  following  methods  for  the  volu- 
metric determination  of  zinc : — 


1.  METHOD  OF  ScHAFFNER,f  MODIFIED  BY  C.  KUNZELJ  AS  EMPLOYED 
IN  THE  BELGIAN  ZIXC-WORKS;  DESCRIBED  BY  C.  (JROLL.§ 

a.  Solution  of  the  Ore  and  Preparation  of  the  Ammoniacal 

Solution. 

Powder  and  dry  the  ore. 

Take  0*5  grm.  in  the  case  of  rich  ores,  1  grm.  in  the 
case  of  poor  ores,  transfer  to  a  small  flask,  dissolve  in 
hydrochloric  acid,  with  addition  of  some  nitric  acid  by  the 
aid  of  heat,  expel  the  excess  of  acid  by  evaporation,  add 
some  water,  and  then  excess  of  ammonia.  Filter  into  a 
beaker,  and  wash  the  residue  with  lukewarm  water  and 
ammonia  till  ammonium  sulphide  ceases  to  produce  a 
white  turbidity  in  the  washings.  The  zinc  oxide  remain- 
ing in  the  hydrated  ferric  oxide  is  disregarded.  Its  quan- 
tity, according  to  Groll,  does  not  exceed  0*3 — 0*5  per  cent. 
This  statement  probably  has  reference  only  to  ores  contain- 
ing relatively  little  iron ;  where  much  iron  is  present  the 

*  4th  English  edition,  p.  653,  published  by  Churchill  and  Sons. 
t  '  Journ.  f.  prakt.  Chem.'  73,  410.  J  Ibid.  88,  486. 

§  '  Zeitschrift  f.  anal.  Chem.'  1,  21. 


518  THE   ASSAY   OF   ZINC. 

quantity  of  zinc  left  behind  in  the  precipitate  may  be  not 
inconsiderable.  The  error  thus  arising  may  be  greatly 
diminished  by  dissolving  the  slightly  washed  iron  precipi- 
tate in  hydrochloric  acid,  and  adding  excess  of  ammonia. 
But  the  surer  mode  of  proceeding  is  to  add  to  the  original 
solution — after  evaporating  off  the  greater  part  of  the  free 
acid  as  above,  and  allowing  to  cool — dilute  sodium  car- 
bonate nearly  to  neutralisation,  then  to  precipitate  the 
ferric  oxide  with  boiling  sodium  acetate,  to  filter,  and 
wash.  The  washings,  after  being  concentrated  by  evapo- 
ration, are  added  to  the  nitrate,  and  the  whole  is  then 
mixed  with  ammonia  till  the  first  formed  precipitate  is  re- 
dissolved. 

If  the  ore  contains  manganese — provided  approximate 
results  will  suffice — digest  the  solution  of  the  ore  in  acids, 
after  the  addition  of  excess  of  ammonia  and  water,  at  a 
gentle  heat,  for  a  long  time,  and  then  filter  off,  with  the 
iron  precipitate,  the  hydrated  manganese  protosesquioxide 
which  has  separated  from  the  action  of  the  air.  The  safer 
course — though  undoubtedly  less  simple — is,  after  sepa- 
rating the  iron  with  sodium  acetate,  to  precipitate  the 
manganese  by  passing  chlorine,  or  by  adding  bromine  and 
heating. 

If  lead  is  present,  it  is  separated  by  evaporating  the 
aqua  regia  solution  with  sulphuric  acid,  taking  up  the 
residue  with  water  and  filtering  ;  then  proceed  as  directed.* 

b.  Preparation   and   Standardising  of  the   Sodium   Sulphide 

Solution. 

The  solution  of  sodium  sulphide  is  prepared  either  by 
dissolving  crystallised  sodium  sulphide  in  water  (about 
100  grm.  to  1,000-1,200  water)  or  by  supersaturating  a 
solution  of  soda,  free  from  carbonic  acid,  with  sulphuretted 
hydrogen,  and  subsequently  heating  the  solution  in  a  flask 

*  Concerning-  the  direct  treatment  of  roasted  zinc  ores  with  a  mixture  of 
carbonated  and  caustic  ammonia,  comp.  E.  Schmidt  (Journ.f.  pi-akt.  Chem.  51, 
257).  By  this  treatment  the  zinc  oxide,  which  was  combined  with  carbonic 
acid,  is  dissolved,  whilst  that  combined  with  silicic  acid  is,  for  the  most  part, 
left  undissolved. 


VOLUMBTRIC   DETERMINATION   OF  ZINC.  619 

to  expel  the  excess  of  sulphuretted  hydrogen.     Whichever 
way  it  is  prepared,  the  solution  is  afterwards  diluted,  so 
that  1  c.c.  may  precipitate  about  0*01  grm.  zinc.     Prepare 
a    solution  of  zinc  by  dissolving  10  grin,  chemically  pure 
zinc  in  hydrochloric  acid,  or  44-122  grm.  dry  crystallised 
potassium  and  zinc  sulphate  in  water,  or  68-133  grm.  dry 
crystallised  potassium  and  zinc  sulphate   in   water,  and 
making  the  solution  in  either  case  up  to  1  litre  with  water. 
Each  c.c.  of  this  solution  corresponds  to  O'Ol  grm. 
zinc.     Now  measure  off  30-50  c.c.  of  this  zinc  solution 
into  a  beaker,  add  ammonia  till  the  precipitate  is  redis- 
solved,  and  then  400-500  c.c.  distilled  water.     Run    in 
sodium  sulphide  as  long  as  a  distinct  precipitate  continues 
to  be  formed,. then  stir  briskly,  remove  a  drop  of  the  fluid 
on  the  end  of  a  rod  to  a  porcelain  plate,  spread  it  out  so 
that  it  may  cover  a  somewhat  large  surface,  and  place  in 
the  middle  a  drop  of  pure  dilute  solution  of  nickel  chloride. 
If  the  edge  of  the  drop  of  nickel  solution  remains  blue  or 
green  proceed  with  the  addition  of  sodium  sulphide,  testing 
from  time  to  time,  till  at  last  a  blackish  grey  colouration 
appears  surrounding  the  nickel  solution.     The  reaction  is 
now  completed,  the  whole  of  the  zinc  is  precipitated,  and 
a  slight  excess  of  sodium  sulphide  has  been  added.     The 
precise  depth  of  colour  of  the  nickel  must  be  observed  and 
remembered,  as  it  will  have  to  serve  as  the  stopping  signal 
in  future   experiments.     To  make  sure  that  the  zinc  is 
really  quite  precipitated,  you  may  add  a  few  tenths  of  a 
c.c.  more  of  the  reagent,  and  test  again  ;  of  course  the 
colour  of  the  nickel  drop  must   be   darker.     Note   the 
number  of  c.c.  used,  and  repeat  the  experiment,  running 
in  at  once  the  necessary  quantity  of  the  reagent  less  1  c.c., 
and  then  adding  0*2  c.c.  at  a  time  till  the  end-reaction 
is  reached.     The  last  experiment  is  considered  the  more 
correct  one.     The  sodium  sulphide  solution  must  be  re- 
standardised  before  each  new  series  of  analyses — that  is, 
if  it  is  kept  in  bottles  containing  air  ;  if,  on  the  contrary, 
oxygen  is  excluded  by  passing  the  air  through  an  alkaline 
solution  of  pyrogallic  acid   previous  to  its   entering  the 
bottle,  the  solution  would  without  doubt  keep  unaltered. 


520  THE   ASSAY    OF    ZINC. 


c.  Determination  of  the  Zinc  in  the  Solution  of  the  Ore. 

Proceed  in  the  same  way  with  the  ammoniacal  solution 
prepared  in  a  as  with  the  known  zinc  solution  in  b.  Here 
also  repeat  the  experiment,  the  second  time  running  in  at 
once  the  required  number  of  c.c.,  less  1  of  sodium  sulphide, 
and  then  adding  0'2  c.c.  at  a  time  till  the  end-reaction 
makes  its  appearance.  The  second  result  is  considered 
the  true  one.  There  are  three  different  ways  in  which 
this  repetition  of  the  experiment  may  be  made.  You  may 
either  weigh  out  at  the  first  two  portions  of  the  zinc  ore, 
or  you  may  weigh  out  double  the  quantity  required  for 
one  experiment,  and  make  the  ammoniacal  solution  up  to 
1  litre,  and  employ  J>-  litre  for  each  experiment ;  or,  lastly, 
having  reached  the  end-reaction  in  the  first  experiment, 
you  may  add  1  c.c.  of  the  known  zinc  solution,  which  will 
destroy  the  excess  of  sodium  sulphide,  and  run  in  sodium 
sulphide  in  portions  of  0'2  c.c.  till  the  end -reaction  is 
again  attained.  Of  course,  in  this  last  process  to  obtain 
the  second  result,  you  deduct  from  the  whole  quantity  of 
sodium  sulphide  used  the  amount  of  the  same,  correspond- 
ing to  1  c.c.  of  the  zinc  solution. 

If  the  ore  contains  copper,  which  frequently  occurs  in 
the  case  of  blendes,  determine  by  a  preliminary  experi- 
ment the  number  of  c.c.  of  sodium  sulphide  which  are 
necessary  to  precipitate  the  copper,  and  at  the  completion 
of  the  zinc-analysis  deduct  them.  In  this  case,  let  the  drop 
to  be  tested  with  nickel  solution  pass  through  a  small 
filter  on  its  way  to  the  porcelain  plate,  in  order  to  avoid 
the  injurious  influence  of  the  copper  sulphide  on  the  nickel 
reaction.  If,  however,  the  copper  amounts  to  more  than 
2  per  cent.,  remove  it  from  the  acid  solution  by  sulphur- 
etted hydrogen,  evaporate  the  filtrate  with  nitric  acid, 
dilute,  treat  with  ammonia,  and  determine  the  zinc  as 
above. 

In  careful  hands  the  error  will,  according  to  C.  Kiinzel, 
never  exceed  ^  per  cent. 


VOLUMETRIC   DETERMINATION   OF   ZINC.  521 


d.  Further  Modification  of  the  Process. 

To  ascertain  the  point  when  the  whole  of  the  zinc  is 
precipitated  and  the  sodium  sulphide  begins  to  predomi- 
nate, Schaffner*  employed  flocks  of  hydrated  ferric  oxide, 
which  he  produced  by  the  addition  of  a  few  drops  of  ferric 
chloride  to  the  ammoniacal  zinc  solution,  and  which  settled 
at  the  bottom  ;  while  Barreswilf  used  small  pieces  of  white 
porcelain,  which  were  covered  with  ferric  chloride,  and 
thrown  into  the  ammoniacal  zinc  solution.  Sodium  sul- 
phide is  added  till  the  flocks  or  the  pieces  of  porcelain  turn 
black.  In  neither  case  is  the  end-reaction  so  exact  as  with 
nickel  solution. 

With  the  help  of  lead-paper,  however,  the  point  may 
be  hit  with  great  precision.  Moisten  a  piere  of  white 
filter-paper  with  solution  of  lead  acetate,  place  it  on  a 
layer  of  blotting-paper,  drop  some  ammonium  carbonate 
upon  it,  so  as  to  form  a  thin  coating  of  lead  carbonate,  let 
the  blotting-paper  absorb  the  excess  of  moisture,  and  then 
spread  the  lead-paper  on  a  porcelain  plate.  As  soon  as 
you  imagine  the  zinc  to  be  nearly  all  precipitated,  lay  a 
small  piece  of  filter-paper  on  the  lead-paper,  and  then  'dip 
the  end  of  a  blunt  glass  rod  in  the  fluid,  and  press  it  some- 
what gently  on  the  small  piece  of  filter-paper.  When  the 
sodium  sulphide  begins  to  be  in  excess,  a  brown  spot  forms 
on  the  lead-paper.  Fr.  Mohr J  applies  the  lead  reaction  in 
another  manner.  He  makes  an  alkaline  solution  of  lead 
by  warming  together  lead  acetate,  Eochelle  salt  and  solu- 
tion of  soda  ;  he  first  places  a  drop  of  this  on  filter-paper, 
and  then  close  by  a  drop  of  the  precipitated  zinc  solution, 
so  that  the  circle  formed  by  the  spreading  of  the  solution 
to  be  tested  may  cut  the  circle  of  the  lead  solution.  As 
soon  as  the  sodium  sulphide  begins  to  predominate,  the 
portion  of  the  circumference  of  the  lead  circle  which  lies 
in  the  other  circle  turns  black. 

*  l  Journ.  f.  prakt.  Chem.'  73,  410. 

t  '  Journ.  de  pharm.'  1857,  431 ;  'Polyt.  Centralbl.'  1858,  285. 

%  Mohr's  '  Lehrbuch  der  Titririnethode,'  2  Aufl.  377, 


622  THE    ASSAY   OF   ZINC. 


2.  H.  SCHWARZ'S  METHOD.* 

Prepare  an  ammoniacal  solution  as  in  1,  a. 

Heat  gently,  and  mix  with  a  moderate  excess  of  am- 
monium sulphide.  Allow  the  precipitated  zinc  sulphide 
to  subside,  then  filter,  using  a  tolerably  large  plaited  filter 
of  rapidly  filtering  paper,  moistened  with  boiling  water, 
and  warming  the  fluid  to  acelerate  the  operation,  which 
would  otherwise  require  considerable  time.  Wash  the 
precipitate  with  warm  water  mixed  with  a  little  ammonia, 
until  the  last  drops  no  longer  blacken  a  solution  of  lead 
oxide  in  soda. 

Transfer  the  filter  with  the  precipitate  to  a  beaker,  add 
a  dilute  solution  of  slightly  acidified  ferric  chloride,  cover 
with  a  close-fitting  glass  plate,  and  let  the  mixture  stand 
for  ten  minutes ;  then  heat  gently.  Under  these  circum- 
stances the  zinc  sulphide  decomposes  completely  with  the 
ferric  chloride  to  zinc  chloride,  ferrous  chloride,  and  sul- 
phur :  Fe2Cl6  +  ZnS  =  Zn  C12  +  S  +  2FeCl2. 

Now  add  sulphuric  acid,  and  heat  gently  until  tli£ 
sulphur  has  agglutinated.  Filter,  and  wash  the  filter,  and 
determine  the  iron  in  the  fluid  as  protochloride  by  per- 
manganate,f  2  eq.  iron  correspond  to  1  eq.  zinc.  If  the 
quantity  of  zinc  sulphide  is  not  very  great,  the  filter  may 
be  broken,  and  the  zinc  sulphide  washed  into  a  flask 
which  already  contains  the  solution  of  ferric  chloride. 
The  great  objection  to  this  method  lies  in  the  washing  of 
the  zinc  sulphide,  which,  as  is  well  known,  is  a  long  and 
troublesome  operation.  A  possible  loss  of  sulphuretted 
hydrogen  on  mixing  the  zinc  sulphide  with  ferric  chloride 
may  be  prevented  by  conducting  the  decomposition  in  a 
flask,  connected  with  a  U-tube  containing  ferric  chloride. 

*  See  his  '  Anleitucg  zu  Maassanalyseu,'  Nachtrage,  p.  29  (Brunswick). 
Compare  also  v.  Gellhorn  ('  Chem.  Centralbl.'  1853,  291),  who  has  made  many 
analyses  by  Schwarz's  method. 

t  Without  doubt  the  ferric  chloride  might  be  replaced  by  the  ferric  sulphate, 
by  which  means  the  presence  of  hydrochloric  acid  would  be  avoided. 


CARL   MOHR'S   METHOD.  523 

3.  CARL  MOHR'S  METHOD.* 

This  method  is  based  upon  the  following  considera- 
tions : — 

I.  If  a  solution  of  zinc  acetate,  acidified  with  acetic 
acid,  is  mixed  with  an  excess  of  potassium  ferrocyanide, 
the  whole  of  the  zinc  is  thrown  down  in  the  form  of  a 
reddish-yellow  precipitate  of  zinc  ferrocyanide,  Zn3  (Cy6Fe2). 

II.  If  solution  of  potassium  iodide  is  now  added  in  ex- 
cess, we  have  this  decomposition  : — 2[Zn3  (Cy6Fe2)]  4-  2KI  + 
2(A,HO)  =  3[Zn,  (Cy3Fe)J  +  2(KO,A)  +  H2(Cy3Fe)  +  21. 

III.  1  eq.  liberated  iodine  corresponds,  accordingly,  to 
3  eq.  zinc. 

IV.  If  potassium  iodide  is  made  to  act  upon  zinc  ferro- 
cyanide in  a  neutral  fluid,  the  liberated  iodine  acts  upon 
the  potassium  ferrocyanide  present  in  that  case,  which 
leads  to  the  formation  of  a  little  potassium  ferrocyanide  ; 
the  remaining  free  iodine,  therefore,  will  not  indicate,  with 
accuracy,  the  quantity  of  zinc  present.     But  whereas  the 
reaction  actually  takes  place  in  acid  solution  of  zinc  ace- 
tate, as  above  directed,  it  may  be  assumed  that  potassium 
acetate  and  free  hydroferrocyanic  acid  are  formed  ;  and  as 
iodine  exercises  no  appreciable  action  upon  the  latter  sub- 
stance, the  iodine  liberated  in  the  process  indicates,  with 
tolerable  accuracy,  the  amount  of  zinc  present. 

The  process  is  as  follows  : — 

Treat  the  ore  with  aqua  regia,  as  in  1,  a,  and  drive  off 
the  greater  part  of  the  free  acid  ;  nearly  neutralise  with 
sodium  carbonate,  add  sodium  acetate  in  excess,  boil, 
filter,  and  wash  with  boiling  water  mixed  with  a  little 
sodium  acetate.  The  solution  is  free  from  iron :  it  con- 
tains the  whole  of  the  zinc,  but,  in  presence  of  manganese, 
also  the  whole  of  the  latter  metal.  Hence  the  process  is 
not  applicable  in  the  presence  of  manganese. 

Mix  the  solution  of  zinc,  prepared  as  directed,  with 
potassium  ferrocyanide  in  slight  excess,  i.e.  until  a 
sample  of  the  clear  supernatant  fluid  gives  a  blue  precipi- 
tate with  a  ferrous  salt.  Then  add  a  sufficient  quantity 

*  Dingler's  '  Polyt.  Journ.'  148,  115. 


524  THE    ASSAY   OF    ZINC. 

of  potassium  iodide.  The  fluid  acquires  a  brown  colour, 
in  consequence  of  the  liberation  of  iodine  ;  the  white  pre- 
cipitate of  zinc  ferrocyanide  is  suspended  in  the  brown 
fluid. 

Determine  now  the  free  iodine  by  means  of  sodium 
hyposulphite,  and  calculate  3  eq.  zinc  for  each  eq.  iodine. 
The  results  obtained  by  C,  Mohr  are  very  satisfactory. 
The  method  can  be  employed  only  if  the  acetic  acid  solu- 
tion contains  no  other  heavy  metal  besides  zinc,  and,  more 
particularly,  no  manganese. 

For  determining  the  value  of  zinc  powder,  J.  Drewson 
proposes  the  following  method  : — - 

He  prepares  two  solutions,  the  one  of  pure  fused 
potassium  dichromate— say  40  grms.  per  1,000  c.c. — and 
the  other  of  crystalline  ferrous  sulphate,  about  200  grms. 
in  1,000  c.c.  The  iron  solution  must  be  strongly  acidu- 
lated with  sulphuric  acid  to  prevent  oxidation.  In  order 
to  find  the  respective  value  of  the  two  liquids,  10  c.c.  of 
the  iron  solution  are  measured  into  a  beaker,  a  little  sul- 
phuric acid  is  added,  and  the  other  solution  is  dropped 
in  from  a  burette  until  a  drop  of  the  mixture  is  no  longer 
turned  blue  by  potassium  ferrocyanide.  About  1  grm.  of 
the  zinc  powder  is  then  weighed,  placed  in  a  beaker  with 
100  c.c.  of  the  chromic  solution  ;  10  c,c.  of  dilute  sul- 
phuric acid  are  added,  the  whole  is  well  stirred.  10  c.c. 
more  of  the  sulphuric  acid  are  added,  and  allowed  to  act 
for  about  a  quarter  of  an  hour,  with  diligent  stirring. 
When  everything  is  dissolved  except  a  small  insoluble 
residue,  an  excess  of  sulphuric  acid  is  added,  and  50  c.c. 
of  the  iron  solution,  in  order  to  reduce  the  greater  part  of 
the  excess  of  chromate  ;  more  of  the  iron  solution  is  then 
added  from  a  burette,  till  a  drop  displays  a  distinct  blue 
reaction  with  ferrocyanide,  and  the  mixture  is  then  titrated 
back  with  chromate  till  this  reaction  disappears.  From 
the  total  number  of  c.c.  of  the  iron  solution  consumed, 
the  quantity  is  deducted  which  corresponds  to  the  ferrous 
-solution  employed.  The  chromate  contained  in  the  re- 
mainder, if  multiplied  by  0-66113,  shows  the  metallic  zinc 
contained  in  the  powder. 


SEPARATION   OF   COPPER   FROM   ZINC.  525 

In  order  to  separate  copper  from  zinc  by  a  single 
precipitation  with  sulphuretted  hydrogen,  G.  Larsen 
(' Zeitsehrift  fur  analyt.  Chemie,'  1878,  p.  312)  passes 
sulphuretted  hydrogen  into  the  solution,  filters,  washes 
the  precipitate  first  with  hydrochloric  acid  of  sp.  gr. 
1-05,  through  which  sulphuretted  hydrogen  has  been 
passed,  and  then  with  pure  sulphuretted  hydrogen  water. 
Both  the  precipitation  and  the  washing  are  effected  in 
heat. 

Brass,  pinchbeck,  false  gold-leaf,  bronze  not  containing 
tin,  etc.,  are  dissolved  in  nitric  acid  as  directed  for  alloys 
of  silver  and  copper. 

The  acid  liquid  is  diluted  with  water  and  a  current  of 
sulphuretted  hydrogen  is  introduced,  the  vessel  being  kept 
covered  with  a  glass  plate.  This  is  continued  till  the  pre- 
cipitate has  subsided  and  the  liquid  becomes  clear  and 
colourless.  The  precipitate —copper  sulphide — is  poured 
upon  a  filter,  and  the  filtrate  collected  in  an  evaporation- 
basin.  To  prevent  oxidation  the  filtration  must  be  per- 
formed rapidly,  and  the  air  excluded  as  far  as  possible  by 
keeping  the  funnel  and  the  beaker  covered  with  a  glass 
plate.  The  filter  should  be  kept  constantly  full,  till  it 
has  received  all  the  precipitate. 

All  particles  adhering  to  the  sides  of  the  beaker  and 
to  the  gas  delivery  tube,  are  washed  into  the  filter  by 
means  of  a  feather  and  the  washing-bottle.  The  precipi- 
tate is  then  washed  on  the  filter  moderately  with  cold 
water,  a  few  drops  of  sulphuretted  hydrogen  water  being 
added  each  time.  The  precipitate  is  dried,  transferred  to 
a  tared  porcelain  crucible,  upon  the  lid  of  which  the  filter 
is  reduced  to  ashes,  which  are  added  to  the  precipitate. 
The  whole  is  mixed  with  a  few  centigrms.  of  flowers  of 
sulphur,  and  the  crucible  is  covered  with  a  peculiar  lid,  in 
which  a  bent  porcelain  tube  opens,  through  which  dried 
hydrogen  is  introduced  into  the  crucible,  which  is  then 
placed  over  a  lamp,  and  as  soon  as  the  common  air  is 
expelled  from  the  apparatus  it  is  heated  to  redness.  The 
contents  are  then  let  cool  in  the  current  of  hydrogen. 
Thus  is  obtained  pure  cuprous  sulphide,  Cu2S,  which  is 


526  THE   ASSAY   OF   ZINC. 

weighed,  and  from  its  weight  that  of  the  copper  is  calcu- 
lated. 

The  filtrate  containing  the  zinc  is  concentrated  by 
evaporation  to  expel  excess  of  sulphuretted  hydrogen. 
Crystallised  sodium  carbonate  is  then  gradually  added, 
with  stirring  till  the  effervescence  ceases,  the  precipitation 
is  effected,  and  the  liquid  has  an  alterative  reaction.  In 
order  to  lose  nothing  by  spirting,  the  beaker  is  kept 
covered  with  a  glass  plate,  which  is  afterwards  rinsed  into 
the  beaker  by  means  of  the  washing-bottle.  The  liquid  is 
brought  to  a  boil,  filtered,  and  the  precipitate  well  washed 
with  boiling  water.  It  is  dried  and  strongly  ignited,  when 
it  becomes  converted  into  zinc  oxide.  The  filter  is  burnt 
on  the  lid  of  the  crucible.  The  zinc  oxide  is  weighed,  and 
from  it  the  zinc  is  calculated. 

If  lead  is  also  present,  the  solution  of  the  metals  is 
placed  in  an  evaporating-dish,  and  mixed  with  so  much 
moderately  concentrated  sulphuric  acid  as  to  convert  the 
lead  into  sulphate  and  leave  an  excess,  which  is  afterwards 
chiefly  expelled  by  evaporation.  When  cold,  water  and 
a  little  alcohol  are  added ;  the  precipitate  is  poured  upon 
a  filter,  dried  at  120°,  washed  with  cold  alcoholic  water, 
dried,  and  weighed. 

The  filtrate  is  treated  with  sulphuretted  hydrogen,  as 
for  the  determination  of  copper,  etc.  (Rammelsberg). 


527 


CHAPTEE  XV. 

THE    ASSAY   OF   MERCURY. 

MEECURY  is  found  in  the  native  or  metallic  state,  and  as 
sulphide  or  cinnabar  : — 

Native  mercury,  Hg. 

Mercury  sulphide,  cinnabar,  Hg2S. 

Bituminous  mercury  sulphide. 

There  are  other  minerals  of  mercury  met  with,  but 
hitherto  not  in  sufficient  quantity  to  be  worked  for  the 
metal.  They  are  : — 

Zinciferous  mercury  subsulphide. 

Zinciferous  mercury  sulphide. 

Mercury  selenide. 

Mercury  subchloride. 

Mercury  iodide. 

Silver  amalgam  (see  Silver). 

Assay  of  Mercurial  Ores. — The  determination  of  mer- 
cury is  always  made  by  distillation.  In  case  the  mercury 
is  present  in  the  form  of  native  mercury,  or  mercury 
oxide,  it  is  distilled  without  any  addition.  The  ore  (say 
from  500  to  1,000  grains)  is  placed  in  an  iron  or  earthen- 
ware retort,  which  is  set  over  a  suitable  fire,  and  the  heat 
raised  gradually,  and  kept  up,  until  the  whole  of  the 
mercury  has  passed  over.  The  mercury  which  passes 
over  is  collected  either  in  the  neck  of  the  retort,  or  in  a 
receiver  fitted  for  that  purpose — sueh  as  a  glass  flask  kept 
cool  by  affusion  with  water.  When  but  a  small  quantity 
is  operated  upon  (say  150  to  200  grains),  it  is  most  con- 
venient to  use  a  glass  retort,  or  bent  tube  retort,  heating 
it  gradually  over  a  charcoal  fire,  taking  care  to  keep  the 


528  THE    ASSAY   OF   MERCUKY. 

upper  part  so  hot  that  no  metallic  mercury  may  adhere  to 
it.  It  must  be  heated  nearly  to  the  melting  point  of  the 
glass,  and  until  all  the  mercury  has  come  over. 

When  the  operation  is  finished,  the  neck  is  cut  off, 
weighed,  the  mercury  detached,  and  weighed  again  :  the 
loss  of  weight  is  the  amount  of  mercury.  Or  the  metal 
may  be  detached  by  means  of  a  feather,  and  allowed  to 
fall  into  a  basin  of  water,  which,  if  heated  for  a  few 
seconds,  will  cause  the  mercury  to  collect  into  one  glo- 
bule: the  water  may  be  decanted,  and  the  mercury  dried 
at  the  ordinary  temperature,  and  weighed. 

The  mercury  wholly  condenses  in  the  neck  of  the 
retort,  under  the  form  of  a  metallic  dew.  Some  may  by 
chance  pass  off:  but  in  order  to  prevent  such  an  occur- 
rence, the  beak  of  the  retort  is  plunged  into  water,  or  a 
loose  plug  of  linen,  moistened  with  water,  is  introduced 
into  the  neck,  the  end  of  which  is.  plunged  into  water,  by 
which  means  the  neck  of  the  retort  is  kept  constantly  cool, 
and  the  mercury  is  found  deposited  on  the  linen,  from 
which  it  may  be  detached  by  shaking  in  water. 

When  large  quantities  of  substances  containing  mer- 
cury are  operated  upon,  it  is  necessary  to  heat  very 
strongly  towards  the  end,  in  order  that  the  centre  of  the 
mass  may  receive  a  sufficient  amount  of  heat  to  effect  its 
decomposition.  Naked  glass  retorts  cannot  be  used  ;  and 
either  coated  glass  or  porcelain  retorts  must  be  employed. 
In  the  large  way,  as  in  the  distillation  of  amalgams,  &c., 
cast-iron  retorts  are  used. 

As  before  stated,  all  substances  containing  mercury, 
either  in  its  metallic  state  or  as  oxide,  are  distilled  without 
addition,  but  with  the  others  it  is  necessary  to  employ 
some  reagent  which  will  separate  and  retain  the  sulphur, 
selenium,  &c.  ;  which  reagent  may  be  a  metal,  as  iron, 
copper,  or  tin  ;  or  black  flux,  or  a  mixture  of  quick  lime 
and  charcoal :  iron  filings  are  most  often  used.  For 
cinnabar  about  50  per  cent,  of  iron  filings  is  required,  in 
order  to  prevent  any  of  it  being  sublimed ;  the  true  quan- 
tity required  is  only  about  24  per  cent.,  but  an  excess  is 
necessary,  in  order,  as  before  stated,  to  prevent  loss :  50 


ASSAY   IX  THE   DRY   WAY.  529 

per  cent,  of  iron  filings  may  be  employed  for  the  selenides, 
&c.  When  black  flux  is  used,  from  about  50  to  70  per 
cent,  is  employed.  Caustic  -lime  may  be  employed  in  the 
proportion  of  30  per  cent,  mixed  with  30  per  cent,  of  its 
weight  of  charcoal.  After  the  ore  to  be  assayed  is  care- 
fully mixed  with  any  of  the  above  fluxes,  it  is  always 
advisable  to  cover  it,  when  in  the  retort,  with  a  thin  layer  of 
the  flux  employed,  in  order  to  avoid  all  chance  of  any  loss. 

In  estimating  mercury  by  distillation  it  is  necessary, 
especially  if  the  metal  is  in  the  state  of  chloride  or  sul- 
phide, to  take  certain  precautions,  without  which  a 
portion  of  the  sulphide  or  chloride  would  volatilise 
without  decomposition.  H.  Eose  gives  the  following 
directions  for  carrying  out  the  operation: — Introduce 
into  a  glass  tube  capable  of  resisting  fusion,  closed  at  one 
end,  and  measuring  from  35  to  50  centimetres  in  length, 
a  column  of  sodium  bicarbonate,  then  one  of  quick-lime, 
and  then  a  well-blended  mixture  of  the  mercurial  com- 
pound and  quick-lime,  and,  finally,  a  column  of  quick- 
lime. The  open  end  of  the  tube  is  drawn  out  and  bent 
round  so  as  to  enter  a  small  flask  containing  water.  The 
tube  is  heated  as  if  for  an  organic  analysis,  commencing 
at  the  open  end  and  finishing  with  the  sodium  bicar- 
bonate. The  operation  ended,  cut  the  bent  end  of  the 
tube.  Collect  all  the  mercury  in  the  flask,  dry  with  paper, 
and  afterwards  over  sulphuric  acid,  and  then  weigh  it. 

The  quick-lime  should  not  be  replaced  by  hydrate  of 
lime.  That  would  occasion  all  the  inconvenience  of  an 
analysis  of  a  sulphuretted  combination  of  mercury.  The 
water,  acting  on  the  calcium  sulphide,  would  form  sul- 
phuretted hydrogen,  which,  by  dissolving  in  the  water  of 
the  receiver,  would,  in  time,  transform  a  portion  of  the  re- 
duced mercury  into  sulphide.  It  is  advisable  in  some  cases 
to  replace  the  sodium  bicarbonate  by  magnesium  carbonate. 

Combinations  containing  mercury  iodide  are  not  entirely 
decomposed  when  treated  as  above.  Biniodide  and  proto- 
iodide  are  condensed  in  the  extremity  of  the  tube 
simultaneously  with  the  metallic  mercury. 

To  analyse  these  combinations  recourse  must  be  had 

M  M 


530  THE   ASSAY   OF   MERCURY. 

to  metallic  copper,  the  operation  being  similar  to  that 
with  quick-lime. 

Berthier,  who  experimented  with  an  ore  containing 
arsenic,  realgar,  &c.,  and  cinnabar  from  Huanca-Velica, 
in  Peru,  found,  after  very  many  fruitless  experiments,  the 
following  method  best  adapted  to  its  examination  for 
mercury : — 

The  ore  was  heated  in  a  retort  with  four  to  five  times 
its  weight  of  litharge.  From  the  litharge,  the  arsenic 
sulphide,  &c.,  a  fusible  slaggy  mass  was  formed,  while 
the  cinnabar  was  decomposed  into  sulphurous  acid  and 
metallic  mercury.  The  mercury  volatilised  completely  at  a 
moderate  heat,  and  collected  in  the  fore  part  of  the  neck  of 
the  retort  and  in  the  receiver.  The  single  precaution  which 
must  be  observed  for  the  success  of  the  assay,  consists  in 
only  gradually  and  moderately  heating  the  clay  or  glass 
retort,  in  order  to  prevent  its  being  perforated  by  the  cor- 
roding effect  of  the  litharge  before  the  operation  is  ended. 

If  the  assay  sample  is  extremely  poor  in  mercury,  the 
ordinary  assay  method  becomes  somewhat  inconvenient 
and  uncertain,  on  account  of  the  large  quantity  which 
must  then  be  subjected  to  distillation  in  the  assay.  For 
this  case  Berthier  found  it  more  appropriate  to  digest  the 
assay  sample  with  aqua  regia,  wash  it  thoroughly,  evapo- 
rate the  whole  mass  of  fluid  to  dryness,  and  then  treat  the 
dry  mass,  which  contains  all  the  mercury  as  chloride, 
further  in  the  dry  way  He  found  that  if  mercury 
chloride  (corrosive  sublimate)  is  heated  with  litharge,  it 
volatilises  without  undergoing  any  change.  If,  besides 
the  litharge,  coal-dust  is  also  added,  or  if  instead  of  it 
metallic  lead  is  used  in  great  excess,  the  chloride  is 
reduced  to  subchloride,  which  volatilises,  but  not  the 
smallest  drop  of  mercury  is  thus  produced.  The  best 
reducing  agent  for  the  mercury  chloride  contained  in  the 
dry  mass,  is  black  flux,  of  which  three  parts  by  weight  are 
used.  Since  the  mass  to  be  subjected  to  distillation  has 
been  greatly  diminished  by  the  treatment  of  aqua  regia, 
and  the  subsequent  evaporation,  and  no  high  heat  is  now 
required  for  the  decomposition,  the  distillation  may  be 


ASSAY    IN   THE    DRY   WAY.  531 

performed  in  a  glass  retort.  When  the  gangue  in  the 
poor  ore  is  calcium  carbonate,  all  the  lime  is  dissolved 
out,  before  the  treatment  with  aqua  regia,  by  moderately 
strong  acetic  acid. 

By  this  method  the  smallest  trace  of  mercury  in  an  ore 
or  amalgamation  product  can  be  shown  and  determined 
by  its  weight. 

Eschkas  process  for  assaying  mercury  ores  is  given  as 
follows  in  the  'Chemical  News'  for  July  1872.  The 
method  may  be  used  for  cinnabar,  mercuriferous  fahlerz, 
&c.  The  ore  should  be  weighed  in  a  balance  turning 
with  one  milligramme.  The  quantity  of  ore  for  the  assay 
varies  according  to  its  richness,  as  follows  : — 

Ore  containing  up  to  1  per  cent.         .         .10  grammes 

1  ,,10        „         .         .         .5 

10  „  30        „         .         .         .2 

over     30        „         ...     1 

The  ore  is  introduced  into  a  porcelain  crucible,  the  edge 
of  which  has  been  ground  flat,  and  mixed  with  about 
half  its  weight  of  clean  iron  filings  by  means  of  a  glass 
rod,  and  is  then  evenly  covered  with  a  layer  of  iron  filings 
about  5  to  f  inch  thick.  A  concave  cover,  made  of  fine 
gold,  about  two  inches  in  diameter  and  12  to  15  grammes 
in  weight,  is  now  placed  on  the  crucible  after  having  been 
carefully  weighed  ;  the  concavity  is  filled  with  distilled 
w^ater  and  the  crucible  placed  on  a  triangle  and  heated  for 
ten  minutes  by  a  Bunsen  burner  or  Argand  spirit-lamp, 
during  which  time  the  mercury  is  volatilised  and  deposits 
itself  on  the  gold.  The  gold  cover  is  then  removed,  the 
water  poured  off,  and  the  mirror  of  mercury  on  the  convex 
side  washed  with  alcohol  from  a  wash  bottle.  After  being 
dried  in  the  water-bath,  the  cover  is  allowed  to  cool  tho- 
roughly, and  is  then  weighed  in  a  balance  turning  with  ^ 
milligramme  with  50  grammes  in  the  pan.  The  increase 
of  weight  gives  the  quantity  of  quicksilver  in  the  ore. 
During  the  weighing  the  cover  is  placed  on  an  empty 
porcelain  crucible.  The  quicksilver  is  then  driven  off  by 
heating  the  cover  gently  in  the  flame  of  a  Bunsen  burner 

M  M  2 


532  THE   ASSAY    OF   MERCURY. 

or  a  spirit-lamp,  in  a  place  where  there  is  a  good  draught, 
and  the  empty  crucible  and  cover  are  subjected  to  a 
second  weighing  as  a  check.  In  order  that  the  assay 
should  succeed  the  following  conditions  must  be  fulfilled  : 
— The  cover  must  fit  closely,  so  as  to  avoid  loss  of  quick- 
silver, and  must  be  deep  enough  to  hold  a  sufficient 
quantity  of  water  to  keep  it  cool.  The  iron  filings  must 
be  free  from  grease,  which  would  prevent  the  proper 
formation  .of  the  mirror  ;  the  washing  with  alcohol  must 
not  be  omitted,  as  it  removes  all  the  bituminous  sub- 
stances which  spoil  the  mirror,  and  assists  the  drying  ; 
it  must  be -dried  in  a  water-bath  for  two  or  three  minutes, 
cooled  in  the  desiccator,  and  weighed  when  fully  cool. 
When  assaying  rich  ores  the  alcohol  used  in  washing 
the  cover  must  be  collected,  as  it  may  contain  a  little 
amalgam  ;  it  must  be  poured  into  the  concavity  of  the 
cover,  which  will  take  up  any  little  globules  of  quicksilver. 
The  most  exact  results  are  obtained  in  the  case  of  poor 
ores  containing  less  than  ten  per  cent. 

Assay  for  the  Amount  of  Cinnabar  in  an  Ore. — The  ore 
to  be  assayed  is  distilled,  without  addition,  in  a  glass  retort, 
and  the  sublimed  cinnabar  -collected  and  weighed.  The 
ores  containing  mercury  combined  with  sulphur  are  often 
mixed  with  bituminous  matters  and  calcium  carbonate  : 
then,  when  an  assay  is  to  be  made  for  cinnabar,  it  ,often 
happens  that  a  portion  of  it  is  decomposed,  either  by  the 
carbon  present  or  by  the  aid  of  the  bituminous  matter  and 
lime,  and  a  little  metallic  mercury  is  driven  off  with  the 
cinnabar.  In  this  case,  having  weighed  the  mixture  of 
cinnabar  and  mercury,  the  mixture  is  treated  with  nitric 
acid,  which  dissolves  only  the  latter,  and  pure  cinnabar 
remains,  whose  weight  is  taken,  and  the  quantity  of  mer- 
cury dissolved  ascertained  by  the  difference  ;  and  from  that 
the  quantity  of  cinnabar  calculated  which  that  quantity  of 
mercury  would  yield.  Every  86  parts  of  mercury  furnish 
about  100  of  cinnabar. 

If  the  gangue  of  the  ore  be  fixed,  in  the  fire,  the  assay 
may  be  made  by  mere  calcination,  and  the  loss  of  weight 
will  correspond  either  to  the  metallic  mercury,  oxide,  or 
sulphide  it  may  contain. 


ASSAY   IN   THE   WET   WAY.  533 

For  the  determination,  of  mercury  in  the  wet  way  in 
its  usual  ores,  which  are  mixtures  of  cinnabar  with  lime- 
stone, clay,  iron  oxide,  and  bituminous  matters,  the  sample 
is  first  treated  with  hydrochloric  acid,  which  dissolves  the 
lime,  etc.  The  liquid  is  then  poured  off  and  the  residue 
digested  with  aqua  regia,  when  the  mercury  is  dissolved 
as  chloride.  The  solution  is  filtered  off  from  the  insoluble 
residue,  the  greater  part  of  the  free  acid  removed  by 
evaporation,  diluted  and  heated  with  a  solution  of  sul- 
phurous acid,  to  reduce  the  ferric  oxide  to  the  ferrous  con- 
dition. Without  previous  filtration  it  is  then  treated  with 
sulphuretted  hydrogen,  the  precipitate  of  mercury  sulphide 
is  brought  upon  a  weighed  filter,  and  dried  at  100-110°  C. 
Any  free  sulphur  present  may  be  removed  by  digestion 
with  a  solution  of  sodium  hyposulphite.  The  mercury 
sulphide  may  be  afterwards  tested  for  the  presence  of 
other  metals  of  volatilisation. 

If  it  is  intended  to  weigh  mercury  as  mercurous 
chloride  (calomel)  after  reduction  with  stannous  chk>ride, 
the  ore  should  be  dissolved  not  in  aqua  regia,  but  in  a 
mixture  of  hydrochloric  acid  and  potassium  chlorate. 
Free  chlorine  is  expelled  by  heat,  and  the  liquid  is  placed 
in  a  flask  and  mixed  with  a  clear  solution  of  stannous 
chloride,  to  which  hydrochloric  acid  has  been  added,  and 
the  whole  is  boiled  for  a  few  moments.  When  cold,  the 
liquid  is  decanted  off,  the  mercury  rinsed  in  a  crucible, 
washed  with  acid  water,  and  dried  in  the  exsiccator. 

In  amalgams  mercury  is  generally  determined  by 
placing  the  sample  in  a  porcelain  crucible  and  heating  in 
a  current  of  hydrogen  gas,  when  the  mercury  is  volatilised. 
Rammelsbera . 

(This  method,  however,  is  not  applicable  to  the  amal- 
gams of  the  alkaline  metals.) 

VOLUMETRIC   ESTIMATION   OF   MERCURY. 

The  process  we  have  found  most  trustworthy  is  that  of 
M.  J.  Personne,  described  in  the  '  Comptes  Rendus,'  Ivi.  63, 
as  follows.  The  author  says  : — 


534  THE   ASSAY   OF   MERCURY. 

'  The  process  at  which  I  have  arrived,  after  many 
fruitless  attempts,  is  founded  on  a  well-known  fact  —  that 
a  combination  of  mercury  iodide  with  potassium  iodide 
forming  the  double  iodide,  HgI,KI,  gives  a  colourless 
solution.  Thus,  two  solutions  in  equal  quantities,  one 
containing  one  equivalent  of  mercury  bichloride,  the  other 
two  equivalents  of  potassium,  iodide,  being  mixed,  by 
pouring  the  mercurial  solution  into,  that  of  the  potassium 
iodide,  mercury  iodide  will  be  produced  by  the  contact  of 
the  two  solutions,  which  dissolves  in  proportion  to  its 
formation,  until  the  mercurial  solution  added  is  equal  in 
volume  to  that  of  the  alkaline  iodide  used,  according  to 
the  following  equation:  — 


The  slightest  excess  of  bichloride  causes  the  formation  of 
a  persistent  red  precipitate,  giving  the  liquid  a  very  per- 
ceptible red  tint  even  by  artificial  light.  This  colouration, 
which  indicates  that  the  saturation  is  complete,  gives  to 
this  mode  of  estimation  a  precision  and  nicety  quite  as 
great  as  that  of  litmus,  used  to  ascertain  the  saturation  of 
an  acid  by  a  base.  The  mercurial  solution  must  always 
be  poured  into  the  alkaline  iodide  —  not  the  alkaline  iodide 
into  the  mercurial  solution  ;  otherwise,  though  the  last 
reaction  may  be  the  same,  it  is  impossible  to  obtain  exact 
results,  because  the  mercury  iodide  produced,  not  being 
brought  simultaneously  with  its  formation  (in  a  nascent 
state)  into  contact  with  the  alkaline  iodide  with  which  it 
is  to  combine,  becomes  sufficiently  cohesive  to  dissolve 
but  slowly  in  the  potassium  iodide.  Thus,  in  operating 
with  the  same  liquids,  the  quantity  of  alkaline  iodide 
which  must  be  added  to  dissolve  the  mercury  iodide  pre- 
cipitated varies  according  to  the  time  employed  in  effect- 
ing the  estimation,  and  that  in  considerable  proportions 
I  have  no  doubt  that  it  is  through  operating  in  this  way 
that  potassium  iodide  has  hitherto  been  rejected  as  a 
medium  for  the  exact  estimation  of  mercury. 

'Two  normal  liquids  are  necessary  to  effect  this  esti- 
mation. 


VOLUMETRIC   ESTIMATION    OF   MERCURY.  535 

6  1.  Normal  Standard  Solution  of  Potassium  Iodide. — 
Obtained  by  dissolving  33 '20  grammes  of  pure  potassium 
iodide  in  water  enough  to  make  1  litre  of  solution.  10 
cubic  centimetres  of  this  solution  represent  O'l  grin,  of 
metallic  mercury. 

6  2.  Normal  Standard  Solution  of  Mercury  Bichloride. 
Prepared  by  dissolving  13 -55  grammes  of  mercury  bi- 
chloride in  water,  so  as  to  make  1  litre  of  solution.  The 
solution  of  mercurial  salt  is  facilitated  by  the  addition  of 
5  equivalents,  or  30  grammes,  of  sodium  chloride,  which 
has  no  influence  on  the  reaction,  like  all  neutral  alkaline 
salts ;  10  cubic  centimetres  of  this  solution  also  represent 
0-1  grm.  of  mercury.  Of  these  10  centimetres,  divided  into 
100  parts,  each  division  represents  O'OOl  grm.  of  mercury. 
This  mercurial  solution  serves  to  test  the  purity  of  the 
alkaline  iodide  solution  or  to  give  the  standard  of  an 
unknown  solution. 

'  Liquids  ten  times  more  diluted  may  be  prepared 
without  injuring  the  nicety  of  the  reaction  or  the  exact- 
ness of  the  results  ;  fractions  of  a  milligramme  may  thus 
be  estimated. 

'  The  estimation  is  effected  in  the  following  manner : — 
10  cubic  centimetres  of  a  normal  solution  of  iodide  being 
measured  into  a  small  saturating  vessel,  pour  into  it,  con- 
stantly shaking  the  vessel,  the  solution  of  bichloride, 
measured  in  Gay-Lussac's  burette.  If  the  two  liquids  are 
pure,  it  will  require  exactly  100  divisions  of  the  burette 
before  the  light  red  tint  appears  in  the  saturated  liquid  to 
indicate  the  close  of  the  operation.  When  the  mercurial 
solution  is  weak  a  proportionally  larger  quantity  must  be 
added.  If,  on  the  other  hand,  it  is  too  strong,  less  must 
be  added.  As  will  be  perceived,  this  is  very  similar  to 
the  chlorometric  process. 

'  This  new  method  of  estimating  mercury  being  applic- 
able •  only  to  bichloride,  it  became  desirable  to  extend  its 
application  to  a  greater  number  of  mercurial  compounds, 
if  not  to  all.  This  side  of  the  question  presented  diffi- 
culties not  easily  resolved  in  a  satisfactory  manner.  It 
was,  in  fact,  necessary  to  transform  all  the  mercurial 


536  THE   ASSAY   OF   MERCURY. 

compounds  into  a  perfectly  neutral  solution  of  bichloride. 
I  was  obliged  to  set  aside  successively  the  use  of  aqua 
regia,  and  even  of  hypochlorous  acid.  The  great  volatility 
of  mercury  bichloride,  even  in  a  boiling  solution,  caused 
too  great  a  loss.  M.  Eivot's  process — that  is  to  say,  the 
action  of  chlorine  in  a  solution  of  hydrate  of  potash  or 
soda — is  perfectly  successful.  Take,  for  instance,  the 
estimation  of  mercury  in  cinnabar.  Eeduce  one  gramme 
of  cinnabar  to  a  fine  powder.  Weigh  it  on  paper,  and 
introduce  it  into  a  matrass.  Pour  into  the  matrass  20 
cubic  centimetres  of  a  caustic  soda  solution,  with  which 
mix  the  paper  and  its  contents  by  quickly  shaking ;  then 
send  a  current  of  chlorine,  which  need  not  be  washed, 
into  the  liquid.  The  action  of  the  chlorine  produces  a 
slight  heat,  which  is  gradually  brought  to  boiling-point, 
by  which  time  all  the  matter  will  have  disappeared.  To 
ensure  success,  the  temperature  must  be  carefully  managed 
at  the  commencement.  If  it  is  raised  too  quickly,  part  of 
the  matter  remains  undissolved.  The  solution  being  com- 
plete and  saturated  with  chlorine,  it  is  kept  boiling  long 
enough  to  expel  all  the  excess  of  chlorine.  The  boiling 
may  be  prolonged  without  incurring  any  loss  of  bichloride, 
which  is  not  volatile  in  presence  of  alkaline  chloride. 
The  solution  when  cooled  is  poured  into  a  graduated 
tube.  The  matrass  as  well  as  the  tube  for  conducting  the 
chlorine  are  washed  two  or  three  times  with  water,  and 
the  washing  added  to  the  original  liquid,  so  as  to  form  100 
cubic  centimetres  of  solution.  I  effected  the  estimation 
with  the  standard  solution  of  iodide,  of  which  10  centi- 
metres represent  1*0  grm.  of  mercury.  To  saturate  these 
10  centimetres  it  required  115  divisions  of  the  chloromer- 
curial  solution.  These  115  divisions  contain  then  O'lO  grm. 
of  mercury.  Now,  as  all  the  mercury  contained  in  the 
analysed  cinnabar  is  spread  through  the  10,000  divisions 
of  solution,  we  have  the  quantity  of  mercury  found  by  the 
experiment  by  means  of  a  simple  proportion.' 

Mr.  G.  Attwood  gives  the  following  process  for  the 
quantitative  blowpipe  assay  of  mercury.  The  compounds 
to  be  assayed  may  be  divided  into  three  classes.  Class  A, 


BLOWPIPE   ASSAY    OF   MERCURY.  537 

containing  metallic  mercury,  cinnabar,  tiemanite,  sub- 
oxide,  protoxide,  and  mixed  sulphides.  Class  B,  calomel, 
corrosive  sublimate,  and  iodide  of  mercury.  Class  C, 
amalgam  of  gold,  silver,  copper,  lead,  zinc,  tin,  &c. 

Class  A. — 10  to  20  grains  of  the  ore,  finely  powdered 
and  passed  through  a  sieve,  2,000  holes  to  the  square  inch, 
are  mixed  with  5  to  10  times  their  weight  of  powdered 
litharge  and  distilled  over  a  spirit-lamp  in  a  small  glass 
retort,  1^  inch  long  and  ^  inch  in  diameter.  To  this 
retort  is  fitted,  by  means  of  a  cork,  a  glass  tube,  slightly 
curved,  2|-  inches  long  and  -j^ths  of  an  inch  in  diameter. 
The  end  of  this  tube  dips  under  water  contained  in  a 
small  porcelain  crucible.  The  operation  lasts  only  a  few 
minutes.  The  mercury  is  carefully  collected  from  the 
glass  tube  and  crucible.  The  retort  is  broken  up  and  its 
contents  carefully  powdered  and  examined  by  a  lens  for 
mercury.  The  globules  are  then  united  by  gently  warm- 
ing under  water,  and  the  dry  mercury  weighed. 

Class  B. — A  quantity  of  the  finely-powdered  ore,  equal 
to  10  grs.,  is  mixed  with  three  times  its  volume  of  potas- 
sium oxalate,  and  one  volume  of  potassium  cyanide.  The 
apparatus  closely  resembles  that  used  in  Class  A,  but  the 
retort  has  a  small  bulb. 

Class  C. — These  amalgams  are  sometimes  powdered 
with  difficulty,  and  it  is  often  advantageous  to  add  a 
known  weight  of  pure  mercury,  so  as  to  render  them 
semi-fluid  before  distilling.  10  to  30  grs.  of  the  amalgam 
are  usually  taken  for  an  assay.  A  turned  steel  retort  is 
used  for  distillation,  which  is  effected  in  a  small  charcoal 
furnace  heated  by  a  blowpipe  flame  ;  the  head  of  the 
retort  is  accurately  ground  to  fit  over  the  body.  The 
retort,  including  the  cup  and  cap,  is  1  inch  high  ;  the 
neck  of  the  cap  is  2  inches  long.  The  paper  contains 
full-size  illustrations  of  the  different  retorts,  &c.,  which 
are  made  by  Casella.  (See  '  Journal  of  the  Chemical 
Society,'  1879.) 


538 


CHAPTEE  XVI. 

THE     ASSAY    OF    SILVER, 


ALL  argentiferous    substances    may  be  divided  into  two 
classes,  as  follows  : — 

CLASS  I. — Minerals  containing  silver, 

Silver  glance  (AgS)  containing  87  per  cent,  of  Ag. 

Brittle  silver  ore  (6AgS,SbS3)  containing  70'4  per  cent,  of  Ag. 

Light  red  silver  ore  (3AgS,AsS3)  containing  65'4  per  cent,  of  Ag. 

Dark  red  silver  ore  (3AgS,SbS3)  containing  59  per  cent,  of  Ag. 

Light  and  dark  fahlerz  (argentiferous  grey  copper  ore),  containing  from 

5*7  to  18-31-8  per  cent,  of  Ag. 

Argentiferous  copper  sulphide  (Cu2S,AgS)  containing  53  per  cent,  of  Ag. 
Polybasite  9(Cu0S,AgS)  +  (SbS3,AsS3)  containing  72  94  per  cent,  of  Ag. 


Cupel  bottoms. 
Dross. 
Litharge,  etc. 

CLASS  II. — Metallic  silver  and  alloys,  either  native  or 
otherwise. 

General  Observations  on  the  Assay  of  Ores  and  Substances 
of  Class  No.  I. 

In  order  to  separate  silver  from  this  class  of  substances, 
an  alloy  of  the  precious  metal  with  lead  must  be  formed. 
The  different  methods  by  which  this  object  can  be  attained 
are  the  following  :  firstly,  fusion  with  a  reducing  flux  ; 
secondly,  fusion  with  oxidising  reagents  ;  thirdly,  scorifi- 
cation. 

All  substances  containing  lead  in  the  state  of  oxide, 
such  as  carbonates,  phosphates,  &c.,  are  fused  directly 
with  a  reducing  flux,  as  also  are  slags,  old  cupels,  litharge, 
&c.  All  plumbiferous  sulphides,  &c.,  containing  silver, 


.THE    ASSAY    OF   SILVER.  539 

are  assayed  as  for  lead  by  the  processes  already  pointed 
out,  taking  care  to  follow  the  method  which  gives  the 
largest  proportion  of  lead. 

All  argentiferous  minerals  containing  copper  may  be 
assayed  as  copper  ores  ;  because  an  alloy  of  copper  and 
silver  can  be  cupelled  by  means  of  lead. 

In  making  assays  of  silver  with  lead  or  copper,  it  is 
sometimes  necessary  to  commence  the '  operation  by  roast- 
ing the  ore  ;  under  other  circumstances,  also,  argentiferous 
matters  are  roasted. 

There  is  nothing  very  particular  to  be  observed  in 
this  roasting ;  the  temperature  alone  requires  attention  by 
managing  well  at  the  commencement  of  the  operation,  in 
order  to  avoid  softening,  and  especially  to  avoid  a  very 
rapid  disengagement  of  arsenical  vapours,  because  a  very 
considerable  amount  of  silver  may  be  lost  by  that  means. 

All  substances  which  contain  reducible  oxides  are 
fused  with  a  reducing  flux,  as  also  those  from  which  char- 
coal separates  metals  which  alloy  with  lead,  or  metals 
which  do  not  hinder  the  process  of  cupellation  ;  but  it  is 
necessary  to  add  to  the  reducing  flux  a  certain  proportion 
of  litharge,  in  order  to  produce  metallic  lead,  with  which 
the  silver  may  alloy.  A  mixture  of  metallic  lead  and  any 
suitable  flux  may  be  substituted  for  that  of  litharge  and  a 
reducing  flux  ;  but  the  latter  is  preferable,  because  the 
lead  produced  is  uniformly  diffused  throughout  the  whole 
mass  of  flux  &c.,  not  allowing  a  particle  of  silver  to  escape 
its  action. 

The  reducing  agent  employed  in  nearly  all  assays  is 
charcoal,  either  in  its  ordinary  state,  or  as  it  is  found  in 
black  flux.  Starch  and  other  analogous  substances  may 
be,  as  before  mentioned,  substituted  for  it :  crude  argol  is, 
however,  the  best  reducing  agent.  The  portion  employed 
must  be  varied  according  to  circumstances,  so  that  the 
silver-lead  produced  be  not  too  rich,  or  that  too  great  a 
proportion  of  lead  be  reduced.  If  the  silver-lead  be  too 
rich,  much  of  the  precious  metal  may  be  lost  in  the  slag, 
and  if  too  great  a  quantity  of  lead  be  produced,  silver  is 
again  lost,  owing  to  the  long  exposure  to  the  fire  during 


540  THE   ASSAY    OF    SILVER. 

cupellation  ;  and  indeed  this  is  the  most  fruitful  cause  of 
loss,  for  more  is  lost  in  this  manner  than  by  having  too 
little  lead  produced.  In  order  to  know  the  right  propor- 
tions, the  following  data  will  serve  as  a  guide : — 1  part  of 
charcoal  reduces  about  30  parts  of  lead  from  litharge,  and 

1  part  of  black  flux  reduces  about  1  part  of  lead. 

The  fluxes  employed  in  this  kind  of  assay  are  litharge, 
black  flux,  potassium  or  sodium  carbonate,  and  borax. 
Litharge  is  an  exceedingly  convenient  flux,  because  it 
occupies  very  little  room,  and  fuses  without  bubbling,  pro- 
ducing very  liquid  scoriae  with  nearly  every  substance. 
Experiment  has  shown  that  nearly  all  argillaceous,  stony, 
and  ferruginous  substances  fuse  very  well  with  from  8  to  12 
or  more  parts  of  litharge.  If  from  ^  to  1  part  of  black  flux, 
or  ^th  to  -^g-th  of  charcoal,  be  added  to  1  of  ore,  from  ^  a 
part  to  1  part  of  silver-lead  will  be  produced. 

Black  flux  is  employed  in  the  fusion  of  all  substances 
containing  a  large  proportion  of  alumina,  or  in  which  lime 
is  the  predominant  substance — from  2  to  3  parts  of  this 
flux  generally  suffice — 1  part  of  litharge  is  added  to  the 
assay,  which  is  wholly  reduced,  producing  nothing  but 
lead. 

Potassium  or  sodium  carbonates-  produce  exactly 
the  same  effects  as  the  alkali  of  the  black  flux.  A  cer- 
tain quantity  of  charcoal  must,  in  this  case,  be  added  to 
the  assay. 

Schlutter  fuses  the  poor  refuses  of  goldsmiths'  work- 
shops, mixtures  of  fragments  of  crucibles,  glass,  &c.,  with 

2  parts  of  potassium  carbonate,  when  they  are  very  earthy, 
and  with  1  part  only  when  they  contain  much  glass,  adding, 
at  the  same  time,  to  the  mixture,  a  little  litharge   and 
granulated  lead. 

Borax  has,  like  litharge,  the  advantage  of  being  an 
universal  flux  ;  it  is  useful  especially  for  the  fusion  of  sub- 
stances containing  much  lime ;  but  it  is  necessary  to  take 
great  care  in  the  assay,  in  order  to  avoid  the  loss  which  its 
boiling  up  might  occasion.  This  only  applies,  however,  to 
its  use  in  its  ordinary  state ;  if  previously  fused,  that  is, 
used  as  glass  of  borax,  no  particular  care  need  be  taken. 


FUSION   WITH    OXIDISING    REAGENTS.  541 


FUSION   WITH    OXIDISING   REAGENTS. 

Litha  -ge. — The  oxidising  agents  employed  in  the  assay 
of  argentiferous  substances  are  litharge  and  nitre.  Litharge 
attacks  all  the  sulphides,  arsenic-sulphides,  &c.,  and 
oxidises  nearly  all  the  elements,  excepting  silver,  when 
employed  in  sufficient  quantity ;  and  a  quantity  of  lead 
equivalent  to  the  oxidisable  matters  present  is  reduced,  so 
that  there  results  from  the  assay  a  slag  containing  an 
excess  of  lead  oxide,  and  an  alloy  of  lead  and  silver,  very 
little  contaminated  with  foreign  metals,  if  no  copper  be 
present,  and  which  can  be  submitted  directly  to  cupella- 
tion.  This  method  of  assay  is  exceedingly  convenient  and 
quick. 

The  pulverised  mineral  is  well  mixed  with  litharge  and 
the  mixture  placed  in  a  crucible,  which  may  be  very 
nearly  filled,  as  there  is  scarcely  any  boiling  up  when  the 
pot  and  its  contents  are  submitted  to  the  fire.  A  thin 
layer  of  pure  litharge  is  placed  above  the  mixture,  the 
whole  is  then  heated  rapidly,  and  as  soon  as  the  litharge, 
&c.,  is  completely  fused,  the  crucible  is  taken  from  the 
fire.  It  is  inconvenient  to  heat  it  for  any  length  of  time, 
on  account  of  the  corrosive  action  litharge  has  on  the 
substance  of  the  crucible,  which  it  rapidly  destroys. 

The  proportion  of  litharge  which  must  be  employed 
depends  upon  the  nature  and  quantity  of  oxidisable 
matters  present  in  the  ore.  It  ought  in  general  to  be  very 
great,  because  it  is  absolutely  necessary  that  no  sulphurous 
matters  be  present,  so  that  the  slag  may  not  contain  the 
least  trace  of  silver.  But  it  is  known  how  much  litharge 
is  required  to  decompose  the  metallic  sulphides.  Pyrites 
requires  about  50  parts  ;  mispickel,  blende,  antimony  sul- 
phide, copper  pyrites,  grey  cobalt,  and  grey  copper  require 
from  about  twenty-five  to  about  forty  times  their  weight. 
For  sulphide  of  bismuth  10  are  sufficient,  and  for  galena 
or  silver  sulphide  but  4  or  5  parts  need  be  employed.j1 
The  proportion  of  litharge  will  not  be  so  great  for  & 
mineral  containing  much  stony  gangue  as  for  one  entirely 


542  THE    ASSAY    OF    SILVER. 

metallic.  Experiment  has  proved,  that  the  assay  of  rough 
schlichs,  such  as  those  treated  in  the  large  way  by  amalga- 
mation, can  be  made  very  exactly  with  from  10  to  12  parts 
of  litharge. 

Alloys  of  silver  with  the  very  oxidisable  metals,  such 
as  those  of  iron,  antimony,  tin,  zinc,  &c.,  can  be  assayed 
by  means  of  litharge  ;  but  in  order  to  have  a  successful 
result  the  alloys  should  be  reduced  to  a  very  fine  state  of 
division,  so  that  they  must  be  at  least  granulated  ;  and  it  is 
very  often  necessary  to  repeat  the  operation  several  times 
on  the  fresh  alloy  of  lead  produced. 

The  method  of  assay  just  pointed  out  is  inconvenient, 
on  account  of  the  large  quantity  of  lead  it  produces  ;  pyrites 
giving  8.^  parts,  copper  pyrites  and  blende  7  parts,  anti- 
mony sulphide  and  grey  copper  about  6  parts,  &c.  In 
order  to  avoid  this  inconvenience,  part  of  the  oxidation 
I  can  be  performed  by  means  of  nitre.  Nitre  alone,  em- 
ployed in  excess,  oxidises  all  metallic  and  combustible 
substances  found  with  silver,  and  even,  under  certain  cir- 
cumstances, a  portion  of  the  silver  itself;  but  when  the 
proportion  is  insufficient  to  oxidise  the  whole,  and  when 
the  mixture  contains  at  the  same  time  litharge,  after  the 
nitre  has  produced  its  action  the  litharge  acts  in  its  turn 
on  the  remainder  of  the  oxidisable  substances,  and  the 
resulting  lead  carries  down  the  silver  set  free.  So  that,  by 
employing  suitable  proportions  of  nitre  and  litharge,  all  the 
silver  contained  in  oxidisable  minerals  may  be  extracted, 
and  any  quantity  of  lead  required  may  be  thus  alloyed 
with  it. 

As  to  the  requisite  proportion  of  nitre,  it  can  be  come 
at  by  practice,  aided  by  the  following  data.  It  requires 
about  2.^  parts  of  nitre  to  completely  oxidise  iron  pyrites, 
l^for  sulphide  of  antimony,  and  §  for  galena. 

This  determination  can  be  ascertained  at  once  as  fol- 
lows :  fuse  1  part  of  the  mineral  with  30  of  litharge,  and 
weigh  the  resulting  button  of  lead  ;  and  having  fixed  upon 
the  quantity  of  lead  necessary  to  carry  on  the  cupellation 
properly,  deduct  it  from  the  whole  weight  of  the  button, 
and  the  difference  will  be  the  amount  of  lead  necessary  to 


SPECIAL   DIRECTIONS   FOR   THE   CRUCIBLE   ASSAY.  543 

<_ 

leave  the  slag  in  the  state  of  oxide  ;  and  as  it  has  been 
proved  by  experiment  that  1  part  of  lead  requires  *25  to 
•30  of  nitre,  that  is,  from  25  to  30  per  cent.,  it  is  easy  to 
calculate  the  quantity  necessary  to  be  added. 

When  the  ore  contains  sulphur,  the  latter  forms  with 
the  nitre,  potassium  sulphate,  which  swims  on  the  slag  with- 
out combining  with  it. 

The  assay  of  silver  ores  by  means  of  nitre  is  advanta- 
geous and  useful  in  a  variety  of  cases.  If  we  wish  to  deter- 
mine, for  example,  very  exactly  the  percentage  of  silver 
in  a  poor  galena,  a  large  quantity,  say  a  quarter  of  a  pound, 
must  be  fused  with  about  an  ounce  or  an  ounce  and  a  half 
of  nitre,  and  a  quarter  of  a  pound  of  sodium  carbonate, 
or,  better  still,  the  same  quantity  of  litharge,  one  of  either 
of  which  must  be  employed  to  flux  the  gangue  and  tem- 
per the  deflagration.  After  the  fusion,  all  the  contained 
silver  will  be  found  alloyed  with  a  very  small  quantity  of 
lead. 

Sometimes  the  assay  is  made  with  a  larger  quantity  of 
nitre  than  is  requisite  for  the  oxidation,  and  when  the 
mixture  is  perfectly  fused  a  certain  quantity  of  metallic 
lead  is  added,  taking  care  to  cover  the  whole  surface  of 
the  mixture,  either  by  using  granulated  lead  or  a  conve- 
nient mixture  of  litharge  and  charcoal,  or  litharge  and 
galena.  The  shower  of  metallic  lead  passing  through  the 
fluid  mass  alloys  with  all  the  silver  it  finds  in  its  passage, 
and  so  concentrates  it. 

This  process,  however,  cannot  always  be  confidently 
employed.  If  an  excess  of  nitre  be  employed  with  sub- 
stances susceptible  of  forming  peroxides  capable  of  attack- 
ing silver,  such  as  some  cupreous  substances,  the  lead  added 
reduces  the  greater  part,  but  not  the  whole  of  the  silver  in 
the  ore,  so  that  the  assay  will  not  be  perfect. 

Special  Directions  for  the  Crucible  Assay  of  Ores  and 
Substances  of  the  First  Class. 

The  ores  and  substances  belonging  to  this  class  may, 
for  the  convenience  of  assay,  be  further  subdivided  on  the 


544  THE    ASSAY    OF    SILVER. 

following  principle.  It  has  already  been  seen  that  sulphur, 
and  other  substances  having  a  great  affinity  for  oxygen, 
reduce  metallic  lead  from  litharge  in  proportion  to  the 
amount  of  reducing  matter  present ;  and  as  it  is  necessary 
in  this  kind  of  assay  that  no  more  than  a  certain  quantity 
of  lead  alloy  should  be  submitted  to  cupellation,  some  kind 
of  control  must  be  exercised  by  the  assay er,  to  keep  the 
quantity  of  lead  reduced  in  due  and  proper  bounds.  This 
is  readily  accomplished  by  what  is  called  a  '  preliminary 
assay,'  by  which  all  ores  and  substances  of  this  class  are 
divided  into  three  sections : — 1st,  ores  which,  on  fusion 
with  excess  of  litharge,  give  no  metallic  lead,  or  less  than 
their  own  weight  ;  2ndly,  those  which  give  their  own 
weight,  or  nearly  their  own  weight,  of  metallic  lead  ;  Srdly, 
those  which  give  more  than  their  own  weight  of  metallic 
lead.  The  preliminary  or  classification  assay  is  thus  con- 
ducted : — 

Carefully  mix  20  grains  of  the  finely  pulverised  ore 
(all  silver  ores  must  be  passed  through  a  sieve  with  80 
meshes  to  the  linear  inch)  with  500  grains  of  litharge  ; 
place  the  mixture  in  a  crucible  which  it  only  half  fills  ; 
set  the  crucible,  after  careful  warming,  in  a  perfectly  bright 
fire,  and  get  up  the  heat  as  rapidly  as  possible,  so  as  to 
finish  the  operation  in  a  short  time,  to  prevent  the  action 
of  the  reducing  gases  of  the  furnace  on  the  lead  oxide, 
because  if  a  great  length  of  time  were  taken  in  the  opera- 
tion, a  portion  of  the  lead  reduced  might  be  traceable  to 
the  furnace  gases,  and  the  result  of  the  experiment  vitiated. 
After  the  contents  of  the  crucible  are  fully  fused,  and  the 
surface  perfectly  smooth,  the  crucible  may  be  removed 
and  allowed  to  cool,  and  when  cold  broken.  One  of 
three  circumstances  may  now  present  itself  to  the  assayer  : 
1st,  no  lead,  or  less  than  20  grains,  has  been  reduced ; 
2ndly,  20  or  nearly  20  grains,  more  or  less,  may  be 
reduced  ;  and  3rdly,  more  than  20  grains  may  have  been 
reduced. 

Now,  as  it  has  been  already  stated,  200  grains  of  lead 
alloy  is  a  suitable  amount  to  cupel,  and  as  200  grains  is 
the  best  quantity  of  ore  to  submit  to  assay,  it  will  be 


SPECIAL   DIRECTIONS   FOR   THE    CRUCIBLE    ASSAY.  545 

evident  that  ores  and  substances  of  the  second  section,  or 
those  bodies  which  give  their  own  weight,  or  nearly  their 
own  weight,  of  lead  alloy,  simply  require  fusion  with  a  suit- 
able quantity  of  litharge  and  an  appropriate  flux.  Ores  of 
the  first  section  require  the  addition  of  a  reducing  agent,  in 
quantity  equivalent  to  the  standard  amount  of  lead  alloy 
(200  grains) ;  and  ores  of  the  third  section  require  an  equi- 
valent quantity  of  an  oxidising  agent,  or  an  amount  of  some 
body  which  will  oxidise  the  lead  in  excess  of  200  grains  of 
alloy. 

The  reducing  agent  employed  is  argol ;  the  oxidising 
agent  potassium  nitrate.  It  is  necessary,  before  commenc- 
ing an  assay  of  a  silver  ore,  to  determine  how  much  lead  a 
given  weight  of  the  argol  the  assayer  has  in  use  will  reduce  ; 
as  also  how  much  lead  a  given  weight  of  potassium  nitrate 
will  oxidise.  These  assays  are  thus  made  : — 

Assay  of  Reducing  Power  of  Argol. — Carefully  mix  20 
grains  of  the  argol  to  be  tested  with  500  grains  of  litharge 
and  200  grains  of  sodium  carbonate  ;  place  the  mixture  in 
a  suitable  crucible,  and  cover  with  200  grains  of  common 
salt.  (It  is  best  to  mix  two  such  quantities,  and  take  the 
mean  of  the  results.)  Fuse  with  the  precautions  pointed 
out  in  assay  of  substances  of  the  first  class,  containing 
lead. 

Weigh  the  resulting  buttons,  and  take  a  note  of  the 
mean  weight,  which  will  represent  the  amount  of  lead 
reducible  by  20  grains  of  argol. 

Assay  of  Oxidising  Power  of  Potassium  Nitrate. — Mix 
20  grains  of  finely-powdered  potassium  nitrate,  50  grains  of 
argol,  500  grains  of  litharge,  and  200  grains  of  sodium 
carbonate  ;  cover  with  200  grains  of  common  salt,  and  fuse 
as  above.  Weigh  the  resulting  button.  Now  calculate 
the  amount  of  lead  which  should  have  been  reduced  by  50 
grains  of  argol,  and  the  difference  between  that  and  the 
amount  of  lead  reduced  in  this  experiment  will  represent 
the  amount  of  lead  oxidised  by  20  grains  of  potassium 
nitrate. 

Thirty  to  32  grains  of  ordinary  red  argol  reduce  about 
200  grains  of  lead  ;  and  23  grains  of  pure  potassium  nitrate 


54G  THE   ASSAY    OF   SILVER. 

oxidise  about  100  grains  of  lead.  The  assayer  must, 
however,  adopt  the  numbers  found  by  himself  by  experi- 
ment, as  the  samples  of  argol  and  nitre  may  be  more  or 
less  impure.  He  must  also  examine  every  fresh  supply  of 
litharge  for  the  amount  of  silver  it  contains,  in  the  follow- 


ing manner  : — 


Assay  of  Litharge  for  Silver. — Mix  1,000  grains  of 
litharge  with  30  grains  (or  any  other  quantity  that  may, 
by  experiment,  be  found  requisite)  of  argol,  200  grains  of 
sodium  carbonate,  and  cover  with  salt,  as  already  directed. 
Fuse  the  mixture  in  a  suitable  crucible  ;  allow  it  to  cool ; 
break  and  cupel  the  button  obtained,  as  hereafter  to  be 
described  ;  take  a  note  of  the  amount  of  silver  obtained  ; 
and  as  1,000  grains  of  litharge  is  the  standard  quantity  for 
a  silver  assay,  the  amount  of  silver,  indicated  as  above,  is 
to  be  deducted  from  the  amount  of  silver  pbtained  in  the 
assay  of  any  silver  ore,  until  that  quantity  of  litharge  is 
consumed. 

Assay  of  Ores  of  the  First  Section. — Make  a  preliminary 
assay,  as  already  described.  Suppose  10  grains  of  lead 
result ;  then,  as  20  have  furnished  10  grains,  so  200  grains 
of  ore  would  furnish  100  grains  of  lead,  or  100  grains  less 
than  the  quantity  best  adapted  for  cupellation ;  so  that, 
referring  to  the  assay  of  argol,  and  finding  that  from  30  to 
32  grains  reduce  200  grains  of  lead,  then  it  is  clear  that 
the  reducing  power  of  from  15  to  16  grains  of  argol,  in 
addition  to  the  reducing  power  of  200  grains  of  ore,  is 
necessary  to  furnish  200  grains  of  lead  alloy.  In  this  case 
the  ingredients  required  in  the  actual  assay,  or  '  assay 
proper,'  would  stand  thus  : — 

200  grains  of  ore. 
200  grains  of  sodium  carbonate. 
1,000  grains  of  litharge. 
15  to  16  grains  of  argol. 

These  materials  are  to  be  thoroughly  well  mixed, 
placed  in  a  crucible  which  they  about  half  fill,  and  covered 
first  with  200  grains  of  common  salt,  and  then  200  grains 
of  borax,  and  submitted  to  the  fire  with  the  usual  precau- 


ASSAY   OF    ORES   OF   THE   THIRD    SECTION.  647 

tion ;  when  the  flux  flows  smoothly  the  assay  is  complete ; 
it  may  be  removed  and  allowed  to  cool,  the  crucible  broken, 
and  the  button  obtained  must  be*  hammered  into  a  cubical 
form,  and  should  approximate  to  200  grains,  either  more 
or  less,  within  10  grains.  Two  crucibles  must  always 
be  prepared.  It  will  also  be  here  convenient  to  mention 
that  the  argol  and  potassium-  nitrate  are  the  only  sub- 
stances whose  quantities  vary  in  the  assay  of  silver  ores, 
the  amount  of  these  variations  being  determined  by  the 
preliminary  or  classification  assay. 

Assay  of  Ores  of  the  Second  Section. — If  the  preliminary 
assay  of  the  sample  submitted  to  assay  furnish  from  18  to 
22  grains  of  lead,  then  the  assay  proper  may  be  thus 
made : — 

200  grains  of  the  ore, 
200  grains  of  sodium  carbonate,. 
1,000  grains  of  litharge, 

well  mixed  and  covered  with  salt  and  borax  as  above. 
Fuse  with  due  care,  and  reserve  buttons  of  lead  alloy  for 
cupellation. 

Assay  of  Ores  of  the  Third  Section. — If  the  sample  on 
preliminary  assay  furnished  4ft  grains  of  lead,  then  the  200 
grains  employed  in  assay  proper  would  give  400  grains  or 
200  grains  of  lead  in  excess  ;  refer  now  to  note-book  for 
quantity  of  lead  oxidised  by  nitre:  suppose  the  nitre  pure 
as  just  stated,  23  grains  will  oxidise  100,  therefore  46 
grains  are  equivalent  to  200,  and  the  assay  proper  will 
stand  thus  : — 

200  grains  of  the  ore. 

200  grains  of  sodium  carbonate. 
1,000  grains  of  litharge. 

46  grains  of  potassium  nitrate. 

The  potassium  nitrate  is  to  be  weighed  first,  finely  pul- 
verised, and  then  well  mixed  with  the  remaining  sub- 
stances, and  covered  with  salt  and  borax.  The  crucible 
in  this  assay  must  be  larger  than  in  the  two  preceding 
cases ;  the  mixture  should  not  more  than  one-third  fill  it, 

K  M   2 


548  THE   ASSAY   OF   SILVER. 

as  there  is  a  considerable  action  set  up  between  the  oxygen 
of  the  nitre  and  the  sulphur  or  arsenic,  or  any  other  sub- 
stance that  may  be  the  reducing  agent  in  the  ore  ;  for  in 
fact  the  nitre  does  not  directly  oxidise  the  lead,  which 
sulphur  &c.,  might  have  reduced,  but  oxidises  its  equiva- 
lent quantity  of  sulphur,  or  whatever  other  reducing 
substance  there  may  be  in  the  ore,  so  as  only  to  leave  a 
sufficient  amount  to  reduce  200  grains  of  lead,  in  lieu  of 
the  400  as  indicated  by  preliminary  assay,  or  when  the 
reducing  power  of  the  ore  was  allowed  to  come  into  full 
play.  The  buttons  obtained  in  this  case  are  also  to  be 
reserved  for  cupellation. 

Scarification. — Scorification  has,  like  fusion  with  lith- 
arge, the  effect  of  producing  an  alloy  of  lead  capable  of 
cupellation,  and  a  very  fusible  slag  composed  of  lead  oxide, 
and  all  the  matters  foreign  to  silver,  converted  into  the 
state  of  oxide.  In  the  crucible  assay  as  just  described  the 
oxidation  of  these  substances  takes  place  by  the  action  of 
the  litharge,  which  furnishes  at  the  same  time  by  its  re- 
duction the  lead  necessary  to  form  the  alloy,  whilst  in  scori- 
fication  all  the  substances  susceptible  of  oxidation  are 
oxidised  in  the  roasting  by  means  of  the  oxygen  of  the 
air,  and  the  litharge  itself  is  produced  by  the  oxidation  of 
part  of  the  lead  mixed  with  the  ore  to  be  assayed. 

In  this  operation  vessels  termed  scorifiers  (see  p.  136) 
are  employed.  They  are  heated  in  the  muffle  of  the 
cupelling  furnace,  and  as  many  assays  may  be  made  at 
one  time  as  the  muffle  holds  scorifiers. 

Before  introducing  the  scorifiers  into  the  muffle,  a  given 
weight  of  the  ore  reduced  to  powder  is  mixed  intimately 
with  a  certain  quantity  of  granulated  lead,  and  placed  in 
each.  They  must  then  be  heated  gradually  for  about  a 
quarter  of  an  hour,  with  the  door  of  the  muffle  closed,  in 
order  to  fuse  the  lead  ;  then  diminish  the  heat  and  allow 
access  of  air  by  opening  the  door.  The  current  thus  estab- 
lished in  the  muffle  soon  causes  the  commencement  of  the 
roasting  ;  arid  this  roasting  goes  on  without  its  being  neces- 
sary to  continually  agitate  the  mass,  as  in  the  case  of  pul- 
verulent substances. 


SCORIFICATIOX.  549 

During  the  oxidation,^  a  slag  is  formed  on  the  fluid 
metal,  which  is  thrown  towards  the  edges,  and  which,  by 
continually  augmenting,  at  last  entirely  covers  the  bath. 
This  slag,  which  is  often  solid  at  the  commencement,  be- 
comes softer  and  softer,  and  at  last  becomes  perfectly  fluid ; 
because,  in  proportion  to  the  advance  of  the  operation,  the 
proportion  of  lead  oxide  continually  increases.  When  it 
is  judged  that  the  scorification  has  been  carried  far  enough, 
the  melted  matter  is  stirred  with  a  rod  of  iron,  in  order  to 
mix  with  the  mass  the  hard  or  pasty  parts  attached  to  the 
bottom  or  sides  of  the  scorifier.  The  fire  is  then  urged  so 
as  to  completely  liquefy  the  slags.  It  may  be  ascertained 
when  they  are  sufficiently  fluid  by  plunging  into  them  a 
red-hot  iron  rod,  which  must  only  be  covered  with  a  slight 
coating,  capable  of  running  off',  and  not  solidifying  into  a 
drop  at  the  end. 

This  condition  of  liquidity  is  indispensable,  in  order  to 
enable  the  metallic  globules  to  unite  into  a  single  button. 
When  this  end  is  not  attained,  it  is  because  the  scorifica- 
tion has  not  been  carried  sufficiently  far,  or  because  a 
sufficient  quantity  of  lead  has  not  been  added  to  form  the 
flux,  in  which  case  a  fresh  quantity  must  be  added,  or, 
what  is  preferable,  the  assay  recommenced  with  larger 
proportions. 

When  the  operation  is  finished,  the  scorifier  must  be 
removed,  and  its  contents  immediately  poured  into  a 
circular  or  hemispherical  ingot  mould  (see  fig.  29,  p.  67). 
The  metallic  particles  fall  to  the  bottom,  and  as  the  cooling 
proceeds  they  form  a  button  covered  by  the  slag,  which 
is  readily  detachable  by  a  blow  of  a  hammer  ;  it  ought 
to  be  very  homogeneous  and  vitreous,  and  its  colour  vary- 
ing from  brown  to  greenish. 

It  is  always  advisable  to  examine  it,  and  ascertain  if  it 
contain  metallic  globules.  The  button  ought  to  be  as 
ductile  as  ordinary  lead  ;  if  not,  it  cannot  be  cupelled,  and 
must  be  submitted  to  a  fresh  operation.  It  is  in  general 
advantageous  to  push  the  scorification  to  its  greatest  ex- 
tent, because  experiment  has  proved  that  less  silver  is  lost 
than  when  a  large  button  is  cupelled.  Nevertheless,  there 


550  THE    ASSAY    OF   SILVER. 

is  a  limit,  because  if  the  silver-lead  produced  be  too  rich, 
the  least  loss  in  the  shape  of  globules  would  cause  a  not- 
able one  in  the  silver.  Besides,  as  litharge  exercises  a  very 
corrosive  action  on  earthy  matters,  if  the  scorification  be 
continued  for  a  great  length  of  time,  it  sometimes  happens 
the  vessel  is  pierced,  and  the  assay  has  to  be  recommenced. 
The  button  of  lead  remaining  ought  to  weigh  about  200  to 
300  grains,  when  the  ores  treated  are  of  ordinary  richness. 
The  length  of  -time  a  scorification  takes  is  from  half  an 
hour  to  an  hour.  The  scorifier  can  be  rendered  less  per- 
meable to  the  litharge  by  being  rubbed  inside  with  chalk, 
or,  better  still,  red  ochre. 

There  may  be  distinguished  three  distinct  periods  in  the 
operation,  viz.  the  roasting,  the  fusion,  and  the  scorifica- 
tion. At  first  a  strong  fire  is  employed  ;  but  the  doors  of 
the  furnace  are  opened  as  soon  as  the  mixture  is  fused. 
The  mineral,  being  specifically  lighter  than  the  lead,  is  then 
seen  floating  on  its  surface,  or  forming  masses  in  it ;  the 
roastioig  then  commences,  and  from  the  appearance  of  the 
vapours,  the  nature  of  the  combustible  matter  it  contains 
may  be  judged.  Sulphur  produces  clear  grey  vapours  ; 
zinc,  blackish  vapours,  and  a  brilliant  white  flame ;  arsenic, 
whitish-grey  vapours ;  antimony,  fine  red  vapours,  &c. 
When  no  more  fumes  are  seen,  the  mineral  has  disap- 
peared, and  the  fused  lead  is  perfectly  uncovered,  the 
roasting  has  terminated ;  this  generally  requires  from 
eighteen  to  twenty  minutes.  At  this  time  the  fire  is 
urged,  so  as  to  cause  all  the  substances  in  the  scorifier  to 
fuse.  It  can  be  ascertained  that  the  fusion  is  complete  by 
the  following  signs  :  -at  the  instant  the  muffle  is  opened  the 
button  becomes  whitish -red  with  a  greyish-black  band, 
and  there  arise  from  the  melted  mass  clear  white  fumes  of 
lead,  and  the  slag  appears  like  a  ring  encircling  the  metal. 
The  third  period  then  commences  :  the  furnace  is  cooled, 
as  in  the  roasting,  and  the  lead  is  allowed  to  scorify  until 
it  is  entirely  covered  with'  fused  oxide  ;  this  last  period 
generally  lasts  about  fifteen  minutes.  The  fire  is  then 
increased  for  about  five  minutes,  and  the  contents  of  the 
scorifier  poured  into  the  mould. 


SCORIFICATIOX.  551 

The  process  of  scorification  is  applicable  to  all  argent- 
iferous matters,  and  is  at  the  same  time  the  most  exact 
method  of  assay,  as  also  the  most  convenient,  when  a  large 
number  of  assays  are  required  at  the  same  time,  because 
they  are  entirely  executed  in  the  muffle,  which,  with  most 
assayers,  is  generally  hot :  it,  however,  requires  a  greater 
number  of  vessels — as  cupels,  &c. 

When  the  silver  ores  are  stony,  the  lead  oxide  formed 
during  the  roasting  combines  with  the  gangue,  forming  a 
fusible  compound,  whilst  the  remaining  lead  alloys  with 
the  silver.  When  the  ores  are  metallic,  the  oxidisable 
bodies  absorb  oxygen  from  the  atmosphere ;  and  the 
oxides  so  formed  combine  with  the  litharge  produced  at 
the  same  time,  forming  a  compound  which  becomes  very 
fusible  in  proportion  as  the  lead  oxide  increases ;  and  if 
the  scorification  has  not  been  pushed  sufficiently  far,  the 
button  will  contain,  besides  silver  and  lead,  a  little  copper, 
which  will  not,  however,  interfere  with  the  cupellation. 
There  is  this  one  peculiarity  about  scorification,  that  how- 
ever small  the  proportion  of  lead  may  be  that  is  used,  at 
the  end  of  the  operation  the  slag  does  not  contain  any 
oxysulphide.  For  instance,  even  when  oxysulphides  are 
produced  in  the  course  of  scorification,  they  are  completely 
decomposed  in  the  roasting,  and  in  consequence  it  is  very 
rarely  that  the  slag  retains  any  proportion  of  silver ;  and 
as  to  the  proportion  of  lead  employed,  only  just  enough 
to  render  the  slag  liquid,  and  to  produce  sufficient  lead 
for  cupellation,  is  necessary. 

It  is  different,  however,  when  the  sulphides  and  arsenio- 
sulphides  are  assayed  by  means  of  litharge  ;  for  from  30 
to  50  parts  of  that  substance  must  be  employed  to  prevent 
the  scorke  retaining  any  silver,  or,  as  already  pointed  out, 
a  certain  proportion  of  nitre  must  be  added. 

All  scorifications  may  be  conducted  by  the  simple 
addition  of  lead  ;  but  it  has  been  proved  that  the  opera- 
tion proceeds  more  quickly,  and  with  less  danger  to  the 
scorifier,  when  borax  is  employed.  This  salt  dissolves  the 
oxides  in  proportion  as  they  are  produced,  as  also  the 
gangues,  and  forms  a  very  liquid  slag  from  the  commence- 


65^  THE   ASSAY   OF   SILVER. 

ment  of  the  operation,  which  does  not  happen  when  lead 
alone  is  used,  because  litharge,  which  can  alone  cause  the 
fusion,  is  only  present  in  the  slag  in  sufficient  proportion 
at  a  very  advanced  stage  of  the  operation. 

When  the  slag  is  liquid  at  the  beginning  of  the  opera- 
tion (as  occurs  in  the  use  of  borax),  it  is  continually  thrown 
on  the  sides  of  the  scorifier,  and  forms  a  ring  on  the  sur- 
face of  the  bath,  leaving  in  the  centre  the  metallic  sub- 
stance, having  a  considerable  extent  of  surface,  which  is 
continually  diminishing. 

The  current  of  air,  being  thus  directly  in  contact  with 
the  fused  metals,  rapidly  causes  their  oxidation,  which 
does  not  take  place  when  the  semi-fluid  substances  float 
here  and  there  on  the  metallic  bath.  The  proportion  of 
lead  and  borax  necessary  for  a  scorification  varies  exceed- 
ingly, according  to  the  nature  of  the  substance  under 
assay,  and  ought  to  be  greater  in  proportion  as  the  sub- 
stances, or  resulting  oxides,  are  difficult  of  fusion.  In 
ordinary  cases  12  parts  of  lead,  and  1  of  glass  of  borax, 
are  employed ;  but  sometimes  32  of  lead,  and  3  of  borax, 
are  required.  A  large  proportion  of  borax  is  useful, 
especially  when  the  substances  contain  much  lime,  zinc 
oxide,  or  tin  oxide. 

Instead  of  borax,  glass  of  lead  may  be  employed.  It 
acts  as  a  flux  on  silica ;  but  its  action  is  much  less  efFec- 
'tive  than  that  of  borax. 

There  are  some  substances  which  scorify  with  a  small 
proportion  of  lead.  Thus,  for  galena  and  copper  sulphide, 
2  parts  of  lead  suffice ;  but  8  parts  are  required  for  ores 
which  contain  much  gangue. 

Silver  antimonide  can  be  scorified  with  8  parts  of  lead, 
but  according  to  experiments  made  in  the  Hartz,  it  appears 
that  the  slag  retains  about  y^^th  of  silver ;  with  16  parts 
of  lead  ?|[trtll  of  fine  metal  is  still  lost ;  but  with  3  of  borax 
and  16  of  lead  not  the  slightest  trace  remains  in  the  slag. 

It  is  very  difficult  to  separate  tin  and  silver  by  the  dry 
way.  The  best  method  is  to  roast  the  alloy  in  a  scorifier, 
adding  to  it  16  parts  of  lead  and  3  of  borax  at  least,  and 
operating  as  before  described. 


ASSAY   OF   SUBSTANCES   OF   THE   FIRST   CLASS.  553 

Speiss  almost  always  contains  silver,  and  is  one  of  the 
most  difficult  substances  to  assay.  If  nickel  be  present, 
the  button  cannot  be  cupelled.  Generally,  speiss  may  be 
scorified  with  1 6  parts  of  lead  ;  and  the  same  operation  is 
gone  through  twice  or  thrice,  adding  each  time  a  fresh 
quantity  of  lead.  The  operation  wrould  probably  succeed 
by  roasting  the  speiss  in  the  scorifier  before  adding  the  lead. 

Special  Instructions  for  the  Scorification  Assay  of  Ores 
of  the  First  Class. — This  mode  of  assay  has  an  advantage 
over  the  crucible  assay  just  described,  inasmuch  as  if 
properly  conducted  no  preliminary  assay  is  required  :  but 
this  is  greatly  counterbalanced  by  the  fact  that  not  more 
than  50  grains  of  ore  can  be  operated  on  in  one  scorifier, 
and  that  good  or  trustworthy  results  cannot  be  obtained 
by  this  method  unless  four  scorifiers  are  employed  for 
each  assay,  so  that  in  all  200  grains  of  ore  may  be  em- 
ployed. There  are  thus  employed  four  scorifiers  to  three 
crucibles,  and  four  cupels  to  two  cupels ;  as  in  one  case 
four  buttons  are  to  be  submitted  to  cupellation,  and  in 
the  other  only  two.  When  very  rich  copper  ores,  how- 
ever, have  to  be  assayed  for  silver,  the  plan  by  scorifica- 
tion  is  very  useful,  as  in  the  crucible  operation  much 
copper  is  reduced  with  the  lead,  so  as  to  require  a  very 
large  quantity  of  lead  for  its  conveyance  as  oxide  into  the 
cupel.  This  class  of  assay  will,  however,  be  particularly 
noticed  under  the  head  Assay  of  the  Alloys  of  Silver. 

Assay  in  Scorifier. — Weigh  out  300  grains  of  granu- 
lated lead,  place  them  in  a  scorifier,  then  add  50  grains 
of  pulverised  fused  borax,  and  50  grains  of  the  ore  to  be 
assayed,  wrell  mix  them  in  the  scorifier  by  aid  of  a  spatula, 
and  cover  the  mixture  with  other  300  grains  of  granu- 
lated lead  :  prepare  in  this  way  four  scorifiers,  place  them 
in  the  muffle  with  the  tongs  (6,  fig.  28,  page  66)  and  care- 
fully watch  them  with  all  the  precautions  before  pointed 
out :  when  the  surface  of  the  metal  is  quite  covered  with 
fused  oxide,  pour  the  contents  of  each  scorifier  into  one 
of  the  hollows  of  the  mould  depicted  at  fig.  29,  page  67. 
When  the  mass  of  slag  and  metal  is  cold,  separate  the 
latter  from  the  former  by  means  of  the  hammer  and  anvil, 


554  THE   ASSAY    OF   SILVER. 

hammer  the  metal  into  the  form  of  a  cube,  and  reserve  it 
for  cupellation. 

Assay  of  Substances  of  the  First  Class  admixed  with 
Native  or  Metallic  Silver. — The  same  kind  of  calculation 
is  necessary  in  the  assay  of  ores  as  above,  as  in  the  case  of 
copper  ores  containing  metallic  copper.  The  sample  must 
be  carefully  weighed.  Suppose  it  to  weigh  2,500  grains. 
It  must  be  pulverised,  and  as  much  as  possible  passed 
through  the  sieve  with  eighty  meshes  to  the  linear  inch. 
It  will  be  thus  divided  into  two  parts  :  the  one  passing 
through  the  sieve  is  mineralised  silver — that  is,  silver  ore 
of  various  kinds  mixed  with  earthy  matter,  and  a  very 
small  quantity  of  metallic  silver  which  has  been  sufficiently 
divided  to  pass  through  a  sieve  of  such  a  degree  of  fine- 
ness ;  the  other,  impure  metallic  silver,  which  has  been 
unable  to  pass  through  the  sieve.  The  weights  of  both 
portions  are  carefully  taken,  and  thus  noted — 

Rough  metallic  silver       .         .         .         .  5 '07  grs. 

Ore  through  sieve 2494-93    „ 

Total  weight  of  sample    ....     250U-UO    „ 

Assay  the  ore  which  passed  through  the  sieve  as 
already  directed,  and  the  rough  silver  as  directed  under 
the  head  Assay  of  Silver  Alloys.  Note  the  quantity  of 
silver  obtained  in  each  experiment.  Thus :  suppose  200 
grains  of  ore  yielded  2  grains  of  fine  silver,  and  the  5 -07 
grains  of  rough  silver  4  grains  of  fine  silver  by  cupella- 
tion, the  number  of  ounces  of  fine  silver  in  the  ton  is  thus 
calculated. 

On  referring  to  Table  III.  in  Appendix,  it  will  be  found 
that  if  200  grains  of  ore  yield  2  grains  of  fine  silver, 
1  ton  will  yield  326  oz.  13  dwts.  8  grs.  of  fine  silver ; 
so  that  the  average  produce  of  the  ore  is  the  above 
amount. 

Then,  if  5 "07  grains  of  rough  silver  yield  4  grains  of 
fine  silver,  200  grains  would  yield,  by  calculation,  159 '763 
grains  of  fine  silver. 

Thus— 

200  x  4      n  -ft  *„„ 

=159''03 


ASSAY   OF   SUBSTANCES   OF   THE   FIRST   CLASS.  555 

Now,  by  referring  to  Table  HI.  in  the  Appendix,  it 
will  be  found  that  200  grains  of  ore  give  159  grains  of  fine 
silver  =  2-5, 970  ounces  per  ton:  and  that  200  grains  of 
ore  give  '763  grains  of  fine  silver =124  ozs.  12  dwts. 
11  grains  ;  therefore,  the  5*07  grains  of  rough  silver  con- 
tain after  the  rate  of  26,094  ozs.  12  dwts.  11  grs.  per  ton, 
thus — 

25,970  ozs.  + 124  ozs.  12  dwts.  11  grs.  =  26,094  ozs.  12  dwts.  11  grs. 

Thus  we  have — 

•ozs.         dwte.         grs. 

Average  produce  of  ore      .        „         •        « •        326         13  8 

Average  produce  of  rough  silver         .         .     26,094         12         11 

per  ton  of  20  cwts. 

Then,  as  in  the  case  of  the  copper,  multiply  the  weight 
and  produce  of  each  portion  together,  add  the  resulting 
total  products,  and  divide  the  sum  by  the  weight  of  the 
sample.  For  this  purpose  it  is  better  to  reduce  the  penny- 
weights and  grains  to  their  decimal  values.  Thus  13  dwts. 
8  grs.  is  nearly  equal  to  *67  of  an  ounce,  and  12  dwts.  11 
grs.  to  -62  of  an  ounce  ;  therefore  trie  quantities  above  will 
stand  thus— 326-67  ozs.,  and  260,94*62  oza. 

Then        326-67  x  2494-93  =  8150187831 
and      26094-62  x        5-07  =  132296-7234 
and    815018-7831  +  132299-7234  =  373.9  QZ 
2500 

or  378  ozs.  18  dwts.  (nearly)  per  ton  of  the  original  sample, 
before  pulverising  and  sifting. 

In  every  case  of  assay  yet  described,  it  may  beraentioned 
that  if  the  sample  contained  gold,  the  whole  of  that  metal 
will  be  found  with  the  silver,  as  obtained  by  cupellation, 
and  may  be  separated  as  stated  in  the  chapter  on  the  Assay 
of  Gold. 

Cupellation. — Cupellation  is  one  of  the  most  ingenious 
operations  that  can  be  imagined  ;  it  has  been  known  from 
time  immemorial,  has  many  characters  in  common  with 
scorification,  and  is  effected  in  nearly  the  same  manner. 
Like  that,  it  has  for  its  end  the  separation  of  silver  and 
gold  from  different  foreign  substances,  by  means  of  lead ; 
but  it  differs  in  this,  that  the  scorias  produced  are  absorbed 
by  the  substance  of  the  vessel  named  a  cupel,  in  which 


556  THE   ASSAY   OF    SILVER 

the  operation  is  made,  instead  of  remaining  on  the  melted 
metal,  the  latter  remaining  uncovered  and  in  contact  with 
the  air,  so  that  the  extraneous  metals  are  not  only  oxi- 
dised, but  also  all  the  lead  ;  and  there  remains  nothing 
but  the  pure  metals,  silver  and  gold,  or  an  alloy  of  them, 
in  the  cupel. 

Cupellation  requires,  as  an  indispensable  condition, 
that  the  slag  should  have  the  property  of  penetrating  and 
soaking  into  the  body  of  the  substance  forming  the  cupel  ; 
it  is,  therefore,  only  applicable  to  a  certain  number  of 
substances,  and  not  to  all,  like  scorification.  Lead  and 
bismuth  oxides,  in  a  state  of  purity,  are  the  only  oxides 
which  possess  the  property  of  soaking  into  the  cupel  ;  but 
by  the  aid  of  one  or  the  other,  various  oxides  which  by 
themselves  form  infusible  scoriae  on  the  cupel,  acquire  the 
property  of  passing  through  it :  therefore,  on  making  a 
cupellation,  it  is  necessary  to  fuse  the  substance  with  a 
sufficient  proportion  of  lead  or  bismuth,  so  that  the  oxides 
they  produce  may  combine  with  the  oxides  of  all  the  foreign 
metals  produced  in  the  operation,  and  carry  them  into  the 
body  of  the  cupel. 

This  proportion  varies  with  the  nature  of  the  sub- 
stances cupelled,  and  other  circumstances.  The  quantity 
required  in  ordinary  cases  will  be  mentioned  hereafter. 

The  cupels  or  porous  vessels  in  which  the  operation  is 
made,  ought  to  have  a  sufficiently  loose  texture  to  allow 
the  fused  oxides  to  penetrate  them  easily,  and  at  the  same 
time  to  possess  sufficient  solidity  to  enable  them  to  bear 
handling  without  fracture  ;  and,  moreover,  they  ought  to 
be  of  such  a  nature  as  not  to  enter  into-  fusion  with  either 
lead  or  bismuth  oxide.  For  a  description  of  their  mode  of 
manufacture,  see  p.  133. 

The  following  is  the  method  in  which  an  ordinary 
cupellation  is  conducted  : — The  furnace  being  heated,  the 
bottom  of  the  muffle  is  covered  with  cupels,  placing  the 
largest  towards  the  end  ;  and  if  they  are  required  to  be 
heated  as  quickly  as  possible,  they  may  be  placed  upside 
down,  and  turned,  at  the  instant  of  use,  by  means  of  the 
tongs.  When  the  interior  of  the  muffle  is  reddish-white, 


ASSAY   OF   SUBSTANCES   OF   THE    FIRST   CLASS.  557 

the  matters  to  be  cupelled  may  be  introduced.  When  the 
cupels  have  been  placed  in  their  proper  position,  great 
care  must  be  taken  from  the  commencement  to  blow  out 
of  them  all  cinders,  ashes,  and  other  extraneous  substances 
which  may  have  fallen  into  them. 

The  substance  to  be  cupelled  is  sometimes  an  alloy, 
which  can  pass  without  addition  of  lead,  and  sometimes 
a  compound,  to  which  lead  must  be  added.  In  the  first 
case,  the  alloy  is  laid  hold  of  by  a  small  pair  of  forceps, 
and  deposited  gently  in  the  cupel.  In  the  second  case,  the 
substance  to  be  cupelled  is  enveloped  in  a  sheet  of  lead  of 
suitable  weight,  and  placed,  as  before,  in  the  cupel ;  or  the 
necessary  quantity  of  lead  may  be  first  placed  in  the  cupel, 
and  when  the  lead  is  fused,  the  substance  to  be  cupelled 
added,  taking  care  not  to  agitate  the  melted  mass  and 
cause  loss  by  splashing.  If  the  substance  to  be  cupelled 
is  in  very  small  pieces,  as  grains  or  powder,  it  must  be 
enveloped  in  a  small  piece  of  blotting-paper,  or,  still 
better,  in  a  piece  of  very  thin  sheet  lead,  giving  it  a  slightly 
spherical  form,  and  dropping  it  gently  into  the  mass  of 
molten  metal  in  the  cupel.  Sometimes  the  substance  is 
gradually  added,  by  means  of  a  small  iron  spoon  ;  but  it 
is  preferable  to  use  paper,  or  thin  lead,  as  just  recom- 
mended. 

When  the  cupels  are  filled,  the  furnace  is  closed,  either 
by  the  door  or  by  pieces  of  lighted  fuel,  so  that  the  fused 
metals  may  become  of  the  same  temperature  as  the  muffle. 
When  this  point  has  been  gained,  air  is  allowed  to  pass 
into  the  furnace ;  the  metallic  bath  is  then  in  the  state 
termed  uncovered ;  that  is,  it  presents  a  convex  surface, 
very  smooth  and  without  slag.  When  the  air  comes  in 
contact  with  it,  it  becomes  very  lustrous,  and  is  covered 
with  luminous  and  iridescent  patches,  which  move  on  the 
surface,  and  are  thrown  towards  the  sides.  These  spots 
are  occasioned  by  the  fused  oxide  of  lead  which  is  continu- 
ally forming,  and  which,  covering  the  bath  with  a  very 
thin  coating  of  variable  thickness,  presents  the  phenomenon 
of  coloured  rings. 

The  fused  litharge,  possessing  the  power  of  moistening 


558  THE   ASSAY    OF   SILVER. 

(so  to  speak)  the  cupel,  is  rapidly  absorbed  by  it  when 
sufficiently  porous,  so  that  the  metallic  alloy  is  covered 
and  uncovered  .every  instant,  which  establishes  on  its  sur- 
face a  continual  motion  from  the  centre  to  the  circumfer- 
ence. At  the  same  time  a  vapour  rises  from  the  cupels 
which  fills  the  muffle,  and  is  produced  by  the  vapour  of 
lead  burning  in  the  atmosphere.  An  annular  spot  is  soon 
observed  on  the  cupel  around  the  metal,  and  this  spot 
increases  incessantly  until  it  has  reached  its  edges. 

In  proportion  as  the  operation  proceeds,  the  metallic 
bath  of  silver-lead  diminishes,  becoming  more  and  more 
rounded  ;  the  shining  points  with  which  it  is  covered 
become  larger  and  move  more  rapidly  ;  lastly,  as  the  whole 
of  the  lead  separates,  the  button  seems  agitated  by  a  rapid 
movement,  by  which  it  is  made  to  turn  on  its  axis ;  it 
becomes  very  lustrous,  and  presents  over  its  whole  surface 
all  the  tints  of  the  rainbow  :  suddenly  the  agitation  ceases, 
the  button  becomes  dull  and  immovable,  and  after  a  few 
instants  it  takes  the  look  of  pure  silver.  This  last  part  in 
the  operation  of  cupellation  is  termed  the  brightening, ful- 
guration,  or  coruscation. 

If  the  button  be  taken  from  the  muffle  directly  after 
the  brightening,  it  may  throw  off  portions  of  its  substance  ; 
this  must  be  avoided,  especially  when  the  button  is  large. 
The  button,  when  covered  by  mammillated  and  crystalline 
asperities,  is  said  to  have  'vegetated.'  The  cause  of  this 
effect  seems  to  be,  that  when  the  fused  buttons  are  suddenly 
exposed  to  the  cold  air,  the  silver  solidifies  on  the  surface, 
whilst  that  in  the  interior  remains  liquid.  The  solid  crust, 
contracted  by  cooling,  strongly  compresses  the  liquid 
interior,  which  opens  passages  for  itself,  through  which  it 
passes  out,  and  around  which  it  solidifies  when  in  contact 
with  the  cool  air.  But  it  sometimes  happens  that,  when 
the  contraction  is  very  strong,  a  small  portion  of  the  silver 
is  thrown  off  in  the  shape  of  grains,  which  are  lost. 

After  brightening,  the  cupels  must  be  left  for  a  few 
minutes  in  the  furnace,  and  drawn  gradually  to  the  mouth, 
before  they  are  taken  out,  so  that  the  cooling  may  be  slow 
and  gradual.  These  precautions  are  nearly  superfluous 


CUPELLATION.  659 

when  the  buttons  are  not  larger  than  the  head  of  an  ordi- 
nary pin. 

As  silver  is  sensibly  volatile,  it  is  essential,  in  order  that 
the  smallest  possible  quantity  be  lost,  to  make  the  cupel- 
lation  at  as  low  a  temperature  as  may  be.  On  the  other 
hand,  the  heat  ought  to  be  sufficiently  great,  so  that  the 
litharge  may  be  well  fused  and  absorbed  by  the  cupel ;  and, 
moreover,  if  the  temperature  be  too  low,  the  operation  lasts 
a  very  long  time,  and  the  loss  by  volatilisation  will  be  more 
considerable  than  if  the  assay  had  been  made  rapidly  at  a 
much  higher  temperature. 

Experience  has  proved  that  the  heat  is  too  great  when 
the  cupels  are  whitish  and  the  metallic  matter  they  contain 
can  scarcely  be  seen,  and  when  the  fume  is  scarcely  visible 
and  rises  rapidly  to  the  arch  of  the  muffle.  On  the  contrary, 
the  heat  is  not  strong  enough  when  the  smoke  is  thick  and 
heavy,  falling  in  the  muffle,  and  when  the  litharge  can  be 
seen  not  liquid  enough  to  be  absorbed,  forming  lumps  and 
scales  about  the  assay.  When  the  degree  of  heat  is  suitable 
the  cupel  is  red,  and  the  fused  metal  very  luminous  and 
clear. 

In  general,  it  is  good  to  give  a  strong  heat  at  the  com- 
mencement, so  as  to  well  uncover  the  bath,  then  to  cool 
down,  and  increase  the  heat  at  the  end  of  the  operation  for 
a  few  minutes,  in  order  to  aid  the  brightening.  There  can 
be  no  inconvenience  in  urging  the  temperature  at  first,  be- 
cause the  silver-lead  is  then  poor,  and  much  precious  metal 
cannot  be  lost  by  volatilisation.  The  increase  of  fire  given 
towards  the  end  is  for  the  purpose  of  separating  the  last 
traces  of  lead,  from  which  it  is  very  difficult  to  free  the 
silver,  but  this  strong  fire  must  not  be  continued  long, 
otherwise  there  might  be  a  notable  loss  by  volatilisation. 
When  the  assay  of  very  poor  argentiferous  matters  is  made, 
the  heat  can  be  kept  up  nearly  all  through  the  cupellation. 
It  generally  succeeds  better  when  the  temperature  is  too 
high  than  too  low. 

The  force  of  the  current  of  air  which  passes  through 
the  muffle  is  another  very  important  thing  in  the  success 
of  the  operation.  Too  strong  a  current  cools  the  cupel, 


560  THE   ASSAY   OF    SILVER. 

oxidises  too  rapidly,  and  the  assay  would  be  spoilt.  With 
too  feeble  a  current  the  operation  proceeds  slowly,  the 
assay  remains  a  long  time  in  the  fire,  and  much  silver  is 
lost  by  volatilisation. 

When  the  litharge  is  produced  more  rapidly  than  it 
can  be  absorbed  by  the  cupel,  or  when  it  is  not  liquid 
enough,  which  may  happen  from  the  furnace  being  too 
cold,  or  when  other  oxides,  produced  at  the  same  time, 
diminish  its  fusibility,  it  accumulates  gradually  on  the  fluid 
metal,  forming  at  first  a  ring  which  envelopes  its  circum- 
ference, and  which,  gradually  extending,  covers  the  whole 
surface  ;  at  this  period  the  assay  becomes  dull,  and  all 
movement  ceases.  When  the  operation  is  carefully  at- 
tended to,  it  is  nearly  always  possible  to  avoid  this  acci- 
dent. If  at  the  first  moment  any  signs  are  manifested  of 
this  evil,  the  temperature  of  the  muffle  must  be  raised, 
either  by  shutting  the  door,  or  placing  in  it  burning  fuel ; 
the  assay  will,  in  a  little  time,  resume  its  ordinary  course. 
But  when  the  cause  of  the  mishap  is  supposed  to  be  the 
abundance  of  foreign  oxides  in  the  assay,  a  fresh  proportion 
of  lead  must  be  added. 

It  can  be  ascertained  whether  an  assay  has  passed  well 
by  the  aspect  of  the  button.  It  ought  to  be  well  rounded, 
white,  and  clear,  to  be  crystalline  below,  and  readily  de- 
tached from  the  cupel.  When  it  retains  lead  it  is  brilliant 
below  and  livid  above,  and  does  not  adhere  at  all  to  the 
cupel. 

In  order  to  detach  the  button,  seize  it  with  a  strong 
pair  of  pliers  (see  fig.  97),  and  examine  with  a  microscope, 
(see  fig.  98),  brushing  it  to  detach  small  particles  of 
litharge  which  may  adhere  to  it,  and  place  it  in  the  pan 
of  a  balance  (fig.  13.  page  24),  which  will  indicate  the 
y-J^th  of  a  grain.  The  weight  of  the  silver  furnished  by 
the  lead  or  litharge  employed  in  the  operation  ought  to 
be  subtracted  from  the  amount  of  silver  obtained  ;  so  that 
it  is  necessary  to  ascertain  the  richness  of  these  matters 
beforehand,  as  they  are  never  completely  free  from  silver. 
The  poorest  of  them  contain  from  y^oVoo-th  to  Tolroo^h- 

Sometimes  an  equal  quantity  of  lead  is  placed  in  another 


CUPELLATION.  561 

cupel,  and  the  silver  thus  obtained  placed  in  the  balance- 
pan  containing  the  weights. 

Cupellation  does  not  give  the  exact  proportion  of  silver 
contained  in  an  alloy.  There  is  always  a  loss,  and  this  loss 
is  always  greater  than  that  which  takes  place  in  the  large 
way,  as  in  the  latter  process  a  greater  quantity  is  always 

FIG.  t>7.  FIG.  98. 


obtained  than  that  determined  by  the  assay.  The  loss  of 
silver  is  traceable  to  three  causes  :  1st,  to  volatilisation  ; 
2ndly,  to  oxidation  ;  ordly,  and  lastly,  to  the  absorption  of 
minute  globules  of  silver  into  the  body  of  the  cupel.  It  is 
certain  volatilisation  takes  place,  because  a  notable  quan- 
tity of  silver  is  always  found  deposited  on  the  sides  of  the 
furnace  and  chimney  in  the  shape  of  dust ;  and  silver,  which 
is  volatile  by  itself,  becomes  much  more  so  when  alloyed 
with  lead,  and  is  carried  away  by  the  vapours  of  the  latter, 
and  found  in  the  pulverulent  deposits,  termed  lead  smoke 
or  fume,  which  proceed  from  the  combustion  of  the  latter 

o  o 


562  THE    ASSAY   OF    SILVER. 

metal  in  the  air.  Nevertheless,  this  cause  of  loss  is  not 
very  important,  for  it  is  rare  that  the  fume  contains  more 
than  To7ro~oth  °^  s^ver?  an^  accurate  experiments  have 
proved  that  in  cupellation  in  the  small  way  not  more  than 
two  to  three  per  cent,  of  .lead"  is  volatilised.  It  is  certain 
that  a  portion  of  the  silver  found  in  cupels  which  have 
been  used  for  assays  exist  in  the  state  of  oxide,  for  no  part 
of  their  mass  is  free — it  is  found  even  in  the  bottom  ; 
besides  it  is  known  that  the  lead  carbonate  precipitated 
from  lead  acetate  made  from  litharge  contains  silver,  and  a 
notable  quantity  of  that  metal  is  found  even  in  the  lead 
sulphate  prepared  by  means  of  alum  from  the  acetate 
(unless  the  sulphate  is  repeatedly  washed  with  water). 

It  has  been  remarked  .that  the  centres  of  cupels  which 
have  been  used  for  assays  are  richer  in  silver  than  the  parts 
near  the  circumference,  and  that  under  the  button  there  is 
a  spot  of  bright  yellow,  which  appears  to  be  a  compound 
of  silver.  But  the  most  important  cause  of  loss  in  an  assay 
is. the  property  which  the  alloys  of  silver  and  lead  possess 
of  introducing  themselves  into  the  pores  of  the  cupel.  The 
quantity  thus  lost  is  in  proportion  to  the  coarseness  of  the 
cupel.  For  the  same  quantity  of  silver,  the  loss  which 
takes  place  in  an  assay  varies  according  to  the  nature  of 
the  alloy,  and  the  circumstances  under  which  the  assay  is 
made ;  so  that  it  is  not  possible  to  form  accurate  tables  of 
correction.  This  loss  is  much  augmented  with  the  quantity 
of  lead  employed,  but  without  its  being  proportionate  ;  so 
that  when  scorification  is  had  recourse  to,  it  is  advantageous 
to  continue  the  operation  for  some  length  of  time,  in  order 
that  the  metallic  button  may  be  reduced  to  the  smallest 
suitable  volume. 

In  the  assay  of  rich  alloys,  the  proportion  to  the  total 
amount  of  silver  is  very  small,  but  notable  ;  and  it  has 
been  calculated  for  the  alloys  of  copper  employed  in  the 
arts  at  g^^th  ;  but  in  the  assay  of  poor  ores,  such  as 
galena  and  other  minerals  treated  in  the  large  way,  the 
loss  is  very  great,  for  it  is  usually  as  high  as  5-^0 th. 

By  extracting  the  lead  from  cupels  used  in  this  class 
of  assay,  the  metal  furnished  contains  from  about 


CUPELLATION.  563 

to  5  o  0To  o  o tn  °f  silver.  The  following  experiment  will 
give  an  idea  of  the  influence  of  the  proportion  of  lead  on 
the  loss  of  silver :  100  grains  of  commercial  litharge  were 
fused  with  10  grains  of  black  flux,  and  gave  27  grains  of 
lead,  and  a  slag ;  this  was  pulverised  and  reduced  in  the 
same  crucible  with  15  grains  of  black  flux,  and  a  second 
button  was*  produced  weighing  45  grains.  These ,  two 
buttons  being  cupelled  separately,  gave,  the  first  -0035 
and  the  second  *001  only  of  silver.  Three  new  quantities 
of  100  grains  of  the  same  litharge  were  fused ;  the  first 
with  \  a  part  of  starch,  the  second  with  2^,  and  the  third 
with  10  of  the  same  reducing  agent.  The  resulting 
buttons  of  lead  weighed  respectively  5,  28,  and  79  grains. 
These  buttons  were  cupelled,  and  furnished  -0035,  -0035, 
and  -003  respectively.  From  these  experiments  it  will  be 
seen  that  when  the  litharge  is  not  reduced  completely, 
there  remains  a  notable  proportion  of  silver  in  the  scoriae ; 
but,  nevertheless,  in  order  to  extract  the  largest  possible 
quantity,  the  whole  must  not  be  reduced.  Indeed,  but  a 
twentieth  part  only  need  be  reduced,  because  more  precious 
metal  is  lost  in  the  cupellation  of  a  large  quantity  of  lead 
than  remains  in  the  portion  not  reduced.  The  loss  of 
silver  in  large  cupellations  is  less  than  that  which  takes 
place  in  an  assay,  because  in  the  large  way  the  litharge, 
or  the  greater  part  of  it,  is  run  off;  whilst  in  an  assay  the 
cupel  totally  absorbs  it,  so  that  the  latter  presents,  rela- 
tively to  the  same  mass  of  lead,  a  very  much  smaller 
surface  in  the  large  than  in  the  small  way ;  now  it  can  be 
readily  seen  that  the  quantity  of  silver  lost  by  absorption 
into  the  pores  of  the  cupel  must  be  proportioned  to  its 
surface,  all  things  being  equal. 

It  has  been  ascertained  by  experiment  that  a  cupel 
absorbs  about  its  own  weight  of  litharge ;  so  that  from 
this  fact  a  cupel  of  the  proper  size  may  be  chosen,  when 
the  weight  of  lead  to  be  cupelled  is  ascertained.  It  is 
always  better  to  have  the  cupel  about  \  or  \  as  heavy 
again  as  the  lead  to  be  cupelled. 

The  various  metals  found  in  an  alloy,  which  can  be 
submitted  to  cupellation,  scorify  in  proportion  to  their 

o  o   2 


564  THE    ASSAY   OF   SILVER. 

oxidisability.  Those  most  oxidisable  scorify  with  the 
greatest  rapidity,  and  vice  versa  ;  so  that  those  which 
have  the  greatest  affinity  for  oxygen  accumulate  in  the 
first  portions  of  litharge  formed,  which,  by  that  means 
becoming  less  fusible,  sometimes  lose  the  property  of 
penetrating  the  cupel ;  hence  the  reason  why  cupellations 
always  present  more  difficulties  at  the  commencement  of 
the  operation  than  towards  the  end,  when  the  litharge 
formed  is  nearly  pure  lead  oxide,  and  can  contain  only 
copper  oxide. 

The  appearance  of  the  cupel  used  in  an  assay  will 
give  indications  of  the  metals  the  alloy  contained.  Pure 
lead  colours  the  cupel  straw-yellow,  verging  on  lemon- 
yellow.  Bismuth,  straw-yellow  passing  into  orange-yellow. 
Copper  gives  a  grey,  dirty  red,  or  brown,  according  to  its> 
proportion.  Iron  gives  black  scorise,  which  form  at  the 
commencement  of  the  operation,  and  are  generally  found 
at  the  circumference  of  the  cupel.  Tin  gives  a  grey  slag. 
Zinc  leaves  a  yellowish  ring  on  the  cupel,  producing  a 
very  luminous  flame,  and  occasioning  losses  by  carrying 
silver  in  its  vapour,  and  by  projecting  it  from  the  cupel 
in  its  ebullition.  Antimony  and  lead  sulphate  in  excess 
give  litharge-yellow  scoriae,  which  crack  the  cupel ;  but,, 
when  not  produced  in  too  great  a  proportion,  are  gradually 
absorbed  by  the  litharge.  If  the  lead  alloy  submitted  to 
cupellation  is  found  to  produce  this  effect,  a  fresh  portion 
must  be  mixed  with  its  own  weight  of  lead  and  scorified  : 
the  button  so  obtained  can  now  be  cupelled. 

Amalgamation. — There  are  a  certain  number  of  argen- 
tiferous matters  which  can  be  assayed  by  amalgamation y 
as  they  are  treated  in  the  large  way  by  that  method. 
Amongst  these  are  native  silver,  chlorides,  sulphides,  and 
arsenio-sulphides,  which  contain  neither  lead  nor  copper. 

But  this  process  is  seldom  had  recourse  to,  because 
it  is  long,  troublesome,  and  less  exact  than  those  just 
described. 


ASSAY   OF   THE   ALLOYS   OF   SILVER  AND    COPPER.          565 


Substances  of  the  Second  Class. 


Native  silver. 

Alloys  of  copper  and  silver. 

Alloys  of  other  metals  and  silver 

(artificial). 
Silver  antimonide. 
Silver  arsenide. 


Silver  telluride  (AgTe) 
Auriferous  silver  telluride  (see 

gold). 
Silver  hydrargyride  (amalgam), 

(Hg2Ag). 
Silver  auride  (see  gold). 


The  following  method  of  separating  silver  from  galena 
is  given  in  the  '  Chemical  News,'  vol.  ii.  p.  239. 

'  Galena  consists,  as  is  well  known,  of  lead  sulphide, 
mixed  with  a  variable  proportion  of  silver  sulphide,  and 
both  these  substances  fuse  together,  or  melt  at  a  bright 
red  heat.  Now,  it  so  happens  that,  when  silver  sulphide 
is  fused  with  lead  chloride,  what  is  called  a  double  decom- 
position takes  place  ;  that  is  to  say,  silver  chloride  and 
sulphide  of  lead  are  formed.  Consequently,  if  we  fuse 
together  a  quantity  of  argentiferous  galena  and  lead 
chloride,  we  shall  remove  the  whole  of  the  silver  from  the 
galena,  and  replace  it  by  lead  sulphide.  This,  then,  is  the 
process :  mix  together  the  galena  and  lead  chloride  in  the 
proportion  of  100  Ibs.  of  galena,  1  Ib.  of  lead  chloride, 
and  10  Ibs.  of  sodium  chloride  or  common  salt ;  or,  if  the 
galena  be  very  argentiferous,  add  a  larger  amount  of  lead 
chloride.  The  whole  is  then  fused  together,  when  the 
silver  chloride  and  common  salt  rise  to  the  surface,  and 
may  be  skimmed  off,  and  the  desilverised  galena  falls  and 
may  be  run  out  from  the  bottom.  The  mixture  of  silver 
chloride  and  salt  may  then  be  decomposed  by  lime  and 
charcoal,  or  in  any  other  manner  >  so  as  to  reduce  the  silver 
and  a  portion  of  the  surplus  lead  chloride,  by  which  a  metal- 
lic mass  will  result,  suitable  for  the  operation  of  the  cupel.' 

General  Remarks  on  the  Assay  of  the  Alloys  of  Silver 
and  Copper. — The  assay  of  these  alloys  is  nearly  always 
accomplished  (at  least  in  England)  by  cupellation.  This 
assay  is  most  important,  as  it  is  by  the  results  obtained  in 
the  manner  hereafter  described  that  the  price  or  value  of 
all  kinds  of  silver  bullion  is  determined. 

This  class  of  cupellation  is  effected  without  difficulty, 
because  the  copper  oxide  forms  so  slowly,  that  the  litharge 


566 


THE   ASSAY   OF   SILVER. 


is  always  enabled  to  pass  it  into  the  body  of  the  cupel. 
After  having  weighed  the  lead  and  placed  it  in  the  cupel, 
as  soon  as  it  is  perfectly  fused  place  in  it  the  alloy  to  be 
assayed,  wrapped  either  in  blotting-paper  or  thin  leaf-lead. 
It  is  essential,  in  this  class  of  assay,  to  employ  a  sufficient 
quantity  of  lead  to  carry  away  all  the  copper.  We  may 
always  be  sure  of  succeeding,  whatever  the  alloy  may  be, 
by  employing  the  maximum  proportion  of  lead,  that  is  to 
say,  the  quantity  necessary  to  pass  pure  copper ;  but  as 
the  loss  which  the  silver  undergoes  increases  with  the 
length  of  the  operation  and  with  the  mass  of  the  oxidised 
matters,  it  is  indispensable  to  reduce  this  loss  as  much  as 
possible  by  reducing  the  proportion  of  lead  to  that  which 
is  strictly  necessary.  Long  experience  has  proved  that 
silver  opposes  the  oxidation  of  copper  by  its  affinity,  so 
that  it  is  necessary  to  add  a  larger  amount  of  lead  in  pro- 
portion to  the  quantity  of  silver  present. 

M.  D'Arcet  has  obtained  the  following  results  by  the 
most  accurate  experiments  : — 


Standard  of 
silver 

Quantity  of 
copper  alloyed 

Quantity  of  lead 
necessary 

Eelation  of  lead 
to  copper 

1000 

0 

To*118 

950 

50 

3 

60  to  1 

900 

100 

7 

70  —  1 

800 

200 

10 

50  —  1 

700 

300 

12 

40  —  1 

600 

400 

14 

35  —  1 

500 

500 

16  to  17 

32  —  1 

400 

600 

16  —  17 

27  —  1 

300    - 

700 

16  —  17 

23  —  1 

200 

800 

16  —  17 

20  —  1 

100 

900                    16  —  17 

18  —  1 

pure  copper 

1000                    16  —  17 

16  —  1 

It  is  remarkable  that  below  the  standard  of  500,  the 
same  proportion  of  lead  must  be  employed,  whatever  that 
of  copper.  This  fact  is  repeatedly  verified  by  experiment. 
Whenever  fine  silver  is  fused  in  a  cupel,  it  is  always  neces- 
sary to  add  lead,  in  order  to  cause  the  button  to  unite 
and  form  well.  If  less  than  f\tns  °f  lead  be  employed, 
the  button  will  be  badly  formed  ;  the  litharge  cannot 
separate  but  by  the  action  of  a  very  strong  heat,  and  a 


ASSAY   OF   THE   ALLOYS   OF   SILVER   AND    COPPER. 


567 


considerable  loss  of  silver  ensues.  If,  on  the  contrary, 
y\ths  of  lead  is  exceeded,  the  cupellation  goes  on  well,  but 
the  loss  is  greater  on  account  of  the  duration  of  the  process. 
These  proportions  also  ought  to  vary  with  the  temperature. 
M.  Chaudet  has  found  that,  to  cupel  an  alloy  containing 
TroVns  °f  silver  >  5  parts  of  lead  are  required  in  the  mid- 
dle of  the  muffle,  10  in  the  front,  and  only  3  at  the  back. 
The  proportion  of  copper  carried  off  by  litharge  varies 
not  only  with  the  temperature,  but  even  for  the  same 
temperature  in  relation  to  the  amount  of  copper  and  lead 
the  alloy  contains.  By  cupelling  100  parts  of  copper  with 
different  proportions  of  lead  in  the  same  furnace,  M. 
Karsten  obtained  the  following  results  : — • 


Lead  added 

Copper  remaining  after 
cupellation 

Quantity  of  lead  consumed 
in  carrying  off  1  of  copper 

100 

78-75 

3- 

200 

70-12 

7-1 

300 

60-12 

7-7 

.       400 

49-40 

7-9 

500 

38-75 

8-1 

600 

26-25 

8-15 

700 

19-75 

8-00 

800 

8-75 

8-70 

900 

5-62 

9-50 

1000 

1-25 

10-10 

1050 

o-oo 

10-50 

From  which  we  see  that  the  lead  carried  away  from 
to  TVth  of  its  weight  of  copper.  Much  less  lead  can  be 
employed  in  a  cupellation  by  making  the  alloy  maintain 
its  richness  of  copper  throughout  the  operation.  This 
can  be  accomplished  by  adding  to  the  alloy  in  the  cupel 
small  doses  of  lead,  in  proportion  as  that  first  added  dis- 
appears by  oxidation.  If,  for  example,  an  alloy  composed 
of  4  parts  of  copper  and  one  of  silver  be  fused  with  10  of 
lead,  by  adding  successive  small  doses  of  the  latter,  as 
already  pointed  out,  but  7  parts  will  be  consumed,  although 
in  the  regular  way  from  16  to  17  would  be  employed. 

The  proportion  of  copper  oxide  contained  in  the  litharge 
increases  each  instant,  and  goes  on  incessantly  increasing 
when  an  alloy  of  copper  and  lead  is  cupelled  which  con- 
tains an  excess  of  copper.  According  to  M.  Karsten,  this 


508 


THE   ASSAY   OF   SILVER. 


proportion  is  always  about  13  per  cent,  at  the  commence- 
ment, and  36,  or  more  than  a  third,  at  the  end  of  the 
operation. 

In  the  assay  of  the  coined  alloys  of  copper  and  silver, 
the  loss  of  silver  may  even  amount  to  five  thousandths  ; 
but  the  loss  is  variable,  and  is  proportionally  greater  as 
the  standard  of  the  alloy  is  lower. 

The  following  Table  contains  the  results  of  many 
experiments  made  on  this  subject : — 


Exact  standard 

Standard  found  by  cupellation 

Loss,  or  the  quantity  of  fine 
metal  to  be  added  to  the  stan- 
dard as  obtained  by  cupellation 

1000 

998-97 

1-03 

975 

973-24 

1-76 

950 

947-50 

2-50 

925 

921-75 

3-25 

900 

896-00 

4-00 

875 

870-93 

4-07 

850 

845-85 

4-13 

825 

820-78 

4-22 

800 

795-70 

4-30 

775 

770-59 

4-41 

750 

745-38 

4-52 

725 

720-36 

4-64 

700 

695-25 

4-75 

675 

670-27 

4-73 

650 

645-29 

4-71 

625 

620-30 

4-70 

600 

595-32 

4-68 

575 

570-32 

4-68 

550 

545-32 

468 

525 

520-32 

4-68 

500 

495-32 

4-68 

475 

470-50 

4-50 

450 

445-69 

4-31 

425 

420-87 

4-13 

400 

396-05 

3-95 

375 

371-39 

3-61 

350 

346-73 

3-27 

325 

322-06 

2-94 

300 

297-40 

2-60 

275 

272-42 

2-68 

250 

247-44 

2-56 

225 

222-45 

2-55 

200 

197-47 

2-55 

175 

173-88 

2-12 

150 

148-30 

1-70 

125 

123-71 

1-29 

100 

H9-12 

0-88 

75 

7434 

0-66 

50 

49-56 

0-44 

25 

2478 

0-22 

ASSAY    PROPEK    OF    SILVER   BULLION.  569 

These  numbers,  however,, are  not  constant,  and  vary  with 
the  circumstances  under  which  the  assays  are  made :  two 
assays  made  from  the  same  ingot,  by  the  same  assayer, 
may  differ  as  much  as  four  or  five  thousandths.  Tillet 
has  remarked  that  the  cupels  can  retain  double  as  much 
silver  as  is  lost ;  which  proves,  as  has  already  been  men- 
tioned, that  the  silver  obtained  by  cupellation  is  not  per- 
fectly pure,  but  may  retain  as  much  as  1  per  cent,  of  lead. 

Special  Instructions  for  the  Assay  of  the  Alloys  of  Silver 
and  Copper. 

As  before  stated,  peculiar  weights  are  employed  in  the 
:assay  of  silver  bullion  ;  and  the  silver  assay  pound,  with 
its  divisions,  will  be  found  described  at  pages  31-32. 

In  the  '  General  Eemarks  on  the  Assay  of  the  Alloys  of 
Silver  and  Copper,'  it  will  be  seen  that  the  alloy  must  be 
cupelled  with  a  quantity  of  lead,  varying  with  the  amount 
•of  copper  present  in  the  alloy.  Standard  silver  cupels  very 
well  with  five  times  its  weight  of  lead  ;  but  when  the 
.approximative  quantity  of  alloy  present  is  not  known,  it 
must  be  determined  by  a  preliminary  assay. 

Assay  for  Approximative  Quantity  of  Alloy. — Weigh  off 
50  grains  of  pure  or  test  lead  ;  place  them  in  a  cupel 
previously  made  red-hot ;  when  the  lead  is  fused,  and  its 
'surface  covered  with  oxide,  place  in  it  by  means  of  the 
light  tongs  (a,  fig.  28,  page  66)  2  grains  of  the  alloy  under 
.assay,  wrapped  in  a  small  piece  of  thin  paper.  Allow  the 
•cupellation  to  go  on  according  to  the  instructions,  and  with 
.all  the  precautions  already  given,  and  when  complete, 
weigh  the  resulting  button,  and,  according  to  its  weight, 
.add  lead  in  the  actual  assay  in  the  quantity  that  is  suffi- 
cient, as  exhibited  in  the  Table  at  page  566. 

Assay  Proper  of  Silver  Bullion. — In  this  assay  the  ope- 
rator requires  silver  known  to  be  standard,  and  pure  lead. 
With  the  possession  of  the  above  substances  the  assay  is 
thus  proceeded  with  : — Place  the  12  grains  weight =1  lb., 
in  the  scale  pan,  and  exactly  counterbalance  it  with  stan- 
dard silver.  This  is  to  serve  as  a  check.  Eemove  the 
weight,  and  in  its  place  add  so  much  of  the  alloy  to  be 


570  THE   ASSAY   OF   SILVER. 

assayed  that  the  balance  is  again  equal.  In  one  cupel,  that 
destined  to  receive  the  check  sample,  place  60  grains  of  lead ; 
and  in  another  cupel  place  such  a  number  of  grains  of  lead 
as  may  be  found  necessary  by  the  preliminary  assay.  When 
the  lead  in  both  cupels  is  fused,  add  the  silver  alloy,  and 
cupel  with  the  necessary  precautions.  When  the  buttons  in 
the  cupels  are  cold,  seize  them  with  the  pliers,  and  if  neces- 
sary cleanse  them  w^ith  a  hard  brush,  and  place  one  in  each 
balance-pan.  If  they  exactly  balance  each  other,  the  alley 
operated  on  is  standard  silver  ;  if,  however,  it  weighs  less 
than  the  button  produced  from  the  check  sample  by  the 
weight  equivalent  to  2  pennyweights,  then  it  is  2  penny- 
weights worse  than  standard  :  on  the  other  hand,  if  it  be 
heavier  by  the  same  weight,  it  is  2  pennyweights  better  than 
standard.  Silver  is  also  reported  as  so  much  fine :  thus 
standard  silver  may  be  reported  as  11  ounces  2  penny- 
weights fine,  and  so  on.  In  case  extreme  accuracy  be  re- 
quired, correction  must  be  made  according  to  the  standard 
as  shown  by  the  Table  at  page  568.  The  standard  silver 
in  England  is  TV^o  ^ne- 

Assay  of  Alloys  of  Copper  and  Silver. — In  the  treat- 
ment on  the  large  scale  of  copper  ores  containing  silver,, 
the  contained  silver  is  found  alloyed  with  the  copper,  and 
it  often  falls  under  the  assayer's  province  to  determine  the 
quantity  of  precious  metal.  An  assay  of  this  kind  is  most 
conveniently  accomplished  by  scorification  before  cupel- 
lation,  thus  : — Prepare  four  scorifiers ;  weigh  into  each  of 
them  50  grains  of  the  alloy,  50  grains  of  fused  borax,  and 
600  grains  of  lead,  and  proceed  as  already  described  under 
the  head  '  Assay  of  Ores  of  the  First  Class  by  Scorifica- 
tion.' When  the  four  buttons  of  lead  are  obtained,  place 
them  together  in  another  scorifier,  and  submit  to  the 
furnace  until  the  contents  of  the  scorifier  are  completely 
covered  with  oxide;  pour  as  usual,  and  cupel  the  re- 
sulting mass  of  lead. 

Alloys  of  Platinum  and  Silver. — If  any  substance  con- 
taining platinum  as  well  as  silver  were  assayed  as  already 
described,  the  button  resulting  from  the  cupellation  would, 
in  addition  to  the  silver,  contain  the  whole  of  the  platinum. 


SEPAEATIXG    SILVER   FROM   THE   BASER   METALS.  571 

In    such  a  case  the    button    so    obtained    must  be  thus 
treated : — 

If  the  alloy  contain  much  platinum,  it  must  be  fused 
with  twice  its  weight  of  silver ;  then  treated  with  hot  nitric 
acid  ;  evaporate  the  solution  nearly  to  dryness  ;  add  water 
and  hydrochloric  acid,  until  no  further  precipitation  of 
silver  as  a  white  curdy  precipitate  (silver  chloride)  takes 
place.  The  silver  chloride  may  be  collected  either  on  a 
filter  or  by  decantation.  The  solution  containing  the 
platinum  is  treated  with  excess  of  sal-ammoniac  solution 
until  no  further  precipitation  takes  place ;  the  solution 
evaporated  to  dryness.  When  cold,  dilute  alcohol  is  added  ; 
and  the  insoluble  yellow  matter  (platinum  ammonio- 
chloride)  collected  on  a  filter,  washed  with  alcohol,  dried,, 
and  ignited.  The  ignited  residue  is  metallic  platinum, 
which  is  weighed.  The  loss  of  weight  which  the  alloy 
from  cupel  has  sustained  represents  the  amount  of  silver 
previously  alloyed  with  it. 

Alloy  of  Platinum,  Silver,  and  Copper. — Treat  such  an 
alloy  as  above  ;  and  the  liquid,  filtered  from  the  platinum 
ammonio-chloride,  will  contain  the  copper.  Acidulate  it 
with  hydrochloric  acid,  add  metallic  zinc,  and  proceed  as 
directed  under  the  head  '  Wet  Copper  Assay.' 

Native  Silver,  Rough  Silver  left  on  Sieve  during  Pulveri- 
sation of  Silver  Ores  of  First  Class,  and  Native  Alloys  of 
Silver — as  Antimonides,  $r. — are  treated  by  scorification 
and  cupellation  in  precisely  the  same  manner  as  just  de- 
scribed for  alloys  of  copper  and  silver. 

Dr.  W.  Dyce  proposed,  in  '  Tilloch's  Philosophical 
Magazine  '  for  1805,  the  following  process  for  separating 
gold  and  silver  from  the  baser  metals  : — 

4  Hitherto  the  process  has  always  been,  as  far  as  I  have 
understood  it,  attended  with  considerable  difficulty  in  the 
execution ;  but,  by  that  which  I  am  about  to  describe,  it 
is  done  with  exact  certainty.  It  was  discovered  and  com- 
municated to  me  by  a  gentleman  in  the  neighbourhood. 
The  process  consists  in  mixing  not  less  than  two  parts  of 
powdered  manganese  with  the  impure  or  compound  metal, 
which  should  be  previously  flattened  or  spread  out  so  a& 


-572  THE   ASSAY   OF   SILVER. 

to  expose  as  large  a  surface  as  possible,  and  broken  or  cut 
into  small  pieces  for  the  convenience  of  putting  the  whole 
into  a  crucible,  which  is  then  to  be  kept  in  a  sufficient 
heat  for  a  short  time.  On  removing  the  whole  from  the 
fire,  and  allowing  it  to  cool,  the  mixture  is  found  to  be 
-converted  into  a  brownish  powder,  which  powder  or  oxide 
is  then  to  be  mixed  with  an  equal  proportion  of  powdered 
glass,  and  then  submitted  in  a  crucible  to  a  sufficient  heat, 
so  as  to  fuse  the  whole,  when  the  perfect  metals  are 
found  at  the  bottom  in  a  state  of  extreme  purity,  a  cir- 
•cumstance  of  no  small  importance  to  the  artist  and  the 
chemist,  the  latter  of  whom  will  find  no  difficulty  in  sepa- 
rating the  one  from  the  other  with  so  little  trouble  com- 
pared with  the  usual  processes,  that  I. have  no  doubt  it 
will  always  be  practised  in  preference  to  the  cupel/ 

Assay  of  Silver  Bullion  by  the  Wet  Method. — From  that 
which  has  been  stated  under  the  head  of  '  Cupellation,'  it 
will  be  observed  that  there  are  many  sources  of  error  ; 
such  as  volatilisation  of  the  precious  metal,  its  oxidation 
in  the  presence  of  excess  of  lead  oxide  and  atmospheric 
oxygen,  and  lastly,  its  absorption  into  the  body  of  the 
cupel  either  as  oxide  or  metal,  or  in  both  states.  These 
losses,  as  before  stated,  vary  with  the  temperature,  the 
amount  of  lead  employed,  and  the  texture  of  the  cupel ; 
and,  as  may  be  seen  from  the  table  of  corrections  as 
drawn  up  by  D'Arcet,  give  a  very  erroneous  assay,  unless 
the  addition  necessary  for  each  standard  be  made. 

Considerable  attention  was  called  to  this  matter  in 
France  some  years  since,  and  a  Special  Commission  was 
appointed  to  examine  the  subject  thoroughly,  and,  if 
possible,  to  devise  some  means  of  assay  which  might  be 
both  easy  and  accurate.  The  result  of  this  examination 
was  the  invention  of  a  process  of  assay  at  once  elegant 
and  trustworthy  :  and  as  a  full  account  of  this  method  has 
not,  to  the  author's  knowledge,  been  translated  and  pub- 
lished in  this  country,*  he  has  prepared  the  present  from 
M.  Gay-Lussac's  Eeport,  which  formed  a  part  of  a  com- 

*  Some  portion  of  this  report  has  been  published  in  Dr.  Ure's  '  Dictionary 
of  Arts,  Mines,  and  Manufactures.' 


ASSAY   OF   SILVER   BULLION   IN   THE   WET   WAY. 

munication  from  M.  Thiers  to  Earl  Granville,  and  which 
appeared  in  the  original  language  in  the  year  1837,  in  a 
Eeport  on  the  Eoyal  Mint. 

The  process  of  assay  about  to  be  described  consists  in 
determining  the  fineness  of  silver  bullion  by  the  quantity 
of  a  standard  solution  of  common  salt  necessary  to  fully 
and  exactly  precipitate  the  silver  contained  in  a  known 
weight  of  alloy.  This  process  is  based  on  the  following 
principles : — 

The  alloy,  previously  dissolved  in  nitric  acid,  is  mixed 
with  a  standard  solution  of  common  salt,  which  precipi- 
tates the  silver  as  chloride,  a  compound  perfectly  insoluble 
in  water,  and  even  in  acids. 

The  quantity  of  silver  chloride  precipitated  is  deter- 
mined not  by  its  weight,  which  would  be  less  exact  and 
occupy  too  much  time,  but  by  the  weight  or  volume  of 
the  standard  solution  of  common  salt  necessary  to  exactly 
precipitate  the  silver  previously  dissolved  in  nitric  acid. 

The  term  of  complete  precipitation  of  the  silver  can  be 
readily  recognised  by  the  cessation  of  all  cloudiness  when 
the  salt  solution  is  gradually  poured  into  that  of  the 
nitrate  of  silver.  One  milligramme  of  that  metal  is  readily 
detected  in  150  grammes  of  liquid  ;  and  even  a  half  or  a 
quarter  of  a  milligramme  may  be  detected,  if  the  liquid 
be  perfectly  bright  before  the  addition  of  the  salt  solu- 
tion. 

By  violent  agitation  during  a  minute  or  two,  the  liquid, 
rendered  milky  by  the  precipitation  of  silver  chloride, 
becomes  sufficiently  bright  after  a  few  moments'  repose  to 
allow  of  the  effect  of  the  addition  of  half  a  milligramme  of 
silver  to  be  perceptible.  Filtration  of  the  liquid  is  more 
efficacious  than  agitation  ;  but  the  latter,  which  is  much 
more  rapid,  generally  suffices.  The  presence  of  copper, 
lead,  or  any  other  metal,  with  the  exception  of  mercury 
(the  presence  of  the  latter  metal  requires  a  slight  modifi- 
cation of  the  process,  which  will  be  hereafter  pointed  out), 
in  the  silver  solution,  has  no  sensible  influence  on  the 
quantity  of  salt  required  for  precipitation  :  in  other  words, 
the  same  quantity  of  silver,  pure  or  alloyed,  requires  for 


•574 


THE    ASSAY   OF    SILVER. 


FIG.  99. 


its  precipitation  a  constant  quantity  of  the  standard  salt 
solution. 

Supposing  that  1  gramme  of  pure  silver  be  the  quan- 
tity operated  on,  the  solution  of  salt  required  to  exactly 
precipitate  the  whole  of  the  silver  ought  to  be  of  such 
strength  that,  if  it  be  measured  by  weight,  it  shall  weigh 
exactly  100  grammes,  or  if  by  volume  100  cubic  centi- 
metres. This  quantity  of  salt  solution  is  divided  into 
1000  parts,  called  thousandths. 

The  standard  of  an  alloy  of  silver  is  generally  the 
number  of  thousandths  of  solution  of  salt  necessary  to 
precipitate  the  silver  contained  in  a  gramme  of  the  alloy. 

Measurement  of  the  Solution  of  Common  Salt. — The 
solution  of  common  salt  will  hereafter  be  termed  the 
normal  solution  of  common  salt.  It  can  be  measured  by 
weight  or  volume.  The  measure  by  weight  gives  greater 
precision,  and  it  has  the  special  advan- 
tage of  being  independent  of  temperature  ; 
but  it  requires  too  much  time  in  nume- 
rous assays.  The  measure  by  volume 
gives  a  sufficient  exactitude,  and  requires 
much  less  time  than  the  measure  by 
weight ;  it  is,  indeed,  liable  to  the  in- 
fluence of  temperature,  but  tables  for 
correction  will  be  appended. 

Measure  of  the  Normal  Solution  of 
Salt  by  Weight. — This  solution  should  be 
so  made  that  100  grammes  will  exactly 
precipitate  1  gramme  of  pure  silver 
dissolved  in  nitric  acid.  In  order  to 
point  out  the  method  of  taking  the 
weight  it  must  be  supposed  to  have 
been  previously  prepared.  After  the 
process  of  taking  the  weight  is  described, 
the  mode  of  preparing  the  solution  will 
be  given. 

The  solution  is  weighed  in  a  burette 
(fig.  99)  whose  capacity  is  from  115  to  120  grammes  of 
the  solution,  and  divided  into  grammes.  These  divisions  are 


MEASUREMENT   OP   THE   SOLUTION   OF   COMMON   SALT.       57o 

for  the  purpose  of  approximatively  determining  the  weight 
•of  solution,  so  as  to  shorten  the  operation  of  weighing.  The 
burette  is  represented  as  closed  by  a  cork,  B,  in  order  to 
prevent  evaporation  of  the  solution  when  the  instrument  is 
not  in  use.  It  is  also  easy  to  remedy  the  inconvenience  of 
evaporation,  by  rinsing  the  burette  with  a  small  quantity 
of  the  fresh  solution.  On  pouring  the  solution  from  the 
'Orifice,  0,  of  the  burette,  each  division  will  furnish  from 
8  to  10  drops ;  and  consequently  the  weight  of  a  drop  is 
about  a  decigramme.  The  burette  is  filled  with  solution 
to  the  division  o  ;  it  is  then  tared  in  a  balance  capable  of 
turning  with  a  centigramme.  The  burette  is  then  re- 
moved, and  its  place  supplied  with  a  weight  equivalent  to 
the  amount  of  solution  required — 100  grammes,  for  in- 
stance. The  solution  is  then  gradually  poured  from  the 
burette  into  a  bottle  appointed  for  its  reception,  until  the 
equilibrium  is  nearly  established.  It  is  not  easy  to  attain 
the  point  exactly,  as  no  smaller  quantity  than  a  drop  can 
be  poured  from  the  burette.  This,  however,  is  a  matter 
of  indifference ;  it  suffices  to  know  the  exact  weight  of 
the  solution  poured  out :  suppose  it  to  be  99  gr.  85  c. 
The  mode  of  more  nearly  approximating  the 
required  weight  of  100  grammes  will  now  be 
pointed  out. 

It  must  be  remarked  that  it  is  not  the 
amount  of  water  contained  in  the  100  grammes 
that  is  of  consequence,  but  only  the  quantity 
of  salt  found  in  solution ;  this  should  exactly 
represent  1000  thousandths  of  pure  silver.  If 
now  100  grammes  of  the  normal  solution  be 
mixed  with  900  grammes  of  water,  it  is  evi- 
dent that  1  gramme  of  this  new  solution  is 
equivalent  to  a  decigramme  of  the  first,  and 
consequently  it  will  be  easy  to  obtain  100 
grammes  of  the  normal  solution,  or  rather  the 
1000  thousandths  of  salt  it  ought  to  contain  ; 
it  will  now  be  sufficient  to  add  to  the  99 
grammes  already  poured  from  the  burette,  1^  gramme 
of  the  new  solution.  It  can  be  weighed,  like  the  normal 


576     .  THE   ASSAY    OF   SILVER. 

solution,  to  a  drop  nearly,  in  the  burette  (fig.  100),  of 
such  a  diameter  that  each  small  division  represents  a 
decigramme  of  liquid,  and  consequently  a  centigramme 
of  the  normal  solution ;  but  it  is  more  readily  measured 
by  volume,  preparing  it  in  the  manner  to  be  hereafter 
pointed  out.  To  avoid  all  confusion,  a  solution  to  be 
termed  a  decline  solution  of  common  salt  is  one  containing 
the  same  quantity  of  salt  as  the  normal  solution,  in  a 
weight  or  volume  ten  times  greater. 

A  decime  solution  of  silver  is  a  solution  of  silver  equi- 
valent to  the  latter,  both  mutually  suffering  complete 
decomposition. 

Preparation  of  the  Decime  Solution  of  Common  Salt. — 
One  hundred  grammes  of  the  normal  solution  of  common 

FIG.  101.  FIG.  102. 


salt  are  weighed  in  a  flask  (fig.  101)  containing  a  kilo- 
gramme of  pure  water,  when  filled  up  to  the  mark  a  b, 
or  1000  cubic  centimetres ;  this  quantity  is  made  up  witli 
pure  water,  taking  care  to  agitate  the  whole  well,  to 
render  the  mixture  homogeneous.  A  cubic  centimetre  of 
this  solution  represents  1  thousandth  of  silver.  This 
quantity  is  readily  obtained  by  means  of  a  pipette  (fig. 
102),  gauged  so  that  when  filled  up  with  water  to  the^ 
mark  c  d,  it  shall  allow  1  gramme,  or  1  cubic  centimetre, 
to  run  freely,  the  small  quantity  of  liquid  remaining  in 
the  pipette  not  forming  part  of  the  gramme.  In  pouring 
the  liquid  by  drops,  a  little  more  or  a  little  less  than 


PREPARATION    OF   THE   DECIME   SOLUTION    OF   SALT.         577 

twenty  may  be  counted,,  according  to  the  size  of  the 
orifice,  o.  This  number  will  not  vary  more  than  one 
drop.  Half  a  cubic  centimetre  will  consequently  be 
represented  by  10  drops,  and  a  quarter  by  5.  The  pre- 
cision arrived  at  by  this  method  of  measurement  suffices, 
since  the  possible  error  on  the  cubic  centimetre  will  be 
but  one-twentieth  of  that  quantity,  or  one-twentieth  of  a 
thousandth  ;  if,  however,  many  measures  be  required,  then 
compensation  must  be  made. 

The  decime  solution  of  common  salt  requisite  for  assays 
must  be  kept  in  a  bottle  (Fig.  102)  closed  by  a  cork,  tra- 
versed by  the  pipette,  firmly  fixed  in  a  FlG  103 
hole  bored  for  that  purpose.  To  mea- 
sure a  thousandth  with  the  pipette, 
the  bottle  is  held  with  one  hand,  and 
the  pipette  with  the  other  (Fig.  103). 
The  pipette  is  taken  from  the  solution 
after  its  upper  orifice  has  been  closed 
by  the  forefinger ;  the  lower  orifice 
is  then  inclined  against  the  edge'  of 
the  flask  to  remove  the  liquid,  which 
without  this  precaution  would  remain 
there  :  the  mark  c  d  is  then  raised  to 
the  level  of  the  eye,  and  by  a  suitable 
pressure  of  the  forefinger  on  the 
upper  orifice,  which  may  be  obtained  by  giving  the  pipette 
a  slight  alternating  circular  movement  between  the  fingers, 
the  solution  is  allowed  to  run  out  gradually.  The  instant 
the  concave  surface  of  the  liquid  is  at  the  level  c  d,  the 
pipette  is  firmly  closed  by  pressure  of  the  forefinger  on  its 
orifice,  which  is  held  above  the  bottle  into  which  the  solu- 
tion is  to  be  poured,  and  the  forefinger  removed  so  that  it 
can  be  emptied.  It  is  here  necessary  to  remark,  that  in 
order  to  regulate  the  slow  and  regular  runnings  of  the 
liquid  from  the  pipette,  by  the  pressure  of  the  forefinger, 
the  latter  ought  to  be  neither  too  moist  nor  too  dry  :  if  too 
dry  it  will  not  perfectly  close  the  orifice,  even  by  strong 
pressure  ;  if  too  moist,  it  prevents  the  entrance  of  air,  and 
the  liquid  will  not  run.  or  if  it  do,  it  will  be  irregularly. 

p  P 


578 


THE    ASSAY    OF    SILVER. 


This  observation  should  not  be  lost  sight  of  in  the  use  of 
the  large  burettes  mentioned  hereafter. 

Preparation  of  the  Decime  Solution  of  Silver. — The 
decime  solution  of  silver  is  prepared  by  dissolving  1 
gramme  of  pure  silver  in  nitric  acid,  in  a  flask  holding  1 
litre  (see  Fig.  101),  and  then  diluting  the  solution  with 
distilled  water,  so  that,  cooled  at  the  ordinary  temperature 

FIG.  lOi. 


of  the  air,  it  shall  occupy  exactly  the  volume  of  one  litre. 
It  is  measured  in  precisely  the  same  manner  as  the  decime 
salt  solution. 

Weighing  the  Normal  Solution  of  Common  Salt. — To 
execute  this  operation  with  rapidity,  a  balance  similar  to 
that  represented  at  Fig.  104  is  employed.  The  arms  are 
divided  as  in  the  assay  balance  described  at  p.  25  ;  each 
of  the  arms,  c  B  and  c  B,  are  furnished  with  a  rider,  c,  of 
such  a  weight  (about  5  decigrammes)  that  moved  from  the 
right  or  the  left  of  the  centre,  c,  of  each  arm,  it  indicates 


PREPARATION   OF   THE   NORMAL    SALT   SOLUTION.  579 

two  decigrammes.  The  space  traversed  by  the  rider  is 
divided  into  twenty  equal  parts,  representing  an  equal 
number  of  centigrammes. 

We  will  take  for  example  the  weighing  of  100  grammes 
of  normal  solution  of  common  salt,  which  is  that  most  fre- 
quently made  in  the  determination  of  the  standard  of  all 
varieties  of  argentiferous  matter. 

There  are  two  weights,  one,  P,  equal  to  the  tare  of  the 
burette  when  fall  of  solution  to  the  mark  0,  the  other,  P', 
equals  100  grammes.  The  burette  is  filled  with  solution, 
and  placed  on  the  right-hand  pan  of  the  balance,  on  which 
it  is  kept  in  position  by  the  collar  d  e,  and  through  which 
it  is  passed  before  placing  it  on  the  pan.  The  tare,  P,  of 
the  burette  is  supposed  to  be  on  the  opposite  side.  If  the 
equilibrium  be  not  perfect,  it  is  effected  by  the  rider  on  the 
left ;  the  burette  is  then  removed,  and  100  grammes  of  the 
solution  (either  more  or  less  to  one  or  two  decigrammes) 
poured  out.  The  burette  is  then  again  placed  in  the 
balance,  with  the  100-gramme  weight  Pf9  the  upper  part 
of  which  is  slightly  concave  to  receive  the  bottom  of  the 
burette,  in  order  to  prevent  it  sliding  off.  The  equilibrium 
is  again  established  by  the  aid  of  the  rider  on  the  right. 
If,  for  instance,  it  is  found  necessary  to  remove  the  rider 
15  divisions  towards  B,  which  represents  15  centigrammes, 
the  weight  of  the  solution  poured  out  of  the  burette  will 
be  equal  to  100  gr.-(H5  gr.  =  99-85  gr.  If,  on  the  other 
hand,  it  is  necessary  to  move  the  rider  six  divisions  towards 
c,  the  weight  of  the  solution  will  be  100  gr.  -f  0-06 
gr.  =--100-06  gr. 

The  above  method  of  weighing  the  salt  solution 
appears  to  be  the  most  convenient  that  can  be  employed, 
although  it  is  not  very  expeditious.  Other  methods  of 
weighing  and  measuring  will  be  given  in  an  appendix  to 
this  article. 

Preparation  of  the  Normal  Solution  of  Common  Salt 
when  measured  by  weight. — After  having  pointed  out  the 
method  of  weighing  the  normal  solution  of  salt,  and  of 
taking  very  small  quantities,  its  preparation  will  be 
described. 

p  p  2 


580  THE   ASSAY   OF   SILVER. 

Supposing  the  salt  as  well  as  the  water  to  be  employed 
are  pure,  the  two  substances  have  only  to  be  taken  in  the 
following  proportions  : — 0-5427  kilogramme  of  salt  and 
99-4573  kilogrammes  of  water,  to  form  100  kilogrammes- 
of  solution,  of  which  100  grammes  will  exactly  precipitate 
1  gramme  of  silver.  But  instead  of  pure  salt,  which  is- 
difficult  to  procure,  and  which  besides  rapidly  alters  by 
the  absorption  of  atmospheric  moisture,  it  is  preferable  to 
employ  a  concentrated  solution  of  commercial  salt,  which 
can  be  prepared  in  large  quantities,  and  kept  for  use  as 
needed.  The  quantity  of  salt  it  contains  can  be  ascer- 
tained by  evaporating  a  portion  to  dryness,  and  by  a  few 
experiments  it  is  easy  to  determine  in  what  proportion  it 
shall  be  mixed  with  water  to  produce  a  solution,  100 
FIG  105  grammes  of  which  shall  exactly  precipitate 
1  gramme  of  silver. 

Suppose,  for  example,  that  the  salt 
solution  contains  250  grammes  of  salt  per 
kilogramme,  and  that  it  is  necessary  to 
prepare  100  kilogrammes  of  the  normal 
solution.  Now,  since  for  the  preparation 
of  this  quantity  0-5427  kilogramme  of  pure 
salt  is  required,  we  have  the  following  pro- 
portion : — 

0-250  :  1   ::   0*5427    :    x  =  2-1708  kilogs. 

To  this  last  weight  enough  water  is  added 
to  make  up  100  kilogrammes,  that  is  to  say, 
97-8292  kilogrammes,  which  quantity  can 
be  readily  measured  by  means  of  a  flask 
containing  5  or  6  kilogrammes  previously 
gauged. 

The  mixture  must  be  well  agitated  by 
means  of  the  agitator  (Fig.  107),  which  is 
made  of  an  osier  twig,  split  into  four 
branches,  to  the  extremities  of  which  is  attached  a  small 
square  piece  of  silk.  This  substance  is  employed  to  avoid 
the  separation  of  filaments  which  would  ensue  from  the 
use  of  any  other  material.  This  agitator  can  be  intro- 


PREPARATION    OF   THE   NORMAL    SALT   SOLUTION.  681 

duced  into  very  small  openings,  and  is  exceedingly  ser- 
viceable in  agitating  large  masses  of  liquid. 

When  well  mixed,  the  solution  must  be  assayed.  To 
effect  this,  dissolve  1  gramme  of  silver  in  nitric  acid,  sp. 
gr.  1*290,  in  a  stoppered  bottle  (Fig.  106)  FlG  106 
holding  about  200  grammes  of  water,  tare 
the  burette  (Fig.  99)  filled  with  the  solution, 
and  pour  rather  more  than  less  into  the 
bottle ;  in  proportion  as  the  salt  employed  is 
impure,  more  than  100  grammes  will  be  re- 
quired to  precipitate  1  gramme  of  silver.  The 
mixture  is  at  first  milky,  but,  by  vigorously 
shaking  the  bottle,  having  its  stopper  firmly 
fixed,  for  about  a  minute,  and  then  allowing  it 
to  remain  at  rest  for  a  short  time,  the  liquid  will  become 
perfectly  bright :  two  drops  of  the  solution  must  then  be 
poured  into  it  from  the  burette  :  if  a  cloudiness  is  pro- 
duced, it  is  agitated  again  to  brighten  it,  and  two  drops 
more  added.  This  must  be  continued  until  the  last  two 
drops  added  give  no  precipitate.  The  operation  is  then 
terminated,  and  nothing  remains  to  state  but  the  result. 

Supposing  the  total  weight  of  solution  poured  from  the 
burette  is  101-880  grammes,  the  last  two  drops  must  not 
t>e  reckoned,  because  they  produce  no  effect ;  the  two  pre- 
ceding drops  were  necessary,  but  in  part  only ;  that  is 
to  say,  the  number  of  drops  to  be  deducted  is  less  than 
four,  and  more  than  two,  or  rather  it '  is  the  mean  term, 
three.  Or  the  weight  of  a  drop  can  be  known  exactly 
by  taking  that  of  a  dozen  :  suppose  it  is  equal  to  0-082 
gramme,  three  times  that  number  must  be  deducted, 
or  0-255  grammes  from  101*880  grammes  :  there  will 
remain  101-625  grammes,  representing  the  quantity  of 
normal  solution  necessary  to  precipitate  1  gramme  of 
silver. 

The  solution  is  thus  found  to  be  too  weak ;  to  bring  it 
to  its  proper  standard  it  is  necessary  to  remove  1*625 
gramme  of  water  from  the  101*625  grammes  of  solution, 
or,  what  is  the  same  thing,  to  add  to  the  normal  solution 
a  certain  quantity  of  the  concentrated  solution  of  common 


582  THE   ASSAY   OF   SILVER. 

salt,  which  quantity  may  be  found  by  the  following  pro- 


portion :  — 


100  :  1-625  ::  21708  kilogrs.  of  silver  solution  :  x  =  0-0353. 

After  the  addition  of  this  quantity  of  salt  to  the  normal 
solution,  a  fresh  assay  is  made,  proceeding  in  precisely  the 
same  manner  as  before  ;  taking  care,  however,  to  pour 
from  the  burette  a  weight  of  solution  slightly  under  100 
grammes,  or  1000  decigrammes  ;  for  instance,  998*4 
decigrammes,  because  it  is  not  possible,  in  pouring  the 
solution  by  drops,  to-  arrive  at  the  exact  weight,  1000 
decigrammes.  To  ascertain  the  true  standard  in  the  most 
exact  manner  possible,  a  decime  solution  must  be  prepared 
by  weighing  100  grammes  of  the  normal  solution,  and 
diluting  it  with  pure  water,  so  that  it  shall  occupy  one 
litre  :  a  cubic  centimetre  of  this  solution  will  represent  a 
decigramme  of  the  normal  solution.  This  decime  solution 
will  not  be  rigorously  exact,  since  the  normal  solution  has 
not  been  truly  standardised  ;  but  it  is  easily  perceived 
that  the  error  thus  committed  is  very  small,  and  that  it 
may  be  neglected.  Nevertheless,  as  soon  as  the  normal 
solution  is  perfectly  standardised,  it  is  better  to  prepare 
another  decime  solution. 

A  decime  solution  may  be  immediately  obtained  by 
dissolving  0-5427  gramme  of  pure  sea-salt  in  such  a  quan- 
tity of  water  that  the  whole  will  occupy  one  litre  ;  yet 
the  first  process  is  preferable. 

With  the  decime  solution  the  assay  may  be  thus  con- 
tinued, remembering  that  the  pipette  described  at  Fig.  102, 
is  a  cubic  centimetre  containing  20  drops  ;  that  the  half, 
therefore,  is  represented  by  10  drops,  and  the  fourth  by  5. 

To  the  998-4  decigrammes  of  normal  solution  already 
added,  pour  one  pipette  and  12  drops  of  the  decime 
solution,  which  will  exactly  complete  the  weight  of  1000 
decigrammes  of  normal  solution.  The  mixture  is  agitated 
to  brighten  it,  and  one-thousandth  of  common  salt  or  one 
pipette  of  the  decime  solution  added.  If  this  causes  a 
cloudiness,  it  is  agitated  and  a  second  thousandth  added. 
This  last  should  produce  no  opalescence.  The  weight  of 


PREPARATION   OF   THE   NORMAL   SALT  SOLUTION.  583 

normal  solution  necessary  to  exactly  precipitate  one 
gramme  of  silver  will  be  between  1000  and  1001  deci- 
grammes ;  that  is  to  say,  the  mean  will  be  equal  to  1000-5. 
The  standard  of  the  normal  solution  is  then  too  weak  by 
half  a  thousandth ;  to  correct  this  a  quantity  of  concen- 
trated salt  solution  must  be  added  equal  to  half  a  thou- 
sandth of  that  already  added  (2-1708  +  0-0353  =  2-2061 
kilogrammes)  ;  that  is  to  say,  1*1  gramme. 

A  new  assay  is  then  made  for  verification. 

When  the  standard  of  a  solution  is  very  nearly  arrived 
at,  it  is  well  to  employ  filtration  to  detect  the  slightest 
opalescence,  at  least  when  sufficient  time  is  not  allowed  for 
the  liquid  to  become  perfectly  bright.  The  surest  method 
when  the  standard  is  nearly  attained,  is  to  place  some  of 
the  liquid  in  two  test  glasses,  and  pour  into  one  a  few 
drops  of  the  decime  solution  of  common  salt,  and  into  the 
other  a  corresponding  number  of  drops  of  the  decime 
solution  of  silver  nitrate.  It  may  then  be  determined  on 
which  side  the  opalescence  is  manifested,  and  the  assay  of 
the  normal  solution  may  be  continued  after  the  mixture  of 
the  liquid  in  the  two  glasses,  since  the  two  quantities  of 
the  decime  solutions  of  common  salt  and  silver  nitrate 
mutually  decompose  each  other,  and  do  not  interfere  with 
the  assay.  Once  the  standard  of  the  normal  solution  is 
definitely  fixed,  the  sum  of  the  quantities  of  the  concen- 
trated solution  of  common  salt  which  have  been  employed, 
as  well  as  those  of  the  water,  must  be  noted,  and  in  the 
preparation  of  a  new  normal  solution  the  proportions 
found  as  above  would  only  have  to  be  mixed  to  obtain  at 
once  a  solution  having  very  nearly  its  true  standard. 

In  determining  the  standard  of  the  normal  solution, 
supposing  that  it  were  always  too  weak,  it  would  be 
necessary  to  add  to  the  solution  a  certain  quantity  of 
common  salt ;  but  if  the  true  amount  had  been  exceeded, 
and  it  had  been  found  too  strong,  the  solution  would  have 
to  be  precipitated  with  the  decime  solution  of  silver ;  and 
knowing  the  number  of  cubic  centimetres  or  thousandths 
of  silver  w^hich  had  been  necessary  to  precipitate  the 
excess  of  common  salt,  it  could  be  determined  what 


584  THE   ASSAY    OF    SILVER. 

amount  of  water  must  be  added  to  reduce  the  normal 
solution  to  standard.  For  instance,  if  2  thousandths  of  the 
decime  solution  of  silver  had  been  consumed,  2  thou- 
sandths of  its  weight  of  water  would  have  to  be  added  to 
the  total  amount  of  solution  ;  that  is  to  say,  0'2  kilo- 
gramme or  200  grammes. 

Preservation  of  the  Normal  Solution  of  Common  Salt. — 
The  most  suitable  vessel  for  containing  the  normal  solution 
of  common  salt  is  one  of  glass,  because  that  cannot  affect 
the  standard.  Large  glass  bottles,  termed  carboys,  are 
found  in  commerce.  These  bottles  cojitain  from  50  to  60 
litres,  and  are  very  applicable  for  this  purpose.  Fig.  107 
represents  one  of  these  bottles  fixed  in  a  stand  formed  of  a 
sieve  hoop.  It  is  graduated  into  litres  or  kilogrammes  of 
water,  and  a  paper  scale  fixed  on  its  side  shows  at  any 
time  the  quantity  of  contained  liquid.  It  is  closed  by  an 
hydraulic  valve,  made  of  sheet  iron,  but  the  bell  or  cover 
is  of  glass.  The  detail  of  this  valve  is  shown  at  Fig.  108. 
FIG.  107.  The  air  can  only  enter  the  bottle  by 

the  narrow  tube  T7,  and  cannot  pass 
out  by  it ;  consequently  evaporation 
is  not  to  be  feared.  The  neck  of 
the  valve  should  be  about  a  deci- 
metre deep,  into  which  mercury 
should  be  poured,  but  only  to  about 
one-third  of  its  height. 

The  solution  is  drawn  from  the 
bottle  by  the  syphon  S.  This  is 
furnished  with  a  stopcock ;  but  this 
syphon  being  brittle,  at  least  when 
not  of  metal,  is  not  convenient  in 
use,  since  it  is  incorporated  with  the 
bell  of  the  valve  :  it  is,  therefore, 
preferable  to  pierce  the  bottom  of 
the  bottle  (Fig.  109),  and  fix  a  metal  tube  (T)  by  means  of 
a  plate  moulded  on  the  bottom  and  cemented  to  it.  This 
tube  is  raised  a. little  above  the  bottom  of  the  bottle,  and 
covered  by  a  small  cup,  the  object  of  which  is  to  protect 
it  from  any  of  the  mercury  which  might  fall  into  it.  It  is 


APPLICATION    OF   GAY-LUSSAC'S    PROCESS. 


585 


terminated  at  its  other  extremity  by  a  very  narrow  tube, 
so  that  the  flow  of  the  solution  may  not  be  too  rapid. 


FIG.  108. 


FIG.  109. 


FIG.  110. 


Hereafter  a  metal  reservoir  will  be  described  which  has 
all  the  advantages  of  a  glass  vessel  without  its  inconve- 
niences. 

Application  of  the  Process  described  in  the  Determination 
of  the  Standard  of  a  Silver  Alloy. — The  alloy  is  supposed 
to  be  that  made  into  coin,  the  mean  standard 
of  which  is  fixed  at  900  thousandths,  but 
which  may  vary  from  897  to  903  thousandths 
without  ceasing  to  be  legal  (French  standard 
for  coin).  One  gramme  is  dissolved  in  the 
bottle  (fig.  106)  by  about  10  grammes  of 
nitric  acid,  sp.  gr.  1-290.  This  quantity  of 
nitric  acid  can  be  readily  taken  by  means  of 
the  pipette  P  (fig.  110),  which  contains  7'7 
grammes  of  water  to  the  mark  a  b.  The 
solution  may  be  accelerated  by  placing  the 
bottle  in  a  small  pan  of  hot  water,  the  bottom 
of  which  must  be  covered  with  a  piece  of 
cloth,  so  as  to  prevent  contact  of  the  glass  and  metal. 
"The  solution  finished,  and  the  flask  slightly  cooled,  the 


586  THE   ASSAY   OF   SILVER. 

nitrous  vapour  must  be  removed  by  a  blower  (see  fig.  Ill), 
the  nozzle  of  which  is  formed  of  a  piece  of  bent  glass  tube, 
connected  by  a  cork  with    a    copper  socket 
FIG.  111.      j}^   naving    a   screw   inside.     This   operation 
ought  to  be  effected,  as  well  as  the  solution 
of  the  alloy  in  nitric  acid,  under  a   chimney 
with  a  strong  current  of  air,  to  carry  off  the 
nitrous  vapour. 

The  burette  (fig.  99),  being  filled  with 
the  normal  solution  of  common  salt,  and 
tared,  about  90  grammes  are  poured  into  the 
solution  of  the  alloy  ;  say  89 -85  grammes. 
After  agitating  the  liquor,  a  cubic  centimetre 
of  the  decime  solution  of  common  salt  is  added 
representing  one-thousandth  of  silver.  If  a  cloudiness 
be  observed,  agitate  again,  and  add  a  second  thousandth 
of  common  salt,  and  so  on,  until  the  last  thousandth  gives 
no  precipitate.  Suppose  it  to  be  the  fourth :  that  must 
not  be  counted,  because  it  has  produced  no  effect;  and 
only  a  half  of  the  third  must  be  taken,  because  only  a 
portion  of  that  was  necessary.  The  standard  of  the  alloy 
would  be  consequently  equal  to  898'5  +  2-5  =  901. 

If  it  be  desirable  to  approach  still  nearer  to  the  true 
standard  of  the  alloy,  half-thousandths  must  be  added  until 
the  last  half-thousandth  gives  no  precipitate  ;  and  in  order 
to  avoid  all  confusion,  it  is  better  to  write  with  chalk  on 
a  blackboard  the  thousandths  of  common  salt,  preceding 
them  by  the  plus  sign  + ,  and  on  the  other  side  the  thou- 
sandths of  silver  nitrate,  preceding  them  by  the  sign  — 
minus. 

In  the  above  example,  after  the  addition  of  the  4 
thousandths  of  common  salt,  the  last  of  which  has  pro- 
duced no  cloudiness,  1^  thousandth  of  nitrate  of  silver  is 
added,  which  destroys  1^  thousandth  of  common  salt,  and 
brightens  the  liquid.  If  another  half-thousandth  of  nitrate 
of  silver  produce  no  precipitate,  it  is  not  taken  into  account, 
and  is  struck  off  from  the  table.  From  whence  it  is  con- 
cluded that  the  quantity  of  nitrate  of  silver  necessary  to 
destroy  the  excess  of  common  salt  is  more  than  1  and  less- 


APPLICATION   OF    GAY-LUSSAC'S   PROCESS.  58? 

than  li  ;  that  is  to  say,  nearly  the  i  of  a  thousandth,  and 
is  equal  to  1^.  Thus  the  number  of  thousandths  of  salt 
really  used  is  4  —  1-25  =  2-75.  The  standard  of  the  alloy, 
therefore,  is  898-50 +  2-75  =  901 -25. 

Another  example,  everything  else  remaining  as  above  : 
Suppose  the  first  thousandth  of  salt  did  not  precipitate. 
This  is  a  proof  that  too  much  normal  solution  of  common 
salt  has  been  employed,  and  that  there  is  an  excess  of  salt 
in  the  liquid.  Add  one-thousandth  of  silver,  and  agitate  : 
things  are  now  as  at  first,  but  it  is  nevertheless  known 
that  it  is  with  nitrate  of  silver  the  process  must  be  con- 
tinued. One- thousandth  has  been  added,  which  produced 
a  precipitate  ;  the  second  does  not.  The  standard  of  the 
alloy  is  consequently  898-5  —  0-5  =  898.  To  approach  still 
nearer  to  the  real  standard,  destroy  the  last  2  thousandths 
of  silver  by  2  thousandths  of  common  salt,  and  add  half  a 
thousandth  of  silver — a  cloudiness  is  produced,  as  already 
known  ;  but  another  half  thousandth  does  not  precipitate. 
The  standard  of  the  alloy  is  therefore  898^0—0-25  = 
898-25. 

This  process,  on  which  it  would  be  useless  to  enlarge 
further  at  present,  because  many  other  parts  of  the  pro- 
cess to  be  presently  described  apply  to  it,  is  general,  and 
gives  exactly  the  standard  of  an  alloy  when  it  is  known 
approximatively,  which  can  always  be  ascertained  by  a 
previous  rough  assay. 

Correction  of  the  Standard  of  the  Normal  Solution  of 
Salt  when  the  Temperature  Varies. — -'It  has  been  admitted 
that,  in  the  determination  of  the  standard  of  the  normal 
solution  of  salt,  the  temperature  has  remained  constant. 
Assays  made  under  these  circumstances  need  no  correc- 
tion ;  but  if  the  temperature  changes,  the  same  measure 
of  solution  will  not  contain  the  same  amount  of  salt.  Sup- 
posing the  solution  of  salt  has  been  standardised  at  15°. 
If,  at  the  time  an  experiment  is  made,  the  temperature 
is  18°,  for  instance,  the  solution  will  be  found  too  weak, 
since  it  has  become  expanded,  and  the  pipette  holds  less- 
than  its  weight.  If,  on  the  other  hand,  the  temperature 
falls  to  12°,  the  solution  becomes  concentrated,  and  ia 


538  THE   ASSAY   OF   SILVER. 

found  too  strong,  It  is  therefore  necessary  to  determine 
the  correction  to  be  made  for  any  variation  of  temperature 
that  may  occur. 

To  this  end  the  temperature  of  a  solution  of  common 
salt  has  been  gradually  raised  from  0....5....10....15....20.... 
2 5.... 30  degrees,  and  three  pipettefuls  of  the  solution 
exactly  weighed  at  each  of  the  above  temperatures.  One- 
third  of  the  total  weight  gives  the  mean  weight  of  the 
contents  of  a  pipette.  The  corresponding  weights  of  a 
pipetteful  of  solution  are  then  entered,  and  form  the  second 
column  of  the  following  table,  called  '  Table  of  Correction 
for  the  Variations  of  Temperature  in  the  Normal  Solution 
of  Salt.'  By  this  table  correction  may  be  made  for  any 
temperature  between  0  and  30  degrees,  when  the  solution 
•of  salt  has  been  standardised  within  the  same  limits.  Sup- 
pose, for  example,  the  solution  had  been  standardised  at 
15°,  and  that  at  the  time  it  was  used  its  temperature  was 
18°.  On  referring  to  the  second  column  of  the  table,  it 
will  be  seen  that  the  weight  of  a  measure  of  solution  at 
15°  is  100-099  gr. ;  and  at  18°  100-065  gr. ;  the  difference 
0-034  gr.  is  the  quantity  of  solution  taken  too  little,  and 
consequently  it  must  be  added  to  the  normal  measure,  so 
that  it  may  be  equal  to  one  thousand  thousandths.  If  the 
temperature  of  the  solution  had  fallen  to  10°,  the  differ- 
•ence  of  weight  between  a  measure  at  10°  and  a  measure  at 
15°  will  be  0*019  gr.,  which  must,  on  the  contrary,  be  de- 
ducted from  the  measure,  as  it  has  been  taken  in  excess. 
These  differences  of  weight  of  a  measure  of  solution  at  15°, 
and  that  of  a  measure  for  any  other  temperature,  form  the 
column  15°  in  the  table,  where -they  are  expressed  in  thou- 
sandths. They  are  written  on  the  same  horizontal  line  as  the 
temperatures  to  which  each  corresponds,  with  the  sign  -f- 
when  they  are  to  be  added,  and  the  sign  —  when  to  be 
subtracted.  The  columns  5°,  10°,  20°,  25°,  30°  have  been 
calculated  in  the  same  manner,  to  meet  cases  in  which  the 
normal  solution  had  been  graduated  at  each  of  the  above- 
named  temperatures.  Thus,  to  calculate  the  column  10°, 
take  the  number  100-118  from  the  column  of  weights  as 


CORRECTION   OF   THE   STANDARD    OF   SOLUTION    OF    SALT.      589 


a  point  of  departure,  and  find  the  difference  for  all  the 
other  numbers  in  the  same  column. 

An  application  of  this  Table  will  be  given  hereafter. 

TABLE  OF  CORRECTIONS  FOR  VARIATIONS  IN  TEMPERATURE  OF  THE  NORMAL. 

SALT  SOLUTION, 


Temperature 

Weight 

5° 

10° 

15° 

20° 

25° 

30° 

Degrees 

Grammes 

Mill. 

Mill. 

Mill. 

Mill. 

Mm. 

Mill. 

4 

100-109 

o-o 

-o-i 

+  0-1 

+  0-7 

4  17 

427 

5 

100-113 

o-o 

-0-1 

+0-1 

40-7 

4  17 

-"•2-8 

6 

100-115 

o-o 

00 

+  0-2 

+  0-8 

4  1-7 

42-8 

7 

100-118 

+  0-1 

o-o 

+  0-2 

+  0-8 

4  17 

42-8 

8 

100-120 

+  0-1 

o-o 

+  0-2 

+  0-8 

4  1-8 

42-8 

9 

100-120 

+  0'1 

o-o 

+  0-2 

+  0-8 

4  1-8 

42-8 

10 

100-118 

+0-1 

o-o 

+  0-2 

+  0-8 

4  17 

42-8 

11 

100-116 

o-o 

00 

+  0-2 

+  0-8 

+  17 

42-8 

12 

100-114 

o-o 

o-o 

+  0-2 

+  0-8 

4  17 

+  2-8 

13 

100-110 

o-o 

-0-1 

+  0-1 

+  0-7 

4  17 

+  27 

14 

100-106 

-0-1 

-o-i 

+  0-1 

4-0-7 

4  1-6 

427 

15 

100-099 

-0-1 

-0-2 

o-o 

40-6 

4  1-6 

+  2-6 

16 

100-090 

-0-2 

-0-3 

-0-1 

40-5 

4  1-5 

42-5 

17 

100-078 

-0-4 

-0-4 

-0-2 

40-4 

4  1-3 

42-4 

18 

100-065 

-0-5 

-0-5 

-0-3 

40-3 

4-1-2 

+  2-3 

19 

100-053 

-0-6 

-0-7 

-0-5 

40-1 

4  1-1 

422 

20 

100-039 

-0-7 

-0-8 

-0-6 

o-o 

4  1-0 

42-0 

21 

100-021 

-0-9 

-10 

-0-8 

-0-2 

+  0-8 

4  1-9 

22 

100-001 

-1-1 

-1-2 

-1-0 

-0-4 

40-6 

4  17 

23 

99-983 

-1-3 

-1-4 

-1-2 

-0-6 

40-4- 

4  1-5 

24 

99-964 

-1-5 

-1-5 

-1-4 

-0-8 

40-2 

4  1-3 

25 

99-944 

-1-7 

-1-7 

-1-6 

-1-0 

o-o 

4  1-1 

26 

99-924 

-1-9 

-1-9 

-1-8 

-1-2 

-0-2 

40-9 

27 

99-902 

-2-1 

-2-2 

-2-0 

-1-4 

-0-4 

407 

28 

99-879 

-2-3 

-2-4 

-2-2 

-1-6 

-07 

40-4 

29 

99-858 

-2-6 

-2-6 

-2-4 

-1«8 

-0-9 

+  0-2 

30 

99-836 

-2-8 

-2-8 

-2-6 

-2-0 

-1-1 

o-o 

TABLE  FOR  THE  ASSAY,  BY  THE  WET  METHOD,  OF  AN  ALLOY 
CONTAINING  ANY  PROPORTIONS  WHATEVER  OF  SILVER,  BY 
THE  EMPLOYMENT  OF  A  CONSTANT  MEASURE  OF  THE  NORMAL 
SOLUTION  OF  COMMON  SALT. 

The  process  by  which  the  normal  solution  of  salt  is 
measured  by  weight  is  applicable  to  the  assay  of  every 
kind  of  alloy,  since  it  suffices  to  take  a  weight  of  the  solu- 
tion corresponding  to  the  presumed  standard  of  the  silver, 
and  complete  the  assay  by  means  of  the  decime  solu- 
tion ;  the  process  by  volume,  however,  has  not  the  same 


590  THE   ASSAY   OF   SILVER. 

advantage,  because  the  volume  of  normal  solution  cannot 
be  varied  in  the  same  manner  as  the  weight.  This  incon- 
venience, however,  is  of  no  very  great  consequence,  for, 
by  keeping  the  volume  of  normal  solution  constant,  it 
suffices  to  vary  the  weight  of  the  alloy,  taking  in  each 
particular  case  a  weight  which  contains  approximatively 
one  gramme  of  pure  silver.  Suppose  the  alloy  has  a 
standard  of  about  900  thousandths,  we  have  the  following 
proportion : — 

900  thousandths  :  1000  of  alloy  :  :  1000  thousandths  : 

x  =  1111-1. 

If  that  weight  be  now  taken  to  ascertain  the  standard 
of  the  alloy,  it  may  be  found,  for  instance,  that  to  the  mea- 
sure of  1000  thousandths  of  salt  it  is  yet  necessary  to  add 
4  thousandths  of  salt  to  precipitate  the  whole  of  the  silver  ; 
that  is  to  say,  that  1111*1  of  alloy  really  contain  100'4  of 
silver.  From  this  result  the  real  standard  of  the  alloy  may 
be  found  to  be  90 3 '6,  by  the  following  equation : — 

1111-1  :  1004  : :  1000  :  x  =  903-6. 

But  such  calculations,  however  simple,  should  be 
avoided  where  numerous  daily  assays  are  made,  not  only 
on  account  of  the  time  consumed,  but  still  more  from  the 
errors  to  which  such  operations  are  necessarily  exposed. 
Fortunately,  all  these  inconveniences  may  be  avoided  by 
the  use  of  tables,  which  entirely  free  the  assay er  from 
calculation. 

Wishing  in  weighing  the  alloy  to  avoid  fractions  of 
thousandths,  and  only  making  use  of  tenths  and  half-tenths 
of  thousandths,  the  weight  of  alloy  increases,  starting  from 
a  gramme,  from  5  to  5  thousandths,  and  the  correspond- 
ing standard  for  each  of  these  weights  has  been  sought,  all 
containing  one  gramme  of  pure  silver.  Thus  the  weight 
1020  of  alloy,  in  which  there  are  1000  of  silver  and  20  of 
copper,  corresponds  to  the  standard  980-39,  obtained  by 
the  proportion — 

1020  :  1000  : :  1000  :  x  =  980-39. 


EXPLANATION   OP   THE    FOLLOWING   TABLES.  591 

On  this  principle  are  formed  the  first  and  second 
columns  of  the  table  marked  Salt.  The  first  contains  the 
weight  of  each  alloy,  and  the  second  its  corresponding 
standard.  The  following  columns,  1,  2,  o,  to  10,  give  the 
standard  of  the  alloy,  when,  instead  of  the  1000  milli- 
grammes of  silver  it  was  supposed  to  contain,  it  really 
contained  1,  2,  3,  &c.  more,  and  consequently  1,  2,  3,  &c. 
milligrammes  of  copper  less. 

Another  table,  constructed  in  the  same  manner  as  the 
preceding,  and  marked  Silver  Nitrate,  gives  the  standard 
of  the  alloy  when,  under  the  weight  given  in  the  first 
column,  it  contains  1,  2,  ,3,  &c.  milligrammes  less  silver, 
and  as  much  more  copper.  Thus,  for  example,  an  alloy  of 
the  weight  of  1020  (1000  silver  and  20  copper)  has  for  its 
standard  980-4  in  both  tables.  If  it  always  contains  in  the 
same  weight  4  more  silver  and  consequently  4  less  copper, 
its  standard  would  be  984-3,  and  would  be  found  in  the 
*  Salt '  table  at  the  intersection  of  the  column  4,  and  the 
horizontal  line  1020.  If,  on  the  contrary,  it  contains  4 
less  of  silver  and  4  more  of  copper,  its  standard  will  be 
976-5,  and  will  be  found  in  the  '  Silver  Nitrate '  table,  at 
the  intersection  of  the  column  4,  and  the  horizontal  line 
1020. 


592 


THE   ASSAY   OF   SILVER. 


Tables  for  Determining  the  Standard  of  any  Silver 
approximatively  containing 


SILVER 

Weight  of 

Assay  in 

0 

l 

2 

3 

4 

Milligrs. 

1000 

1000-0 

999-0 

998-0 

997-0 

996-0 

1005 

995-0 

994-0 

993-0 

992-0 

991-0 

1010 

990-1 

989-1 

988-1 

987-1 

986-1 

1015 

985-2 

984-2 

983-2 

982-3 

981-3 

1020 

980-4 

979-4 

978-4 

977-4 

976-5 

1025 

975-6 

974-6 

973-7 

972-7 

971-7 

1030 

970-9 

969-9 

968-9 

968-0 

967-0 

1035 

966-2 

965-2 

964-2 

963-3 

962-3 

1040 

961-5 

960-6 

959-6 

958-6 

957-7 

1045 

956-9 

956-0 

955-0 

954-1 

953-1 

1050 

952-4 

951-4 

950-5 

949-5 

948-6 

1055 

947-9 

946-9 

946-0 

945-0 

944-1 

1060 

943-4 

942-4 

941-5 

940-6 

939-6 

1065 

939-0 

938-0 

937-1 

936-1 

935-2 

1070 

934-6 

933-6 

932-7 

931-8 

930-8 

1075 

930-2 

929-3 

928-4 

927-4 

926-5 

1080 

925-9 

925-0  ' 

924-1 

923-1 

922-2 

1085 

921-7 

920-7 

919-8 

918-9 

918-0 

1090 

917-4 

916-5 

915-6 

914-7 

913-8 

1095 

913-2 

912-3 

911-4 

910-5 

909-6 

1100 

909-1 

908-2 

907-3 

906-4 

905-4 

1105 

905-0 

904-1 

903-2 

902-3 

901-4 

1110 

900-9 

900-0 

899-1 

898-2 

897-3 

1115 

896-9 

896-0 

895-1 

894-2 

893-3 

1120 

892-9 

892-0 

891-1 

890-2 

889-3 

1125 

888-9 

888-0 

887-1 

886-2 

885-3 

1130 

885-0 

884-1 

883-2 

882-3 

881-4 

1135 

881-1 

880-2 

879-3 

878-4 

877-5 

1140 

877-2 

876-3 

875-4 

874-6 

873-7 

1145 

873-4 

872-5 

871-6 

870-7 

869-9 

1150 

,869-6 

868-7 

867-8 

867-0 

866-1 

1155 

865-8 

864-9 

864-1 

863-2 

862-3 

1160 

862-1 

861-2 

860-3 

859-5 

858-6 

1165 

858-4 

857-5 

856-6 

855-8 

854-9 

1170 

854-7 

853-8 

853-0 

852-1 

851-3 

1175 

851-1 

850-2 

849-4 

848-5 

847-7 

1180 

847-5 

846-6 

845-8 

844-9 

844-1 

1185 

843-9 

843-0 

842-2 

841-3 

840-5 

THE   ASSAY   OF   SILVER. 


593 


Alloy  by  employing  an  Amount  of  Alloy  always 
the  same  Amount  of  Silver. 


NITRATE. 

5 

6 

7 

8 

9 

10 

995-0 

994-0 

993-0 

992-0 

991-0 

990-0 

990-0 

989-0 

988-1 

987-1 

986-1 

985-1 

985-1 

984-2 

983-2 

982-2 

981-2 

980-2 

980-3 

979-3 

978-3 

977-3 

976-4 

975-4 

975-5 

974-5 

973-5 

972-5 

971-6 

970-6 

970-7 

969-8 

968-8 

967-8 

966-8 

965-8 

966-0 

965-0 

964-1 

963-1 

962-1 

961-2 

961-3 

960-4 

959-4 

958-4 

957-5 

956-5 

956-7 

955-8 

954-8 

953-8 

952-9 

951-9 

952-1 

951-2 

950-2 

949-3 

948-3 

947-4 

947-6 

946-7 

945-7 

944-8 

943-8 

942-9 

943-1 

942-2 

941-2 

940-3 

939-3 

938-4 

938-7 

937-7 

936-8 

935-8 

934-9 

934-0 

934-3 

933-3 

932-4 

931-4 

930-5 

929-6 

929-9 

929-0 

928-0 

927-1 

926-2 

925-2 

925-6 

924-7 

923-7 

922-8 

921-9 

920-9 

921-3 

920-4 

919-4 

918-5 

917-6 

916-7 

917-0 

916-1 

915-2 

914-3 

913-4 

912-4 

912-8 

911-9 

911-0 

910-1 

909-2 

908-3 

908-7 

907-8 

906-8 

905-9 

905-0 

904-1 

904-5 

903-6 

902-7 

901-8 

900-9 

900-0 

900-4 

899-5 

898-6 

897-7 

896-8 

895-9 

896-4 

895-5 

894-6 

893-7 

892-8 

891-9 

892-4 

891-5 

890-6 

889-7 

888-8 

887-9 

888-4 

887-5 

886-6 

885-7 

884-8 

883-9 

884-4 

883-6 

882-7 

881-8 

880-9 

880-0 

880-5 

879-6 

878-8 

877-9 

877-0 

876-1 

876-7 

875-8 

874-9 

874-0 

873-1 

872-3 

872-8 

871-9 

871-0 

870-2 

869-3 

868-4 

869-0 

868-1 

867-2 

866-4 

865-5 

864-6 

865-2 

864-3 

863-5 

862-6 

861-7 

860-9 

861-5 

860-6 

859-7 

858-9 

858-0 

857-1 

857-8 

856-9 

856-0 

855-2 

854-3 

853-4 

854-1 

853-2 

852-4 

851-5 

850-6 

849-8 

850-4 

849-6 

848-7 

847-9 

847-0          846-1 

846-8 

846-0 

845-1 

844-3 

843-4          842-5 

843-2 

842-4 

841-5 

840-7 

839-8          839-0 

839-7 

838-8 

838-0 

837-1          836-3          835-4 

Q  Q 


594 


THE   ASSAY   OF   SILVER. 


SILVER 

Weight  of 
Assay  in 
Milligrs. 

0 

l 

2 

3 

4 

1190 

840-3 

849-5 

838-7 

837-8 

837-0 

1195 

836-8 

836-0 

835-1 

834-3 

833-5 

1200 

833-3 

832-5 

831-7 

830-8 

830-0 

1205 

829-9 

829-0 

828-2 

827-4 

826-6 

1210 

826-4 

825-6 

824-8 

824-0 

823-1 

1215 

823-0 

822-2 

821-4 

820-6 

819-7 

1220 

819-7 

818-8 

818-0 

817-2 

816-4 

1225 

816-3 

815-5 

814-7 

813-9 

813-1 

1230 

813-0 

812-2 

811-4 

810-6 

809-8 

1235 

809-7 

808-9 

808-1 

807-3 

806-5 

1240 

806-5 

805-6 

804-8 

804-0 

803-2 

1245 

803-2 

802-4 

801-6 

800-8 

800-0 

1250 

800-0 

799-2 

798-4 

797-6 

796-8 

1255 

796-8 

796-0 

795-2 

794-4 

793-6 

1260 

793-6 

792-9 

792-1 

791-3 

790-5 

1265 

790-5 

789-7 

788-9 

788-1 

787-3 

1270 

787-4 

786-6 

785-8 

785-0 

784-2 

1275 

784-3 

783-5 

782-7 

782-0 

781-2 

1280 

781-2 

780-5 

779-7 

778-9 

778-1 

1285 

778-2 

777-4 

776-6 

775-9 

775-1 

1290 

775-2 

774-4 

773-6 

772-9 

772-1 

1295 

772-2 

771-4 

770-7 

769-9 

769-1 

1300 

769-2 

768-5 

767-7 

766-9 

766-1 

1305 

766-3 

765-5 

764-7 

764-0 

763-2 

1310 

763-4 

762-6 

761-8 

761-1 

760-3 

1315 

760-5 

759-7 

758-9 

758-2 

757-4 

1320 

757-6 

756-8 

756-1 

755-3 

754-5 

1325 

754-7 

754-0 

753-2 

752-4 

751-7 

1330 

751-9 

751-1 

750-4 

749-6 

748-9 

1335 

749-1 

748-3 

747-6 

746-8 

746-1 

1340 

746-3 

745-5 

744-8 

744-0 

743-3 

1345 

743-5 

742-7 

742-0 

741-3 

740-5 

1350 

740-7 

740-0 

739-3 

738-5 

737-8 

1355 

738-0 

737-3 

736-5 

735-8 

735-1 

1360 

735-3 

734-6 

733-8 

733-1 

732-4 

1365 

732-6 

731-9 

731-1 

730-4 

729-7 

1370 

729-9 

729-2 

728-5 

727-7 

727-0 

1375 

727-3 

726-5 

725-8 

725-1 

724-4 

1380 

724-6 

723-9 

723-2 

722-5 

721-7 

1385 

722-0 

721-3 

720-6 

719-9 

719-1 

1390 

719-4 

718-7 

718-0 

717-3 

716-5 

1395 

716-8 

716-1 

715-4 

714-7 

714-0 

1400 

714-3 

713-6 

712-9 

712-1 

711-4 

THE   ASSAY   OF   SILVER. 


595 


NITRATE—  continued. 

0 

6 

7 

8 

9 

10 

836-1 

835-3 

834-5 

833-6 

832-8 

831-9 

832-6 

831-8 

831-0 

830-1 

829-3 

828-4 

829-2 

828-3 

827-5 

826-7 

825-8 

825-0 

825-7 

824-9 

824-1 

823-2 

822-4 

821-6 

822-3 

821-5 

820-7 

819-8 

819-0 

818-2 

818-9 

818-1 

817-3 

816-5 

815-6 

814-8 

815-6 

814-7 

813-9 

813-1 

812-3 

811-5 

812-2 

811-4 

810-6 

809-8 

809-0 

808-2 

808-9 

808-1 

807-3 

806-5 

805-7 

804-9 

805-7 

804-9 

804-0 

803-2 

802-4 

801-6 

802-4 

801-6 

800-8 

800-0 

799-2 

798-4 

799-2 

798-4 

797-6 

796-8 

796-0 

795-2 

796-0 

795-2 

794-4 

793-6 

792-8 

792-0 

792-8 

792-0 

791-2 

790-4 

789-6 

788-8 

789-7 

788-9 

788-1 

787-3 

786-5 

785-7 

786-6 

785-8 

785-0 

784-2 

783-4 

782-6 

783-5 

782-7 

781-9 

781-1 

780-3 

779-5 

780-4 

779-6 

778-8 

778-0 

777-3 

776-5 

777-3 

776-6 

775-8 

775-0 

774-2 

773-4 

774-3 

773-5 

772-8 

772-0 

771-2 

770-4 

771-3 

7705 

769-8 

769-0 

768-2 

767-4 

768-3 

767-6 

766-8 

766-0 

765-2 

764-5 

765-4 

764-6 

763-8 

763-1 

762-3 

761-5 

762-4 

761-7 

760-9 

760-1 

759-4 

758-6 

759-5 

758-8 

758-0 

757-2 

756-5 

755-7 

756-6 

755-9 

755-1 

754-4 

753-6 

752-8 

753-8 

753-0 

752-3 

751-5 

750-8 

750-0 

750-9 

750-2 

749-4 

748-7 

747-9 

747-2 

748-1 

747^4 

746-6 

745-9 

745-1 

744-4 

745-3 

744-6 

743-8 

743-1 

742-3 

741-6 

742-5 

741-8 

741-0 

740-3 

739-5 

738-8 

736«8 

739-0 

738-3 

737-5 

736-8 

736-1 

737-0 

736-3 

735-6 

734-8 

734-1 

733-3 

734-3 

733-6 

732-8 

732-1 

731-4 

730-6 

731-6 

730-9 

730-1 

729-4 

728-7 

727-9 

728-9 

728-2 

727-5 

726-7 

726-0 

725-3 

726-3 

725-5 

'  724-8 

724-1 

723-4 

722-6 

723-6 

722-9 

722-2 

721-4 

720-7 

720-0 

721-0 

720-3 

719-6 

718-8 

718-1 

717-4 

718-4 

717-7 

717-0 

716-2 

715-5 

714-8 

715-8 

715-1 

714-4 

713-7 

712-9 

712-2 

713-3 

712-5 

711-8 

711-1 

710-4 

709-7 

710-7 

710-0 

709-3 

708-6 

707-9 

707-1 

Q    Q    2 


696 


THE   ASSAY    OF    SILVER. 


SILVER 

Weight  of 
Assay  in 
Milligrs. 

0 

1 

2 

3 

4 

1405 

711-7 

711-0 

710-3 

709-6 

708-9 

1410 

709-2 

708-5 

707-8 

707-1 

706-4 

1415 

706-7 

706-0 

705-3 

704-6 

703-9 

1420 

704-2 

703-5 

702-8 

702-1 

701-4 

1425 

701-8 

701-0 

700-3 

699-6 

698-9 

1430 

699-3 

69S--6 

697-9 

697-2 

696-5 

1435 

696-9 

696-2 

695-5 

694-8 

694-1 

1440 

694-4 

693-7 

693-1 

692-4 

691-7 

1445 

692-0 

691-3 

690-7 

690-0 

689-3 

1450 

689-7 

689-0 

688-3 

687-6 

686-9 

1455 

687-3 

686-6 

685-9 

685-2 

684-5 

1460 

684-9 

684-2 

683-6 

682-9 

682-2 

1465 

682-6 

681-9 

681-2 

680-6 

679-9 

1470 

680-3 

679-6 

678-9 

678-2 

677-5 

1475 

678-0 

677-3 

676-6 

675-9 

675-2 

1480 

675-7 

675-0 

674-3 

673-6 

673-0 

1485 

673-4 

672-7 

672-0 

671-4 

670-7 

1490 

671-1 

670-5 

669-8 

669-1 

668-5 

1495 

668-9 

668-2 

667-6 

666-9 

666-2 

1500 

666-7 

666-0 

665-3 

664-7 

664-0 

1505 

664-5 

663-8 

663-1    662-5 

661-8 

1510 

662-3 

661-6 

660-9    660-3 

659-6 

1515 

660-1 

659-4 

658-7    658-1 

657-4 

1520 

657-9 

657-2 

656-6    655-9 

655-3 

1525 

655-7 

655-1 

654-4 

653-8 

653-1 

1530 

653-6  ' 

652-9 

652-3 

651-6 

651-0 

1535 

651-5 

650-8 

650-2 

649-5 

648-9 

1540 

649-4 

648-7 

648-0 

647-4 

646-7 

1545 

647-2 

646-6 

645-9 

645-3 

644-7 

1550 

645-2 

644-5 

643-9 

643-2 

642-6 

1555 

643-1 

642-4 

641-8 

641-2 

640-5 

1560 

641-0 

640-4 

639-7 

639-1 

638-5 

1565 

639-0 

638-3 

637-7 

637-1 

636-4 

1570 

636-9 

636-3 

635-7 

635-0 

634-4 

1575 

634-9 

634-3 

633-6 

633-0 

632-4 

1580 

632-9 

632-3 

631-6 

631-0 

630-4 

1585 

630-9    630-3 

629-6 

629-0 

628-4 

1590 

628-9 

628-3 

627-7 

627-0 

626-4 

1595 

627-0 

626-3 

625-7 

625-1 

624-4 

1600 

625-0 

624-4 

623-7 

623-1 

622-5 

1605 

623-1 

622-4 

621-8 

621-2 

620-6 

1610 

621-1 

620-5 

619-9 

619-2 

618-6 

1615 

619-2    618-6 

618-0 

617-3 

616-7 

THE   ASSAY   OF   SILVER. 


597 


XITRATE—  continued. 

0 

6 

7 

8 

9 

10 

708*2 

707-5 

706-8 

706-0 

705-3 

704-6 

705-7 

705-0 

704-3 

703-5 

702-8 

702-1 

703-2 

702-5 

701-8 

701-1 

700-3 

699-6 

700-7 

700-0 

699-3 

698-6 

697-9 

697-2 

698-2 

697-5 

696-8 

696-1 

695-4 

694-7 

695-8 

695-1 

694-4 

693-7 

693-0 

692-3 

693-4 

692-7 

692-0 

691-3 

690-6 

689-9 

691-0 

690-3 

689-6 

688-9 

688-2 

687-5 

688-6 

687-9 

687-2 

,686-5 

685-8 

685-1 

686-2 

685-5 

684-8 

684-1 

683-4 

682-8 

683-8 

683-2 

682-5 

681-8 

681-1 

680-4 

681-5 

680-8 

680-1 

679-4 

678-8 

678-1 

679-2 

678-5 

677-8 

677-1 

676-4 

675-8 

676-9 

676-2 

675-5 

674-8 

674-1 

673-5 

674-6 

673-9 

673-2 

672-5 

671-9 

671-2 

672-3 

671-6 

670-9 

670-3 

669-6 

668-9 

670-0 

669-4 

668-7 

668-0 

667-3  . 

666-7 

667-8 

667-1 

666-4 

665-8 

665-1 

664-4 

665-5 

664-9 

664-2 

663-5 

662-9 

662-2 

663-3 

662-7 

662-0 

661-3 

660-7 

660-0 

661-1 

660-5 

659-8 

659-1 

658-5 

657-8 

658-9 

658-3 

657-6 

656-9 

656-3 

655-6 

656-8 

656-1 

655-4 

654-8 

654-1 

653-5 

654-6 

653-9 

653-3 

652-6 

652-0 

651-3 

652-5 

651-8 

651-1 

650-5 

649-8 

649-2 

650-3 

649-7 

649-0 

648-4 

647-7 

647-1 

648-2 

647-6 

646-9 

646-2 

645-6 

644-9 

646-1 

645-4 

644-8 

644-2 

643-5 

642-9 

644-0 

643-4 

642-7 

642-1 

641-4 

640-8 

641-9 

641-3 

640-6 

640-0 

639-3 

638-7 

639-9 

639-3 

638-6 

637-9 

637-3 

636-7 

637-8 

637-2 

636-5 

635-9 

635-3 

634-6 

635-8 

635-1 

634-5 

633-9 

633-2 

632-6 

633-8 

633-1 

632-5 

631-8 

631-2 

630-6 

631-7 

631-1 

630-5 

629-8 

629-2 

628-6 

629-7 

629-1 

628-5 

627-8 

627-2 

626-6 

627-8 

627-1 

626-5 

625-9 

625-2 

624-6 

625-8 

625-2 

624-5 

623-9 

623-3 

622-6 

623-8 

623-2 

622-6 

621-9 

621-3 

620-7 

621-9 

621-2 

620-6 

620-0 

619-4 

618-7 

619-9 

619-3 

618-7 

618-1 

617-4 

616-1 

618-0 

617-4 

616-8 

616-1 

615-5 

614-9 

616-1 

615-5 

614-9 

614-2 

613-6 

613-0 

598 


THE    ASSAY   OF   SILVER. 


SILVER 

Weight  of 

Assay  in 

0 

l 

2 

3 

4 

Milligrs. 

1620 

617-3 

616-7 

616-0 

615-4 

614-8 

1625 

615-4 

614-8 

614-1 

613-5 

612-9 

1630 

613-5 

612-9 

612-3 

611-7 

611-0 

1635 

611-6 

611-0 

610-4 

609-8 

609-2 

1640 

609-8 

609-1 

608-5 

607-9 

607-3 

1645 

607-9 

607-3 

606-7 

606-1 

605-5 

1650 

606-1 

605-4 

604-8 

604-2 

603-6 

1655 

604-2 

603-6 

603-0 

602-4 

601-8 

1660 

602-4 

601-8 

601-2 

600-6 

600-0 

1665 

600-6 

600-0 

599-4 

598-8 

598-2 

1670 

598-8 

598-2 

597-6 

597-0 

596-4 

1675 

597-0 

596-4 

595-8 

595-2 

594-6 

1680 

595-2 

594*6 

5940 

593-4 

592-9 

1685 

593-5 

592-9 

592-3 

591-7 

591-1 

1690 

591-7 

591-1 

590-5 

589-9 

589-3 

1695 

590-0 

589-4 

588-8 

588-2 

587-6 

1700 

•  588-2 

587-6 

587-1 

586-5 

585-9 

1705 

586-5 

585-9 

585-3 

584-7 

584-2 

1710 

584-8 

584-2 

583-6 

583-0 

582-5 

1715 

583-1 

582-5 

581-9 

581-3 

580-8 

1720 

581-4 

580-8 

580-2 

579-6 

579-1 

1725 

579-7 

579-1 

578-5 

578-0 

577-4 

1730 

578-0 

577-5 

576-9 

576-3 

575-7 

1735 

576-4 

575-8 

575-2 

574-6 

574-1 

1740 

574-7 

574-1 

573-6 

573-0 

572-4 

1745 

573-1 

572-5 

571-9 

571-3 

570-8 

1750 

571-4 

570-9 

570-3 

569-7 

569-1 

1755 

569-8 

569-2 

568-7 

568-1 

567-5 

1760 

568-2 

567-6 

567-8 

566-5 

565-9 

1765 

566-6 

566-0 

565-4 

564-9 

564-3 

1770 

565-0 

564-4 

563-8 

563-3 

562-7 

1775 

563-4 

562-8 

562-2 

561-7 

561-1 

1780 

561-8 

561-2 

560-7 

560-1 

559-5 

1785 

560-2 

559-7 

559-1 

558-5 

558-0 

1790 

558-7 

558-1 

557-5 

557-0 

556-4 

1795 

557-1 

556-5 

556-0 

555-4 

554-9 

1800 

555-6 

555-0 

554-4 

553-9 

553-3 

1805 

554-0 

553-5 

552-9 

552-3 

551-8 

1810 

552-5 

551-9 

551-4 

550-8 

550-3 

1815 

551-0 

550-4 

549-9 

549-3 

548-8 

1820 

549-4 

548-9 

548-3 

547-8 

547-2 

1825 

547-9 

547-4 

546-8 

546-3 

545-7 

1830 

546-4 

545-9 

545-4 

544-8 

544-3 

THE   ASSAY   OF   SILVER. 


599 


NITRATE—  continued. 

5 

6 

7 

8 

9 

10 

614-2 

613-6 

613-0 

612-3 

611-7 

611-1 

612-3 

611-7 

611-1 

610-5 

609-8 

609-2 

610-4 

609-8 

609-2 

608-6 

608-0 

607-4 

608-6 

607-9 

607-3 

606-7 

606-1 

605-5 

606-7 

606-1 

605-5 

604-9 

604-3 

603-7 

604-9 

604-3 

603-6 

603-0 

602-4 

601-8 

603-0 

602-4 

601-8 

601-2 

600-6 

600-0 

601-2 

600-6 

600-0 

599-4 

598-8 

598-2 

599-4 

598-8 

598-2 

597-6 

597-0 

596-4 

597-6 

597-0 

596-4 

595-8 

595-2 

594-6 

595-8 

595-2 

594-6 

594-0 

593-4 

592-8 

594-0 

593-4 

592-8 

592-2 

591-6 

591-0 

592-3 

591-7 

591-1 

590-5 

589-9 

589-3 

590-5 

589-9 

589-3 

588-7 

588-1 

587-5 

588-8 

588-2 

587-6 

587-0 

586-4 

585-8 

587-0 

586-4 

585-8 

585-2 

584-7 

584-1 

585-3 

584-7 

584-1 

583-5 

582-9 

582-3 

583-6 

583-0 

582-4 

581-8 

581-2 

580-6 

581-9 

581-3 

580-7 

580-1 

579-5 

578-9 

580-2 

579-6 

579-0 

578-4 

577-8 

577-3 

578-5 

577-9 

577-3 

576-7 

576-2 

575-6 

576-8 

576-2 

575-6 

575-1 

574-5 

573-9 

575-1 

574-6 

574-0 

573-4 

572-8 

572-2 

573-5 

572-9 

572-3 

571-8 

571-2 

570-6 

571-8 

571-3 

570-7 

570-1 

569-5 

569-0 

570-2 

569-6 

569-0 

568-5 

567-9 

567-3 

568-6 

568-0 

567-4 

566-9 

566-3 

565-7 

566-9 

566-4 

565-8 

565-2 

564-7 

564-1 

565-3 

564-8 

564-2 

563-6 

563-1 

562-5 

563-7 

563-2 

562-6 

562-0 

561-5 

560-9 

562-1 

561-6 

561-0 

560-4 

559-9 

559-3 

560-6 

560-0 

559-4 

558-9 

558-3 

557-7 

559-0 

558-4 

557-9 

557-3 

556-7 

556-2 

557-4 

556-9 

556-3 

555-7 

555-2 

554-6 

555-9 

555-3 

554-7 

554-2 

553-6 

553-1 

554-3 

553-8 

553-2 

552-6 

552-1 

551-5 

552-8 

552-2 

551-7 

551-1 

550-6 

550-0 

551-2 

550-7 

550-1 

549-6 

549-0 

548-5 

549-7 

549-2 

548-6 

548-1 

547-5 

547-0 

548-2 

547-7 

547-1 

546-6 

546-0 

545-5 

546-7 

546-2 

545-6 

545-1 

544-5 

544-0 

545-2 

544-7 

544-1          543-6 

543-0 

542-5 

542-7 

54?-2 

542-6          542-1 

541-5 

541-0 

600 


THE   ASSAY   OF   SILVER. 


SILVEK 

Weight  of 
Assay  in 
Milligrs. 

0 

1 

2 

3 

4 

1835 

545-0 

544-4 

543-9 

543-3 

542-8 

1840 

543-5 

542-9 

542-4 

541-8 

541-3 

1845 

542-0 

541-5 

540-9 

540-4          539-8 

1850 

540-5 

540-0 

539-5 

538-9          538-4 

1855 

539-1 

538-5 

538-0 

537-5          536-9 

1860 

537-6 

537-1 

536-6 

536-0 

535-5 

1865 

536-2 

535-7 

535-1 

534-6          534-0 

1870 

534-8 

534-2 

533-7 

533-2 

532-6 

1875 

533-3 

532-8 

532-3 

531-7 

531-2 

1880 

531-9 

531-4 

530-8 

530-3          529-8 

1885 

530-5 

530-0 

529-4 

528-9 

528-4 

1890 

529-1 

528-6 

528-0 

527-5 

527-0 

1895 

527-7 

527-2 

526-6 

526-1          525-6 

1900 

526-3 

525-8 

525-3 

524-7 

524-2 

1905 

524-9 

524-4 

523-2 

523-4 

522-8 

1910 

523-6 

523-0 

522-5 

522-0 

521-5 

1915 

522-2 

521-7 

521-1 

520-6 

520-1 

1920 

520-8 

520-3 

519-8 

519-3 

518-7 

1925 

519-5 

519-0 

518-4 

517-9 

517-4 

1930 

518-1 

517-6 

517-1 

516-6 

516-1 

1935 

516-8 

516-3 

515-8 

515-2 

514-7 

1940 

515-5 

514-9 

514-4 

513-9 

513-4 

1945 

514-1 

513-6 

513-1 

512-6 

512-1 

1950 

512-8 

512-3 

511-8 

511-3 

510-8 

1955 

511-5 

511-0 

510-5 

510-0 

509-5 

1960 

510-2 

509-7 

509-2 

508-7 

508-2 

1965 

508-9 

508-4 

507-9 

507-4 

506-9 

1970 

507-6 

507-1 

506-6 

506-1 

505-7 

1975 

506-3 

505-8 

505-3 

504-8 

504-3 

1980 

505-0 

504-5 

504-0 

503-5 

503-0 

1985 

503-8 

503-3 

502-8 

502-3          501-8 

1990 

502-5 

502-0 

501-5 

501-0          500-5 

1995 

501-3 

500-7 

500-2 

499-7 

499-2 

2000 

500-0 

499-5 

499-0 

498-5 

498-0 

THE   ASSAY    OF   SILVER. 


601 


NITRATE—  cmtinued. 

5 

6 

7 

8 

9 

10 

542-2 

541-7 

541-1 

540-6 

540-0 

539-5 

540-8 

540-2 

539-7 

539-1 

538-6 

538-0 

539-3 

538-7 

538-2 

537-7 

537-1 

536-6 

537-8 

537-3 

536-8 

536-2 

535-7 

535-1 

536-4 

535-8 

535-3 

534-8 

534-2 

533-7 

534-9 

534-4 

533-9 

533-3 

532-8 

532-3 

533-5 

533-0 

532-4 

531-9 

531-4 

530-8 

532-1 

531-5 

531-0 

530-5 

529-9 

529-4 

530-7 

530-1 

529-6 

529-1 

528-5 

528-0 

529-3 

528-7 

528-2 

527-7 

527-1 

526-6 

527-8 

527-3 

526-8 

526-3 

525-7 

525-2 

526-5 

525-9 

525-4 

524-9 

524-3 

523-8 

525-1 

524-5 

524-0 

523-5 

523-0 

522-4 

* 

523-7 

523-2 

522-6 

522-1 

521-6 

521-0 

522-3 

521-8 

521-3 

520-7 

520-2 

519-7 

•  520-9 

520-4 

519-9 

519-4 

518-8 

518-3 

519-6 

519-1 

518-5 

518-0 

517-5 

517-0 

518-2 

517-7 

517-2 

516-7 

516-1 

515-6 

516-9 

516-4 

515-8 

515-3 

514-8 

514-3 

515-5 

515-0 

514-5 

514-0 

513-5          512-9 

514-2 

513-7 

513-2 

512-7 

512-1          511-6 

512-9 

512-4 

511-9 

511-3 

510-8 

510-3 

511-6 

511-0 

510-5 

510-0 

509-5 

509-0 

510-3 

509-7 

509-2 

508-7 

508-2 

507-7 

508-9 

508-4 

507-9 

507-4 

506-9 

506-4 

507-6 

507-1 

506-6 

506-1 

505-6 

505-1 

506-4 

505-8 

505-3 

504-8 

504-3 

503-8 

505-1 

504-6 

504-1 

503-5 

503-0 

502-5 

503-8 

503-3 

502-8 

502-3 

501-8 

501-3 

502-5 

509-0 

501-5 

501-0 

500-5 

500-0 

501-3 

500-8 

500-2 

499-7 

499-2 

498-7 

500-0 

499-5 

499-0 

498-5 

498-0 

497-5 

498-7 

498-2 

497-7 

497-2 

496-7 

496-2 

497-5 

497-0 

496-5 

496-0 

495-5 

495-0 

602 


THE   ASSAY   OF   SILVER. 


Tables  for  Determining  the  Standard  of  any  Silver 

approximately  containing 


COMMON 

Weight  cf 
Assay  in 
Milligrs. 

0 

1 

2 

3 

4 

1000 

1000-0 

1005 

995-0 

996-0 

997-0 

998-0 

999-0 

1010 

990-1 

991-1 

992-1 

993-1 

994-1 

1015 

985-2 

986-2 

987-2 

988-2 

989-2 

1020 

980-4 

981-4 

982-4 

983-3 

984-3 

1025 

975-6 

976-6 

977-6 

978-5 

979-5 

1030 

970-9 

971-8 

972-8 

973-8 

974-8 

1035 

966-2 

967-1 

968-1 

969-1 

970-0 

1040 

961-5 

962-5 

963-5 

964-4 

965-4 

1045 

956-9 

957-9 

958-8 

959-8 

960-8 

1050 

952-4 

953-3 

954-3 

955-2 

956-2 

1055 

947-9 

948-8 

949-8 

950-7 

951-7 

1060 

943-4 

944-3 

945-3 

946-2 

947-2 

1065 

939-0 

939-9 

940-8 

941-8 

942-7 

1070 

934-6 

935-5 

936-4 

937-4 

938-3 

1075 

930-2 

931-2 

932-1 

933-0 

933-9 

1080 

925-9 

926-8 

927-8 

928-7 

929-6 

1085 

921-7 

922-6 

923-5 

924-4 

925-3 

1090 

917-4 

918-3 

919-3 

920-2 

921-1 

1095 

913-2 

914-2 

915-1 

916-0 

917-0 

1100 

909-1 

910-0 

910-9 

911-8 

912-7 

1105 

905-0 

905-9 

906-8 

907-7 

908-6 

1110 

900-9 

901-8 

902-7 

903-6 

904-5 

1115 

896-9 

897-8 

898-6 

899-5 

900-4 

1120 

892-9 

893-7 

894-6 

895-5 

896-4 

1125 

888-9 

889-8 

890-7 

891-6 

892-4 

1130 

885-0 

885-8 

886-7 

887-6 

888-5 

1135 

881-1 

881-9 

882-8 

883-7 

884-6 

1140 

877-2 

878-1 

878-9 

879-8 

880-7 

1145 

873-4 

874-2 

875-1 

876-0 

876-9 

1150 

869-6 

870-4 

871-3 

872-2 

873-0 

1155 

865-8 

866-7 

867-5 

868-4 

869-3 

1160 

862-1 

862-9 

863-8 

864-7 

865-5 

1165 

858-4 

859-2 

860-1 

860-9 

861-8 

1170 

854-7 

855-6 

856-4 

857-3 

858-1 

1175 

851-1 

851-9 

852-8 

853-6 

854-5 

1180 

847-5 

848-3 

849-2 

850-0 

850-8 

1185 

843-9 

844-7 

845-6 

846-4 

847-3 

THE   ASSAY   OF   SILVER. 


603 


Alloy  by  employing  an  Amount  of  Alloy  always 
the  same  Amount  of  Silver. 


;ALT 

5 

6 

7 

8 

9 

10 

1000-0 

995-0 

996-0 

997-0 

998-0 

999-0 

1000-0 

990-1 

991-1 

992-1 

993-1 

994-1 

995-1 

985-3 

986-3 

987-2 

988-2 

989-2 

990-2 

980-5 

981-5 

982-4 

983-4 

984-4 

985-4 

975-7 

976-7 

977-7 

978-6 

979-6 

980-6 

971-0 

972-0    • 

972-9 

973-9 

974-9 

975-8 

966-3 

967-3 

968-3 

969-2 

970-2 

971-1 

961-7 

962-7 

963-6 

964-6 

965-5 

966-5 

957-1 

958-1 

959-0 

960-0 

960-9 

961-9 

952-6 

953-5 

954-5 

955-4 

956-4 

957-3 

948-1 

949-1 

950-0 

950-9 

951-9 

952-8 

943-7 

944-6 

945-5 

946-5 

947-4 

948-4 

939-3 

940-2 

941-1 

942-1 

943-0 

943-9 

934-9 

935-8 

936-7 

937-7 

938-6 

939-5 

930-6 

931-5 

932-4 

933-3 

934-3 

935-2 

926-3 

927-2 

928-1 

929-0 

930-0 

930-9 

922-0 

922-9 

923-8 

924-8 

925-7 

926-6 

917-8 

918-7 

919-6 

920-5 

921-5 

922-4 

913-6 

914-5 

915-4 

916-4 

917-3 

918-2 

909-5 

910-4 

911-3 

912-2 

913-1 

914-0 

905-4 

906:3 

907-2 

90&-1 

905-0 

909-9 

901-3 

902-2 

903-1 

904-0 

904-9 

905-8 

897-3 

898-2 

899-1 

900-0 

900-9 

901-8 

893-3 

894-2 

895-1 

896-0 

896-9 

897-8 

889-4 

890-3 

891-1 

892-0 

892-9 

893-8 

885-5 

886-3 

887-2 

888-1 

889-0 

889-9 

881-6 

882-5 

883-3 

884-2 

885-1 

886-0 

877-7 

878-6 

879-5 

880-3 

881-2 

882-1 

873-9 

874-8 

875-7 

876-5 

877-4 

878-3 

870-1 

871-0 

871-9 

872-7 

873-6 

874-5 

866-4 

867-2 

868-1 

869-0 

869-8 

870-7 

862-7 

863-5 

864-4 

865-2 

866-1 

866-9 

859-0 

859-8 

860-7 

861-5 

862-4 

863-2 

855-3 

856-2 

857-0 

857-9 

858-7 

859-6 

851-7 

852-5          853-4          854-2 

855-1 

855-9 

848-1 

848-9          849-8          850-6 

851-5 

852-3 

604 


THE   ASSAY   OF   SILVER. 


COMMON 

Weight  of 
Assay  in 
Milligrs. 

0 

i 

2 

3 

4 

1190 

840-3 

841-2 

842-0 

842-9 

843-7 

1195 

836-8 

837-7 

838-5 

839-3 

840-2 

1200 

833^3 

834-2 

835-0 

835-8 

836-7 

1205 

829-9 

830-7 

831-5 

832-4 

833-2 

1210 

826-4 

827-3 

828-1 

828-9 

829-7 

1215 

823-0 

823-9 

824-7 

825-5 

826-3 

1220 

819-7 

820-5 

821-3 

822-1 

822-9 

1225 

816-3 

817-1 

818-0 

818-8 

819-6 

1230 

813-0 

813-8 

814-6 

815-4 

816-3 

1235 

809-7 

810-5 

811-3 

812-1 

813-0 

1240 

806-5 

807-3 

808-1 

808-9 

809-7 

1245 

803-2 

804-0 

804-8 

805-6 

806-4 

1250 

800-0 

800-8 

801-6 

802-4 

803-2 

1255 

796-8 

797-6 

798-4 

799-2 

800-0 

1260 

793-6 

794-4 

795-2 

796-0 

796-8 

1265 

790-5 

791-3 

792-1 

792-9 

793-7 

127,0 

787-4 

788-2 

789-0 

789-8 

790-5 

1275 

784-3 

785-1 

785-9 

786-7 

787-4 

128® 

781-2 

782-0 

782-8 

783-6 

784-4 

1285. 

778-2 

779-0 

779-8 

780-5 

781-3 

1290 

775-2 

776-0 

776-7 

777-5 

778-3 

1295 

772-2 

773-0 

773-7 

774-5 

775-3 

1300 

769-2 

770-0 

770-8 

771-5 

772-3 

1305'. 

766-3 

767-0 

767-8 

768-6 

769-3 

1310 

763-4 

764-1 

764-9 

765-6 

766-4 

1315 

760-5 

761-2 

762-0 

762-7 

763-5 

13'20 

757-6 

758-3 

759-1 

759-8 

760-6 

1325 

754-7 

755-5 

756-2 

757-0 

757-7 

1330 

751-9 

752-6 

753-4 

754-1 

754-9 

1335 

749-1 

749-8 

750-6 

751-3 

752-1 

1340 

746-3 

747-0 

747-8 

748-5 

749-2 

1345 

743-5 

744-2 

745-0 

745-7 

746-5 

1350 

740-7 

741-5  . 

742-2 

743-0 

743-7 

1355 

738-0 

738-7 

739-5 

740-2 

741-0 

1360 

735-3 

736-0 

736-8 

737-5 

738-2 

1365 

732-6 

733-3 

734-1 

734-8 

735-5 

1370 

729-9 

730-7 

731-4 

732-1 

732-8 

1375 

727-3 

728-0 

728-7 

729-4 

730-2 

13.80 

724-6 

725-4 

726-1 

726-8 

727-5 

1385 

722-0 

722-7 

723-5 

724-2 

724-9 

1390 

719-4 

720-1 

720-9 

721-6 

722*3 

1395 

716-8 

717-6 

718-3 

719-0 

719-7 

1400 

714-3 

715-0 

715-7 

716-4  ' 

717-1 

THE   ASSAY    OF   SILVER, 


605 


SALT  —  continued. 

5 

6 

7 

8 

9 

10 

844-5 

845-4 

846-2 

847-1 

847-9 

848-7 

841-0 

841-8 

842-7 

843-5 

844-3 

845-2 

837-5 

838-3 

839-2 

840-0 

840-8 

841-7 

834-0 

834-8 

835-7 

836-5 

837-3 

838-2 

830-6 

831-4 

832-2 

833-1 

833-9 

834-7 

827-2 

828-0 

828-8 

829-6 

830-4 

831-3 

823-8 

824-6 

825-4 

826-2 

827-0 

827-9 

820-4 

821-2 

822-0 

822-9 

823-7 

824-5 

817-1 

817-9 

818-7 

819-5 

820-3 

821-1 

813-8 

814-6 

815-4 

816-2 

817-0 

817-8 

810-5 

811-3 

812-1 

812-9 

813-7 

814-5 

807-2 

808-0 

808-8 

809-6 

810-4 

811-2 

804-0 

804-8 

805-6 

806-4 

807-2 

808-0 

800-8 

801-6 

802-4 

803-2 

804-0 

804-8 

797-6 

798-4 

799-2 

800-0 

800-8 

801-6 

794-5 

795-3 

796-0 

796-8 

797-6 

798-4 

791-3 

792-1 

792-9 

793-7 

794-5 

795-3 

788-2 

789-0 

789-8 

790-6 

791-4 

792-2 

785-2 

786-0 

786-7 

787-5 

788-3 

789-1 

782-1 

782-9 

783-7 

784-4 

785-2 

786-0 

779-1 

779-8 

780-6 

781-4 

782-2 

782-9 

776-1 

776-8 

777-6 

778-4 

779-1 

779-9 

773-1 

773-8 

774-6 

775-4 

776-1 

776-9 

770-1 

770-9 

771-6 

772-4 

773-2 

773-9 

767-2 

767-9 

768-7 

769-5 

770-2 

771-0 

764-3 

765-0 

765-8 

766-5 

767-3 

768-1 

761-4 

762-1 

762-9 

763-6 

764-4 

765-2 

758-5 

759-2 

760-0 

760-7 

761-5 

762-3 

755-6 

756-4 

757-1 

757-9 

758-6 

759-4 

752-8 

753-6 

754-3 

755-1 

755-8 

756-6 

750-0 

750-7 

751-5 

752-2 

753-0 

753-7 

747-2 

748-0 

748-7 

749-4 

750-2 

750-9 

744-4 

745-2 

745-9 

746-7 

747-4 

748-1 

741-7 

742-4 

'743-2 

743-9 

744-6 

745-4 

739-0 

739-7 

740-4 

741-2 

741-9 

742-6 

736-3 

737-0 

737-7 

738-5 

739-2 

739-9 

733-6 

734-3 

735-0 

735-8 

736-5 

737-2 

730-9 

731-6 

732-4 

733-2 

733-8 

734-5 

728-3 

729-0 

729-7 

730-4 

731-2 

731-9 

725-6 

726-3 

727-1 

727-8 

728-5 

729-2 

723-0 

723-7 

724-5 

725-2 

725-9 

726-6 

720-4          721-1 

721-9 

722-6 

723-3 

724-0 

717-9 

718-6 

719-3          720-0 

720-7 

721-4 

606 


THE   ASSAY    OF   SILVER. 


COMMON 


Weight  of 
Assay  in 
Milligrs. 

0 

1 

2 

3 

4 

1405 

711-7 

712-5 

713-2 

713-9 

714-6 

1410 

709-2 

709-9 

710-6 

711-3 

712-1 

1415 

706-7 

707-4 

708-1 

708-8 

709-5 

1420 

704-2 

704-9 

705-6 

706-3 

707-0 

1425 

701-8 

702-5 

703-2 

703-9 

704-6 

1430 

699-3 

700-0 

700-7 

701-4 

702-1 

1435 

696-9 

697-6 

698-3 

698-9 

699-6 

1440 

694-4 

695-1 

695-8 

696-5 

697-2 

1445 

692-0 

692-7 

693-4 

694-1 

694-8 

1450 

689-7 

690-3 

691-0 

691-7 

692-4 

1455 

687-3 

688-0 

688-7 

689-3 

690-0 

1460 

684-9 

685-6 

686-3 

687-0 

687-7 

1465 

682-6 

683-3 

684-0 

684-6 

685-3 

1470 

680-3 

680-9 

681-6 

682-3 

683-0 

1475 

678-0 

678-6 

679-3 

680-0 

680-7 

1480 

675-7 

676-3 

677-0 

677-7 

678-4 

1485 

673-4 

674-1 

674-7 

675-4 

676-1 

1490 

671-1 

671-8 

672-5 

673-1 

673-8 

1495 

668-9 

669-6 

670-2 

670-9 

671-6 

1500 

666-7 

667-3 

668-0 

668-7 

669-3 

1505 

664-5 

665-1 

665-8 

666-4 

667-1 

1510 

662-3 

662-9 

663-6 

664-2 

664-9 

1515 

660-1 

660-7 

661-4 

662-0 

662-7 

1520 

657-9 

658-5 

659-2 

659-9 

660-5 

1525 

655-7 

656-4 

657-0 

657-7 

658-4 

1530 

653-6 

654-2 

654-9 

655-6 

656-2 

1535 

651-5 

652-1 

652-8 

653-4 

654-1 

1540 

649-4 

650-0 

650-6 

651-3 

651-9 

1545 

647-2 

647-9 

648-5 

649-2 

649-8 

1550 

645-2 

645-8 

646-4 

647-1 

647-7 

1555 

643-1 

643-7 

644-4 

645-0 

645-7 

1560 

641-0 

641-7 

642-3 

642-9 

643-6 

1565 

639-0 

639-6 

640-3 

640-9 

641-5 

1570 

636-9 

637-6 

638-2 

638-8 

639-5 

1575 

634-9 

635-6 

636-2 

636-8 

637-5 

1580 

632-9 

633-5 

634-2 

634-8 

635-4 

1585 

630-9 

631-5 

632-2 

632-8 

633-4 

1590 

628-9 

629-6 

630-2 

630-8 

631-4 

1595 

627-0 

627-6 

628-2 

628-8 

629-5 

1600 

625-0 

625-6 

626-2 

626-9 

627-5 

1605 

623-1 

623-7 

624-3 

624-9 

625-5 

1610 

621-1 

621-7 

622-4 

623-0 

623-6 

1615 

619-2 

619-8 

620-4 

621-0 

621-7 

THE   ASSAY   OF   SILVER. 


607 


SALT—  continued. 

5 

6 

7 

8 

9 

10 

715-3 

716-0 

716-7 

717-4 

718-1 

718-9 

712-8 

713-5 

714-2 

714-9 

715-6 

716-3 

710-2 

710-9 

711-7 

712-4 

713-1 

713-8 

707-7 

708-4 

709-2 

709-9 

710-6 

711-3 

705-3 

706-0 

706-7 

707-4 

708-1 

708-8 

702-8 

703-5 

704-2 

704-9 

705-6 

706-3 

700-3 

701-0 

701-7 

702-4 

703-1 

703-8 

697-9 

698-6 

699-3 

700-0 

700-7 

701-4 

695-5 

696-2 

696-9 

697-6 

698-3 

699-0 

693-1 

693-8 

694-5 

695-2 

695-9 

696-6 

690-7 

691-4 

692-1 

692-8 

693-5 

694-2 

688-4 

689-0 

689-7 

690-4 

691-1 

691-8 

686-0 

686-7 

687-4 

688-0 

688-7 

689-4 

683-7 

684-3 

685-0 

685-7 

686-4 

687-1 

681-4 

682-0 

682-7 

683-4 

684-1 

684-7 

679-1 

679-7 

680-4 

681-1 

681-8 

682-4 

676-8 

677*4 

678-1 

678-8 

679-5 

680-1 

674-5 

675-2 

675-8 

676-5 

677-2 

677-8 

672-2 

672-9 

673-6 

674-2 

674-9 

675-6 

670-0 

670-7 

671-3 

672-0 

672-7 

673-3 

667-8 

668-4 

669-1 

669-8 

670-4 

671-1 

665-6 

666-2 

666-9 

667-5 

668-2 

668-7 

663-4 

664-0 

664-7 

665-3 

666-0 

656-7 

661-2 

661-8 

662-5 

663-2 

663-8 

664-5 

659-0 

659-7 

660-3 

661-0 

661-6 

662-3 

656-9 

657-5 

658-2 

658-8 

659-5 

660-1 

654-7 

655-4 

656-0 

656-7 

657-3 

658-0 

652-6 

653-2 

653-9 

654-5 

655-2 

655-8 

650-5 

651-1 

651-8 

652-4 

653-1 

653-7 

648-4 

649-0 

649-7 

650-3 

651-0 

651-6 

646-3 

646-9 

647-6 

648-2 

648-9 

649-5 

644-2 

644-9 

645-5 

646-1 

646-8 

647-4 

642-2 

642-8 

643-4 

644-1 

644-7 

645-4 

640-1 

640-8 

641-4 

642-0 

642-7 

643-3 

638-1 

638-7 

639-4 

640-0 

640-6 

641-3 

636-1 

636-7 

637-3 

638-0 

638-6 

639-2 

634-1 

634-7 

635-3 

636-0 

636-6 

.    637-2 

632-1 

632-7 

633-3 

634-0 

634-6 

635-2 

630-1 

630-7 

631-3 

632-0 

632-6 

633-2 

628-1 

628-7 

629-4 

030-0 

630-6 

631-2 

626-2 

626-8 

627-4 

628-0 

628-7 

629-3 

624-2 

624-8 

625-5 

626-1 

626-7 

627-3 

622-3 

622-9 

623  5 

624-1 

624-8 

625-4 

008 


THE   ASSAY   OF   SILVEE. 


COMMON 

Weight  of 
Assay  in 

Milligrs. 

0 

i 

2 

3 

4 

1620 

617-3 

617-9 

618-5 

619-1 

619-7 

1625 

615-4 

616-0 

616-6 

617-2 

617-8 

1630 

613-5 

614-1 

614-7 

615-3 

615-9 

1635 

611-6 

612-2 

612-8 

613-5 

614-1 

1640 

609-8 

610-4 

611-0 

611-6 

612-2 

1645 

607-9 

608-5 

609-1 

609-7 

610-3 

1650 

606-1 

606-7 

607-3 

607-9 

608-5 

1655 

604-2 

604-8 

605-4 

606-0 

606-6 

1660 

602-4 

603-0 

603-6 

604-2 

604-8 

1665 

600-6 

601-2 

601-8 

602-4 

603-0 

1670 

598-8 

599-4 

600-0 

600-6 

601-2 

1675 

597-0 

597-6 

598-2 

598-8 

599-4 

1680 

595-2 

595-8 

596-4 

597-0 

597-6 

1685 

593-5 

594-1 

594-7 

595-2 

595-8 

1690 

591-7 

592-3 

592-9 

593-5 

594-1 

1695 

590-0 

590-6 

591-1 

591-7 

592-3 

1700 

588-2 

588-8 

589-4 

590-0 

590-6 

1705 

586-5 

587-1 

587-7 

588-3 

588-9 

1710 

584-8 

585-4 

586-0 

586-5 

587-1 

1715 

583-1 

583-7 

584-3 

584-8 

585-4 

1720 

581-4 

582-0 

582-6 

583-1 

583-7' 

1725 

579-7 

580-3 

580-9 

581-4 

582-0 

1730 

578-0 

578-6 

579-2 

579-8 

580-3 

1735 

576-4 

576-9 

577-5 

578-1 

578-7 

1740 

574-7 

575-3 

575-9 

576-4 

577-0 

]745 

573-1 

573-6 

574-2 

574-8 

575-4 

1750 

571-4 

572-0 

572-6 

573-1 

573-7 

1755  ' 

569-8 

570-4 

570-9 

571-5 

572-1 

1760 

568-2 

568-7 

569-3 

569-9 

570-4 

1765 

566-6 

567-1 

567-7 

568-3 

568-8 

1770 

565-0 

565-5 

566-1 

566-7 

567-2 

1775 

563-4 

563-9 

564-5 

565-1 

565-6 

1780 

561-8 

562-4 

562-9 

563-5 

564-0 

1785 

560-2 

560-8 

561-3 

561-9 

562-5 

1790 

558-7 

559-2 

559-8 

560-3 

560-9 

1795 

557-1 

557-7 

558-2 

558-8 

559-3 

1800 

555-6 

556-1 

556-7 

557-2 

557-8 

1805 

554-0 

554-6 

555-1 

555-7 

556-2 

1810 

552-5 

553-0 

553-6 

554-1 

554-7 

1815 

551-0 

551-5 

552-1 

552-6 

553-2 

1820 

549-4 

550-0 

550-5 

551-1 

551-6 

1825 

547-9 

548-5 

549-0 

549-6 

550-1 

1830 

546-4 

547-0 

547-5 

548-1 

548-6 

THE   ASSAY   OF   SILVER. 


SALT— continued. 


5 

6 

7 

8 

9 

10 

620-4 

621-0 

621-6 

622-2 

622-8 

623-5 

618-5 

619-1 

619-7 

620-3 

620-9 

621-5 

616-6 

617-2 

617-8 

618-4 

619-0 

619-6 

614-7 

615-3 

615-9 

616-5 

617-1 

617-7 

612-8 

613-4 

614-0 

614-6 

615-2 

615-8 

610-9 

611-5 

612-2 

612-8 

613-4 

614-0 

609-1 

609-7 

610-3 

610-9 

611-5 

612-1 

607-2 

607-8 

608-5 

609-1 

609-7 

610-3 

605-4 

606-0 

606-6 

607-2 

607-8 

608-4 

603-6 

604-2 

604-8 

605-4 

606-0 

606-6 

601-8 

602-4 

603-0 

603-6 

604-2 

604-8 

600-0 

600-6 

601-2 

601-8 

602-4 

603-0 

598-2 

598-8 

599-4 

600-0 

600-6 

601-2 

596-4 

597-0 

597-6 

598-2 

598-9 

599-4 

594-7 

595-3 

595-9 

596-4 

597-0 

597-6 

592-9 

593-5 

594-1 

594-7 

595-3 

595-9 

591*2 

591-8 

592-3 

592-9 

593-5 

594-1 

589-4 

590-0 

590-6 

591-2 

591-8 

592-4 

587-7 

588-3 

588-9 

589-5 

590-1 

590-6 

586-0 

586-6 

587-2 

587-8 

588-3 

588-9 

584-3 

584-9 

585-5 

586-0 

586-6 

587-2 

582-6 

583-2 

583-8 

584-3 

584-9 

585-5 

580-9 

581-5 

582-1 

582-7 

583-2 

583-8 

579-2 

579-8 

580-4 

581-0 

581-6 

582-1 

577-6 

578-2 

578-7 

579-3 

579-9 

580-5 

575-9 

576-5 

577-1 

577-6 

578-2 

578-8 

574-3 

574-9 

575-4 

576-0 

576-6 

577-1 

572-6 

573-2 

573-8 

574-4 

574-9 

575-5 

571-0 

571-6 

572-2 

572-7 

573-3 

573-9 

569-4 

570-0 

570-5 

571-1 

571-7 

572-2 

567-8 

568-4 

568-9 

569-5 

570-1 

570-6 

566-2 

566-8 

567-3 

567-9 

568-4 

569-0 

564-6 

565-2 

565-7 

566-3 

566-8 

567-4 

563-0 

563-6 

564-1 

564-7 

565-3 

565-8 

561-4 

562-0 

562-6 

563-1 

563-7 

564-2 

559-9 

560-4 

561-0 

561-6 

562-1 

562-7 

558-3 

558-9 

559-4 

560-0 

560-6 

561-1 

556-8 

557-3 

557-9 

558-4 

559-0 

559-6 

555-2 

555-8 

556-3 

556-9 

557-5 

558-0 

553-7 

554-3 

554-8 

555-4 

555-9 

556-5 

552-2 

552-7 

553-3 

553-8 

554-4 

554-9 

550-7 

551-2 

551-8 

552-3 

552-9 

553-4 

549-2 

549-7 

550-3 

550-8 

551-4 

551-9 

R, 


610 


THE   ASSAY   OF   SILVER. 


COMMON 

Weight  of 

Assay  in 

0 

l 

2 

3 

4 

Milligrs. 

1835 

545-0 

545-5 

546-0 

546-6 

547-1 

1840 

543-5 

544-0 

544-6 

545-1 

545-6 

1845 

542-0 

542-5 

543-1 

543-6 

544-2 

1850 

540-5 

541-1 

541-6 

542-2 

542-7 

1855 

539-1 

539-6 

540-2 

540-7 

541-2 

1860 

537-6 

538-2 

538-7 

539-2 

539-8 

1865 

536-2 

536-7 

537-3 

537-8 

538-3 

1870 

534-8 

535-3 

535-8 

536-4 

536-9 

'  1875 

533-3 

533-9 

534-4 

534-9 

535-5 

1880 

531-9 

532-4 

533-0 

533-5 

534-0 

1885 

530-5 

531-0 

531-6 

532-1 

532-6 

1890 

529-1 

529-6 

530-2 

530-7 

531-2 

1895 

527-7 

528-2 

528-8 

529-3 

529-8 

1900 

526-3 

526-8 

527-4 

527-9 

528-4 

1905 

524-9 

525-4 

526-0 

526-5 

527-0 

1910 

523-6 

524-1 

524-6 

525-1 

525-6 

1915 

522-2 

522-7 

523-2 

523-8 

524-3 

1920 

520-8 

521-3 

521-9 

522-4 

522-9 

1925 

519-5 

520-0 

520-5 

521-0 

521-6 

1930 

518-1 

518-6 

519-2 

519-7 

520-2 

1935 

516-8 

517-3 

517-8 

518-3 

518-9 

1940 

515-5 

516-0 

516-5 

517-0 

517-5 

1945 

514-1 

514-6 

515-2 

515-7 

516-2 

1950 

512-8 

513-3 

513-8 

514-4 

514-9 

1955 

511-5 

512-0 

512-5 

513-0 

513-5 

1960 

510-2 

510-7 

511-2 

511-7 

512-2 

1965 

508-9 

509-4 

509-9 

510-4 

510-9 

1970 

507-6 

508-1 

508-6 

509-1 

509-6 

1975 

506-3 

506-8 

507-3 

507-8 

508-3 

1980 

505-0 

505-6 

506-1 

506-6 

507-1 

1985 

503-8 

504-3 

504-8 

505-3 

505-8 

1990 

502-5 

503-0 

503-5 

504-0 

504-5 

1995 

501-3 

501-8 

502-3 

502-8 

503-3 

2000 

500-0 

500-5 

501-0 

501-5 

502-0 

THE   ASSAY   OF   SILVER. 


611 


SALT—  continued. 

5 

6 

7 

8 

9 

10 

547-7 

548-2 

548-8 

549-3 

549-9 

550-4 

546-2 

546-7 

547-3 

547-8 

548-4 

548-9 

544-7 

545-3 

545-8 

546-3 

546-9 

547-4 

543-2 

543-8 

544-3 

544-9 

545-4 

545-9 

541-8 

542-3 

542-9 

543-4 

543-9 

544-5 

540-3 

540-9 

541-4 

541-9 

542-5 

543-0 

538-9 

539-4 

539-9 

540-5 

541-0 

541-5 

537-4 

538-0 

538-5 

539-0 

539-6 

540-1 

536-0 

536-5 

537-1 

537-6 

538-1 

538-7 

534-6 

535-1 

535-6 

536-2 

536-7 

537-2 

533-2 

533-7 

534-2 

534-7 

535-3 

535-8 

531-7 

532-3 

532-8 

533-3 

533-9 

534-4 

530-3 

530-9 

531-4 

531-9 

532-4 

533-0 

528-9 

529-5 

530-0 

530-5 

531-0 

531-6 

527-6 

528-1 

5^8-6 

529-1 

529-7 

530-2 

526-2 

526-7 

527-2 

527-7 

528-3 

528-8 

524-8- 

525-3 

525-8 

526-4 

526-9 

527-4 

523-4 

524-0 

524-5 

525-0 

525-5 

526-0 

522-1 

522-6 

523-1 

523-6 

524-2 

524-7 

520-7 

521-2 

521-8 

522-3 

522-8 

523-3 

519-4 

519-9 

520-4 

5209 

521-4 

522-0 

518-0 

518-6 

519-1 

519-6 

520-1 

520-6 

516-7 

517-2 

517-7 

518-2 

518-8 

519-3 

515-4 

515-9 

516-4 

516-9 

517-4 

517-9 

514-1 

514-6 

515-1 

515-6 

516-1 

516-6 

512-8 

513-3 

513-8 

514-3 

514-8 

515-3 

511-4 

512-0 

512-5 

513-0 

513-5 

514-0 

510-1 

510-7 

511-2 

511-7 

512-2 

512-7 

508>9 

509-4 

509-9 

510-4 

510-9 

511-4 

507-6 

508-1 

508-6 

509-1 

509-6 

510-1 

506-3 

506-8 

507-3 

507-8 

508-3 

508-8 

505-0 

505-5 

506-0 

506-5 

507-0 

507-5 

503-8 

504-3 

504-8 

505-3 

505-8 

506-3 

502-5 

503-0 

503-5 

504-0 

504-5 

505-0 

R    R  2 


THE   ASSAY   OF   SILVER. 


APPLICATION. 

Assay  of  Pure,  or  nearly  Pure,  Silver,  the  Temperature  of 
the  Normal  Solution  of  Salt  being  that  at  which  it  was 
standardised. 

First  Example. — Let  the  ingot  of  silver  have  an  ap- 
proximative standard  of  from  995  to  1000  thousandths. 
Take  one  gramme ;  dissolve  it  in  ten  grammes  of  nitric 
acid,  in  the  bottle,  fig.  106.  Then  pour  into  the  bottle  an 
exact  measure  of  the  normal  solution  of  salt,  and  brighten 
by  agitation.  The  silver  not  being  supposed  to  be  quite 
pure,  the  standard  is  not  further  sought  for  by  the  decime 
solution  of  salt,  but  that  of  silver  nitrate  is  employed. 

One  thousandth  of  this  latter  solution  is  poured  into 
the  bottle;  it  becomes  cloudy,  and  is  well  agitated.  A 
second  and  a  third  thousandth  also  give  a  precipitate,  but 
not  so  a  fourth.  From  these  data  the  following  is  the 
method  of  ascertaining  the  standard  of  the  alloy  : — 

The  last  thousandth  of  the  decime  solution  of  silver, 
having  produced  no  cloudiness,  is  not  to  be  counted.  The 
third  was  necessary,  but  only  partially  so ;  consequently 
the  number  of  thousandths  of  silver  necessary  to  decom- 
pose the  excess  of  salt  is  more  than  2  and  less  than  3  ;  in 
other  words,  it  is  equal  to  the  mean,  2^ ;  bujt  since  2^ 
thousandths  of  silver  have  been  required  to  complete  the 
precipitation  of  salt  representing  1000  thousandths  of 
silver,  it  is  evident  that  the  silver  submitted  to  ^ssay  con- 
tained 2^  thousandths  of  alloy,  and  that  its  standard,  to 
within  nearly  half  a!  thousandth,  is  but  997^. 

If  it  be  considered  necessary  to  arrive  nearer  the  true 
standard,  the  following  proofs  must  be  employed  : — Pour 
into  the  solution  1^  thousandths  of  salt,  which  will  decom- 
pose a  like  number  of  thousandths  of  silver.*  After  due 

*  It  has  already  been  stated  how  a  thousandth  of  the  decime  solution  may 
"be  subdivided  "by  the  number  of  drops  furnished  by  the  pipette.  If,  for  in- 
stance, it  contains  20  drops,  10  will  give  the  half,  5  the  quarter,  &c.  Half  a 
thousandth  may  also  be  obtained  by  diluting  the  solution  with  its  volume  of 
water,  and  using  a  whole  pipetteful.  This  latter  plan  has  been  found  the  best 
in  practice. 


ASSAY   OF   PURE,    OR   NEARLY   PURE,    SILVER.  613 

agitation,  add  half  a  thousandth  of  silver  nitrate.  Sup- 
posing a  cloudiness  is  produced,  no  further  addition  must 
be  made  ;  for  it  is  already  known  that  above  the  third 
thousandth  no  precipitate  is  formed  in  the  liquid  by  silver 
nitrate,  and  consequently  only  half  of  the  last  half-thou- 
sandth must  be  calculated,  as  only  a  portion  of  it  was 
necessary.  From  which,  the  entire  number  of  thousandths 
of  silver  nitrate  being  4|,  and  those  of  salt  1^,  there 
remains  2£  for  the  number  of  thousandths  of  nitrate  of 
silver  added  to  the  normal  solution  ;  and  consequently  the 
standard  of  the  alloy  is  1000— 2f= 997^.  If,  on  the  other 
hand,  the  last  half-thousandth  of  the  silver  nitrate  had 
produced  no  cloudiness,  it  would  not  have  to  be  reckoned, 
and  only  half  of  the  preceding  half-thousandth  would  have 
been  taken.  Thus  from  the  4  thousandths  of  silver 
nitrate  employed  a  quarter  of  a  thousandth  is  deducted ; 
and  from  the  difference,  3|,  is  yet  deducted  1^  of  salt,  the 
final  remainder  being  2i  thousandths  of  silver  nitrate  which 
have  been  added  to  the  normal  solution  :  the  standard  of 
the  alloy  would  be  1000-2i=997f. 

Although  the  above-described  operation  is  very  simple, 
yet  it  is  desirable,  in  order  to  avoid  all  confusion,  to  note 
in  writing  such  thousandths  of  salt  or  silver  nitrate  as  are 
added.  The  thousandths  of  salt  indicating  an  increase  of 
standard  should  be  preceded  by  the  sign  + ;  and  the  thou- 
sandths of  silver  nitrate  announcing  a  diminution  of  stan- 
dard, by  the  sign  — . 

Second  Example. — Suppose  the  ingot  has  a  presumed 
standard  of  895  thousandths,  and  the  temperature  of  the 
normal  solution  supposed  invariable. 

Find  in  the  table  of  standards  (Salt  Table),  first  column, 
that  which  approaches  the  nearest  to  895  ;  it  will  be 
found  to  be  896*9,  corresponding  to  the  weight*  of  1115 
milligrammes.  This  weight  of  the  alloy  is  taken  and 
dissolved  in  nitric  acid,  a  measure  of  normal  solution  of 
salt  added,  and  the  whole  well  agitated.  The  operator  is, 
however,  doubtful  whether  the  assay  must  be  proceeded 
with  by  the  decime  salt  solution,  or  the  silver  nitrate 
decime  solution.  If  .the  former  produces  a  precipitate, 


614  THE    ASSAY    OF   SILVER. 

it  is  gone  on  with  ;  but  if  it  does  not  precipitate,  that 
already  added  is  decomposed  by  a  similar  addition  of  the 
second,  and  the  solution  rendered  bright  by  agitation.  A 
starting  point  has  now  been  arrived  at  for  the  continuance 
of  the  assay,  for  it  is  known  that  the  silver  nitrate  solution 
must  be  employed. 

Suppose,  then,  that  the  alloy,  after  the  addition  of  the 
measure  of  normal  solution,  yet  gives  a  precipitate  with 
the  decime  solution  of  salt.  The  first  5  thousandths 
produce  a  precipitate,  but  not  the  sixth,  which  conse- 
quently is  not  counted.  The  fifth  has  only  been  partially 
required,  so  that  it  is  more  than  4  thousandths,  and  less 
than  5,  or  the  mean,  4|,  is  the  quantity  required  to 
entirely  precipitate  the  excess  of  silver  in  the  alloy  sub- 
mitted to  assay.  But  by  neglecting  at  first  the  fraction 
0*5,  seek  in  the  Salt  Table  of  Standards  the  number  found 
on  the  longitudinal  line  of  the  weight  1115,  under  column 
4  ;  it  is  900-4,  and  on  adding  0'5  to  this  number,  we  have 
900*9,  or  901,  for  the  required  standard. 

Supposing,  however,  that  the  same  alloy,  after  the 
addition  of  the  normal  measure  of  salt,  gives  a  precipitate 
with  silver  nitrate,  and  that  the  3  first  thousandths  pro- 
duce a  cloudiness,  but  not  the  fourth.  The  number  of 
thousandths  of  silver  nitrate  really  necessary  for  complete 
precipitation  will  be  very  nearly  2^.  To  ascertain  the 
real  standard  of  the  alloy  of  which  1115  thousandths  were 
supposed  to  contain  about  1000  thousandths  of  silver,  take 
the  number  found  in  the  horizontal  line  1115,  and  in  the 
column  2  of  the  Silver  Nitrate  Table.  This  number,  which 
is  895*1,  diminished  by  the  fraction  0'5,  gives  894*6  for 
the  standard  of  the  alloy  to  within  half  a  thousandth. 

Third  Example. — The  actual  temperature  of  the  normal 
solution  of  salt  being  18°  when  it  was  standardised  at  15°. 

The  ingot  of  silver  submitted  to  assay  has  an  approxi- 
mative standard  of  795  thousandths.  Find  in  the  Salt 
Table  of  Standards,  first  column,  that  which  is  nearest 
to  it ;  it  is  793*7,  corresponding  to  the  weight  1260. 
This  weight  of  the  alloy  is  taken,  and  the  operation  pro- 
ceeded with  as  already  described.  Supposing  it  had 


GRADUATION   OF   THE   NORMAL   SOLUTION   OP   SALT.        615 

required  6*5  thousandths  of  salt  to  precipitate  the  whole 
of  the  silver  contained  in  the  alloy  to  within  half  a 
thousandth,  the  required  standard,  without  correction 
for  temperature,  will  be  798-4  +  0-4=798-8.  But,  making 
this  correction,  recourse  must  be  had  to  the  table,  page 
589,  column  15  :  the  number  0-3,  which  will  be  found  in 
the  horizontal  line  18  and  the  column  15,  possesses  the  - 
sign ;  consequently  it  must  be  deducted  from  798*8,  and 
the  remainder,  798-5,  will  be  the  standard  weight.  If  the 
temperature  of  the  solution,  instead  of  being  3°  higher  than 
at  the  time  it  was  standardised,,  was  3°  lower,  or  12°,  the 
correction  must  be  added,  and  would  be  equal  to  +  0-2. 
The  standard  of  the  alloy  would  conse-  FlG<  112. 
quently  be  798-8  +  0-2  =  799. 

Graduation  of  the  Normal  Solution  of  Salt, 
the  Temperature  being  different  to  that  at 
which  it  was  wished  to  be  graduated. 

Two  equally  ready  processes  can  be 
employed.  The  one  consists  in  reducing 
the  temperature  of  the  solution  to  the 
desired  degree  before  standardising  ;  the 
other,  in  determining  its  standard  without 
regard  to  the  temperature  of  the  solution, 
and  then  correcting  its  influence  by  the 
aid  of  the  tables  of  correction  already 
given. 

First  Process. — Place  the  liquid  to  be 
graduated  in  a  bottle,  F,  fig.  112.  Intro- 
duce a  thermometer,  and  heat  to  a  deter- 
minate degree,  say  20°  for  instance.  This 
done,  place  the  jet  of  the  pipette  in  the 
bottle  ;  raise  the  liquid  by  aspiration  by 
means  of  the  conical  tube,  T,  fig.  112, 
which  is  adapted  to  the  opening  of  the 
air-cock,  E.  As  soon  as  the  liquid  is 
raised  a  little  above  the  mark  a  b,  which  determines  the 
capacity  of  the  pipette,  close  the  stopcock,  and  complete 


616  THE    ASSAY   OF    SILVER. 

the  measurement  as  usual.  This  same  means  of  filling 
the  pipette  by  aspiration  may  be  employed  to  fill  it  either 
with  caustic  alkali  or  nitric  acid,  as  the  case  may  be,  to 
cleanse  it  instead  of  taking  it  to  pieces. 

Second  Method. — The  solution  of  salt  being  supposed 
at  a  temperature  of  16°,  and  it  is  desired  to  graduate  it  at 
that  of  20°.  Proceed  with  the  standardising  without 
regard  to  temperature ;  but  when  it  is  obtained  in  each 
trial  assay,  it  is  necessary  to  make  the  correction  required 
by  the  temperature. 

If,  for  example,  in  an  approximative  assay  the  standard 
of  the  solution  was  expressed  by  1001*5  this  standard 
would  not  only  be  too  weak  by  1*5  thousandth,  but, 
according  to  the  table  of  temperatures,  by  yet  another 
0-5,  for  the  solution  is  weakened  by  this  quantity,  by 
passing  from  16°  to  20°.  The  standard,  if  taken  at  this 
last  temperature,  would  be  too  low  by  2  thousandths,  and 
must  consequently  be  corrected. 

If,  on  the  other  hand,  the  standard  of  the  solution  were 
too  high  instead  of  too  low,  and  expressed  by  998 -5  at  the 
temperature  of  16° ;  at  that  of  20°,  the  solution  being 
weakened  by  0'5,  the  standard  would  only  be  but  one 
thousandth  too  high,  and  it  must  be  corrected  by  that 
quantity. 

Approximative  Determination  of  the  Standard  of  an 
Unknown  Alloy. 

It  has  always  been  supposed  in  the  experiments  already 
detailed,  that  the  approximative  standard  of  the  alloy  sub- 
mitted to  assay  was  known  :  and  this,  indeed,  is  nearly 
always  the  case.  If,  however,  this  be  unknown,  two 
means  are  available  for  obtaining  the  necessary  know- 
ledge. A  decigramme  of  the  alloy  is  cupelled  with  one 
gramme  of  lead  ;  or  if  it  be  desirable  not  to  use  the  cupel, 
it  may  be  ascertained  by  the  wet  method,  in  the  follow- 
ing manner  : — 

The  assayer  supposes  the  standard  of  the  alloy  known 
to  be  about  a  twentieth,  and  it  can  always  be  found  nearer 
than  that  by  touch,  density,  &c.  A  weight  relative  to  its 


MODES   OF   ABRIDGING    MANIPULATION.  617 

supposed  standard  is  taken,  and  its  standard  sought  by 
adding  the  decime  liquid  by  10  thousandths  at  a  time, 
by  means  of  pipettes  of  this  capacity  (see  fig.     FlG  131 
113).     The  term  of  complete  precipitation   is 
soon  passed,  and  the  standard  of  the  alloy  to 
about  5  thousandths  is  thus  ascertained.     The 
approximate  standard  to  2^  thousandths  may 
be  obtained  by  adding  only  5  thousandths  of 
solution  at  a  time. 

Suppose  the  alloy  840  thousandths.  Take 
the  weight  1190,  corresponding  to  this  standard, 
and  proceed  as  in  an  ordinary  assay,  adding 
-each  time,  for  example,  a  pipette  of  10  thou- 
sandths of  salt  solution.  It  is  found  the  fifth 
pipette  gives  no  precipitate,  and  consequently 
the  number  of  thousandths  of  salt  for  the  pre- 
cipitate of  the  silver  to  within  5  thousandths  is 
35.  The  1199  of  alloy  will  therefore  contain 
1000  +  35  =  1035  of  silver  ;  and  the  approxi- 
mative standard  will  be  obtained  by  the  pro- 
portion— 

1120  :  1035  ::  1000  :  #=869-7. 

Modes  of  Abridging  Manipulation. 

In  the  statement  already  given  of  the  mode  of  con- 
ducting the  assay  by  the  wet  method,  only  such  instructions 
have  been  given  as  were  necessary  for  its  full  comprehen- 
sion, and  everything  that  might  call  away  or      FIG.  114. 
fatigue  the  attention  has  been  omitted.    Never- 
theless, here  it  will  be  convenient  to  describe 
some  methods  of  abridging  the  necessary  mani- 
pulations, supposing  that  ten,  or  at  least  five, 
assays  are  made  at  once. 

Bottles. — It  is  necessary  to  have  these  all, 
as  nearly  as  possible,  of  the  same  height  and 
diameter.  They  are  marked  progressively  on  the  shoulder, 
as  are  also  their  stoppers  (fig.  114),  thus — 1,  2,  3,  4,  &c. 
They  are  taken  successively  by  tens,  in  the  natural  order. 


618 


TfiE    ASSAY    OF    SILVEK. 


The  stoppers  are  placed  on  a  support,  numbered  in  the  same 
manner  (fig.  115).  The  support  is  pierced  with  ten  holes, 
us.  distinguished  in  precedence  by 

a  mark  between  the  fifth  and 

sixth. 

Stand.  —  Each    ten   flasks 

are  in  turn  placed  in  a  case  or 
stand  of  japanned  tin-plate  (fig.  116),  having  ten  compart- 
ments numbered  from  1  to  10.  Each  of  these  compart- 
ments is  cut  anteriorly  to  about  half  their  length,  so  as  to 


FIG.  116. 


FIG.  117. 


FIG.  118. 


allow  the  numbers  of  the  bottles  to  be  seen.  The  same 
stand  serves  for  all  the  series,  by  making  the  same  units 
correspond  :  thus,  No.  23  of  the  third  series  is  placed  in 

stand  No.  3,  &c.  When  each 
flask  is  charged  with  the 
alloy,  about  10  grammes  of 
nitric  acid,  40°  C.,  are  mea- 
sured by  a  pipette  (fig.  113) 
introduced  into  the  bottles  by 
means  of  a  funnel  with  a  large 
neck  (fig.  117).  The  whole 
are  then  exposed  to  the  heat 
of  a  water-bath,  to  facilitate 
the  solution  of  the  alloy. 

Water-bath. — This   is   an 
oblong   tin-plate   vessel,  cal- 
bottles    (fig.    118).      It   has  a 


culated    to    receive    10 


movable  double  bottom,  pierced   with   small   holes,  the 


MODES    OF   ABRIDGING   MANIPULATION.  619 

principal  object  of  which  is  to  prevent  the  fracture  of  the 
bottles  by  isolating  them  from  the  bottom  of  the  vessel, 
which  is  immediately  exposed  to  the  heat.  On  the 
movable  bottom  are  soldered  the  cylinders  c  c,  three  or 
four  centimetres  in  height,  and  above  which,  at  the  distance 
of  eight  centimetres,  is  a  sheet  of  tin  plate,  pp,  pierced  with 
ten  holes,  corresponding  to  the  cylinders,  and  connected 
with  the  movable  bottom  by  the  supports,  s  s.  These 
cylinders,  and  the  sheet  of  tin  plate,  are  destined  to  isolate 
the  bottles,  F  F,  one  from  the  other  in  the  bath,  and  to 
keep  them  some  time  suspended  over  it,  when  the  water  is 
boiling,  before  complete  immersion.  The  water-bath  may 
be  replaced  by  a  steam-bath  ;  the  bottles  will  then  be  sup- 
ported by  a  grating  above  the  surface  of  the  water.  The  so- 
lution of  the  alloy  in  the  nitric  acid  takes  place  rapidly,  and 
as  it  gives  rise  to  an  abundant  evolution  of  nitrous  vapour, 
it  must  be  made  under  a  flue  having  a  good  draught. 

Flue. — This  is  represented  at  fig.  119.  C  C  is  a  flue 
resting  on  a  table  or  support,  T  T,  about  90  centimetres 
high.  The  anterior  side  in  the  FlG  H9 

figure  is  removed  to  show  the 
water-bath  j5,  and  the  furnace 
F.  The  opening  0  of  the  flue 
is  closed  by  the  wooden  door,  p, 
movable  on  two  eccentric  pivots, 
which  keep  it  up  during  the 
solution,  and  allow  it  to  fall  so 
that  the  flask  may  be  placed 
upon  it.  The  nitrous  vapour  is 
removed  from  the  bottles  with  the  blower  (fig.  111).  The 
hood,  H,  prevents  the  diffusion  of  the  nitrous  vapour  in 
the  laboratory. 

Agitator. — Figure  120  gives  a  sufficiently  exact  idea  of 
this  apparatus,  and  dispenses  with  a  long  description.  It 
has  ten  cylindrical  compartments,  numbering  from  1  to  10. 
The  bottles,  after  solution  of  the  alloy,  are  placed  in  it  in 
the  order  of  their  numbers.  The  agitator  is  then  placed 
by  the  side  of  the  pipette,  by  which  is  measured  the  normal 
solution  of  salt,  and  into  each  flask  is  poured  a  pipetteful 


<520 


THE    ASSAY    OF    SILVER. 


of  the  solution.  The  bottles  are  fitted  with  their  stoppers, 
previously  moistened  with  distilled  water  (fig.  121) ;  they 
are  then  fixed  in  order  with  wooden  wedges  (fig.  122). 
The  agitator  is  suspended  to  a  spring,  72,  and  a  rapid 
alternating  movement  given  to  it  with  both  hands,  by  which 
the  solution  is  agitated,  and  in  less  than  a  minute  rendered 

FIG.  120. 


FIG.  121. 


FIG.   122. 


as  clear  as  water.  The  movement  is  assisted  by  a  spiral 
spring,  7?,  fixed  to  the  agitator  and  its  stand.  The  agitation 
finished,  the  wedges  are  removed,  and  placed  in  the  vacant 
spaces  between  the  compartments.  The  agitator  is  taken 
from  the  spring,  and  the  bottles  placed  in  order  on  a  table 
prepared  to  receive  them. 

Table.— This  table  (fig.  123)  has  a  double  bottom  ;  the 
upper  is  pierced  with  ten  holes,  a  little  larger  than  the 


MODES   OF   ABRIDGING    MANIPULATION. 


6-21 


diameter  of  the  bottles,  and  of  such  a  distance  from  the 
lower  portion,  or  false  bottom,  that  the  flasks  do  not  rise 
above  its  edge,  or  at  least  but  little.  This  deposition  is  to 


FIG.  123. 


FIG.  124. 


protect  the  silver  chloride  from  the  light,  for  it  decomposes 
in  contact  with  water,  and  a  little  hydrochloric  acid  is 
produced,  which  requires  for  its  precipitation  a  certain 
quantity  of  silver  nitrate,  and  so  lowers  the  standard  of 
the  alloy.  This  cause  of  error  is,  however,  not  very  great, 
at  least  when  the  light  does  not  fall  directly  on  the 
chloride. ;  but  it  is  easy  to  avoid,  and  should  not  be  neg- 
lected. The  disposition  already  pointed  out  does  not  at  all 
complicate  the  process,  and  is  moreover  useful,  as  it  pre- 
vents the  fracture  or  upsetting  of  the  bottles.  When  but 
one  bottle  is  operated  on,  it  is  placed  for  Lagitation  in  a 
japanned  tin-plate  cylinder,  which  is  held  as  shown  at  fig. 
124.  On  placing  the  bottles  in  their  respective  places  on 
the  table,  a  brisk  circular  movement  is  given  to  them,  so  as 
to  remove  any  silver  chloride  Fm.  12.-,. 

adhering  to  the  sides  ;  their 
stoppers  are  removed  and  sus- 
pended by  spring  pincers,  a  a. 
These  are  formed  of  sheet-iron 
wire  (see  fig.  125).  A  thou- 
sandth of  the  decime  solution  is  then  poured  into  each 
bottle,  and  before  this  has  been  completed  there  will  have 


622  THE   ASSAY   OF   SILVER. 

formed  in  the  first  bottles  where  there  is  any  precipitate,  a 
well-marked  nebular  layer  about  a  centimetre  in  thickness. 
At  the  back  of  the  table  is  a  black  board,  P  P,  divided 
into  compartments  numbered  from  1  to  10,  on  each 
of  which  is  marked  with  chalk  the  number  of  thousandths 
of  decime  liquid  added  to  the  contents  of  the  corresponding 
bottle.  The  thousandths  of  salt  announcing  augmentation 
of  standard  are  preceded  by  the  sign  -f ,  those  of  silver 
nitrate  by  the  sign  — . 

Lastly,  the  black  board  carries  a  small  shelf  pierced 
with  holes,  1 1,  and  these  receive  the  funnels  or  drain  the 
bottles  ;  on  this  shelf  also  are  fastened  the  pincers  for  sus- 
taining the  stoppers. 

Cleaning  the  Bottles. — The  assays  terminated,  the  liquid 
from  each  flask  is  poured  into  a  large  vessel  in  which  there 
is  always  a  slight  excess  of  common  salt ;  and  when  it  is 
full,  the  clear  supernatant  fluid  is  removed  by  means  of  a 
syphon.  Immediately  will  be  given  the  means  of  reducing 
the  silver  chloride  so  collected  to  the  metallic  state.  The 
bottles,  to  the  number  of  ten,  are  first  rinsed  with  the  same 
water  passed  from  one  to  the  other,  then  a  second,  and  then 
a  third  time  with  fresh  water.  They  are  then  placed  to 
FlG  126.  drain  on  the  board  just  mentioned, 

and  the  stoppers  are  placed  in  a 
stand  by  series  of  tens  (see  figs.  126 
and  115).  It  is  important  to  remark, 
that  when  a  glass  has  been  rinsed 
with  distilled  water,  care  must  be 
taken  not  to  rub  it  with  the  fingers,  for  water  poured  in 
such  a  vessel  would  always  be  clouded  on  the  addition  of 
silver  nitrate.  This  effect  is  due  to  the  chlorides  contained 
in  the  perspiration,  and  is  of  course  more  to  be  guarded 
against  in  summer. 

Reduction  of  Silver  Chloride,  obtained  in  the  Assay  of 
Alloys  by  the  Wet  Method. 

Silver  chloride  can  be  reduced  without  sensible  loss, 
after  having  been  well  washed,  by  plunging  it  into  scraps 


PREPARATION   OF   PURE   SILVER.  623 

of  iron  or  zinc,  and  adding  dilute  sulphuric  acid  in  suffi- 
cient quantity  to  set  up  a  slight  disengagement  of  hydro- 
gen gas.  The  whole  can  be  left  to  itself,  and  in  the  course 
of  a  few  days  the  silver  is  completely  reduced.  This  point 
can  be  easily  determined  by  the  colour  and  nature  of  the 
product,  but  better  still  by  treating  a  small  quantity  with 
ammonia,  which,  if  the  chloride  is  perfectly  reduced,  will 
give  no  precipitate  or  cloudiness  on  treatment  with  an  acid. 
The  chlorine  remains  in  solution  in  the  water  combined 
with  zinc  or  iron.  The  residue  must  now  be  washed  ;  the 
first  washings  are  made  with  acidulated  water,  to  dissolve 
iron  oxide  which  might  have  formed,  and  the  following 
with  ordinary  water  :  after  having  completed  the  washing 
as  much  water  as  may  be  left  is  decanted,  the  mass  dried, 
and  a  little  powdered  borax  added.  Nothing  now  remains 
but  to  fuse  it.  The  powdered  silver  being  voluminous,  it 
is  placed  by  separate  portions  in  the  crucible,  in  propor- 
tion as  it  sinks.  The  heat  should  be  at  first  moderate,  but 
towards  the  end  of  the  operation  should  be  sufficiently 
high  to  reduce  the  silver  and  slag  to  a  state  of  complete 
liquidity.  If  it  be  found  that  not  quite  all  the  chloride 
was  reduced  by  the  iron  or  zinc,  a  little  potassium  or 
sodium  carbonate  may  be  added  to  the  powdered  silver. 
The  standard  of  silver  thus  obtained  is  from  999  to  1000 
thousandths. 

Preparation  of  Pure  Silver. 

Take  the  silver  prepared  as  above,  dissolve  it  in  nitric 
acid,  and  leave  the  solution  some  time  in  perfect  rest  in 
water,  to  deposit  any  gold  it  might  contain.  Decant  the 
solution,  and  precipitate  with  common  salt,  well  wash  the 
precipitate,  and  reduce  it,  when  the  resulting  silver  will  be 
pure. 

M.  Gay  Lussac  here  gives  a  description  of  a  process  for 
the  precipitation  of  chlorine  from  nitric  acid  for  use  in  the 
mode  of  assay  already  described  ;  but  as  that  acid  in  a  state 
of  ordinary  purity  forms  an  article  of  commerce,  and  can  be 
obtained  at  most  operative  chemists,  the  process  will  not  be 
here  reproduced. 


t 

624  THE   ASSAY   OF   SILVER. 


Modifications  required  in  the  Assay  of  Silver  Alloys 
containing  Mercury. 

Whenever  mercury  is  present  in  solution  with  silver,  it 
is  thrown  down  as  insoluble  chloride,  and  the  assay  ren- 
dered inaccurate.  The  presence  of  mercury  in  silver  can 
be  readily  detected  by  the  remarkable  change  which  occurs 
in  silver  chloride  on  exposure  to  light  (viz.  blackening) 
when  free  from  mercury  ;  but  if  the  smallest  quantity  of 
the  latter  metal  be  present,  no  blackening  will  ensue.  This 
source  of  error  was  removed  by  M.  Levol  in  the  following 
manner : — The  sample  being  dissolved,  as  usual,  in  nitric 
acid,  it  was  supersaturated  with  25  cubic  centimetres  of 
caustic  ammonia  ;  the  pipetteful  of  normal  solution  was 
then  added,  and  the  excess  of  ammonia  supersaturated 
with  20  cubic  centimetres  of  acetic  acid,  and  the  operation 
continued  in  the  usual  way. 

Some  little  time  after  the  publication  of  this,  M.  Gay 
Lussac  examined  the  above  process  himself,  and  very  con- 
siderably simplified  it.  He  says  : — '  After  having  confirmed 
by  several  experiments  the  accuracy  of  M.  Level's  pro- 
cess, I  thought  it  might  be  simplified  by  adding  to  the 
nitric  solution  of  silver  the  ammonia  and  acetic  acid  at  one 
and  the  same  time,  but  in  sufficient  quantity  to  saturate 
the  whole  of  the  nitric  acid,  both  that  in  combination  with 
the  silver  and  that  in  the  free  state.  Ten  grammes  of  ammo- 
nium acetate  were  added,  with  a  little  water,  to  the  silver 
dissolved  in  nitric  acid,  and  the  assay  finished  in  the 
ordinary  manner.  The  quantity  indicated  by  synthesis 
was  found  very  accurately,  although  100  thousandths  of 
mercury  had  been  added.'  Finally,  M.  Gay  Lussac  found 
that  10  grammes  of  sodium  acetate,  in  crystals,  also  fully 
answered  the  purpose  ;  and  as  that  is  a  very  cheap  com- 
mercial salt,  it  is  the  best  adapted  for  overcoming  the  diffi- 
culty in  this  class  of  assay,  as  regards  the  presence  of 
mercury. 


METHOD    OF   ASSAYING    SILVEK    BARS. 


625 


FIG.  127. 


Method  of  Taking  the  Assay  from  the  Ingot. 

The  ingots  are  so  rarely  perfectly  homogeneous,  even 
taking  as  a  starting-point  the  standard  950  thousandths, 
that  the  differences  remarked  between  the  assays  of  samples 
made  in  different  places  should 
rather  be  attributed  to  the 
above  cause  than  to  the  assay 
itself.  It  is  important,  there- 
fore, to  take  a  sample  in  a 
uniform  manner,  and  from 
the  same  depth,  on  the  upper 
surface  of  the  ingot  as  on  the 
lower.  This  condition  is  per- 
fectly fulfilled  by  boring  the 
ingots  with  a  kind  of  drill, 
similar  to  that  employed  by 
the  smith,  and  which  is  re- 
presented at  Fig.  127.  The 
ingot,  Z,  is  placed  in  a  copper 
tray,  C ;  and  in  order  to 
retain  the  borings,  which 
might  otherwise  be  thrown 
out,  the  drill,/,  is  surrounded 
by  a  casing,  m,  which  does 
not  impede  its  motion,  and 
stands  freely  on  the  ingot. 
After  a  few  turns  of  the  drill, 
the  nVst  borings,  which  are  not  pure,  are  removed  by 
means  of  a  feather,  and  only  those  following  are  collected 
and  reserved  for  assay.  If  it  be  desirable  to  try  the  lateral 
faces,  it  is  necessary  to  employ  a  pressure  screw,  to  keep 
the  ingot  in  the  position  that  may  be  deemed  necessary. 

• 

Method  of  Assaying  Silver  Bars  adopted  in  the  Assay 
Offices  of  H.M.  Indian  Mints. 

According  to  the  report  of  H.  E.  Busteed,  M.D.,  H.M. 
Madras  Army,  refining  assay  master,  Calcutta  Mint,  the 

s  s 


620  THE   ASSAY    OF    SILVER. 

silver  bars  are  assayed  by  determining  the  silver  as 
chloride.  The  cupellation  assay  is  not  correct  enough  to 
satisfy  the  sellers  and  purchasers  :  the  Gay  Lussac  assay 
is  not  used  because  most  of  the  bullion  contains  mercury, 
lead,  and  other  base  metals  ;  because  a  previous  cupel- 
lation assay  is  required  ;  because  the  high  temperature  of 
the  climate  causes  an  evaporation  of  the  salt  solution  ;  and 
because  a  large  number  of  persons  would  be  necessary  on 
account  of  the  large  daily  number  of  assays. 

The  credit  is  due  to  Mr.  J.  Dodd,  a  former  assay  master 
of  the  Calcutta  Mint  (and  a  surgeon  in  the  Madras  army), 
of  having  encountered  those  difficulties  of  manipulation, 
and  of  having  overcome  them,  inasmuch  as  he  modified 
and  simplified  them,  and  in  short  so  systematised  the 
whole  practical  working  of  the  process  as  to  render  its 
application  to  the  assaying  of  silver,  to  any  amount,  easy, 
accurate,  and  economical. 

The  process  is  technically  known  as  the  '  chloride 
process.'  It  is  thus  described  by  Dr.  Busteed  in  the 
4  Chemical  News  '  for  November  1871 : — 

The  samples  (or  '  musters ')  for  assay  are,  to  save  time, 
first  approximately  weighed  by  an  assistant ;  they  are  then 
placed  (each  sample  in  duplicate)  in  small  shallow  saucers 
of  polished  copper,  and  so  brought  in  batches  of  40  on  a 
board,  containing  in  numerical  order  receptacles  for  the 
little  saucer,  to  the  assay  master,  who,  in  the  delicate  assay 
balance,  exactly  brings  each  sample  to  the  one  required 
weight.* 

As  each  sample  is  weighed,  it  is  transferred  from  the 
platinum  skiff  of  the  balance  to  a  bottle  on  the  left  hand  of 
the  assayer,  by  means  of  a  small  copper  funnel.  The 
bottles  f  for  this  purpose  are  held  in  readiness  for  the 
musters  by  an  assistant,  and,  on  receiving  them,  are 
removed  into  the  laboratory  in  batches  of  six. 

On  being  taken  to  the  laboratory,  they  are  ranged  on 
a  circular  platform  or  turn-table,  and  there  one  of  the 

*  The  amount  of  this  weight  will  be  more  particularly  referred  to  farther  on. 
f  The  chief  appliances  will  be  described  more  fully  at  the  conclusion  of  the 
description  of  the  process. 


THE    CHLORIDE    PROCESS.  627 

(European)  assistants  adds  by  means  of  a  pipette  1^-  drms. 
of  nitric  acid  to  each  bottle,  which  are  then  (without  their 
stoppers)  transferred  to  a  sand-bath  and  exposed  to  a 
considerable  degree  of  heat,  till  solution  of  the  contents  is 
effected. 

The  specific  gravity  of  the  nitric  acid  used  is  generally 
1-200,  i.e.,  in  the  case  of  known  alloys  of  only  copper  and 
silver,  such  as  the  standard  meltings,  coins,  &c.  ;  but 
when  the  nature  of  the  alloy  is  uncertain,  such  as  bazaar 
silver,  or  some  sycee  (where  the  presence  of  mercury  may 
be  suspected),  a  stronger  acid  of  sp.  gr.  1-320  is  used.  It- 
has  been  found,  too,  by  experience,  that  the  chlorides 
from  fine  bar  silver  agglomerate  better  when  the  solution 
has  been  effected  in  the  stronger  acid. 

When  the  samples  have  been  completely  dissolved,* 
the  bottles  are  brought  back  to  the  platform,  and  there 
each  receives  through  a  glass  funnel  *f*  about  six  ounces  of 
cold  distilled  water. 

There  is  then  added  to  each  bottle,  through  a  glass 
pipette  as  before,  1^  drms.  of  hydrochloric  acid,  sp.  gr. 
1-060,  which  immediately  converts  the  silver  present  into 
the  characteristic  white  precipitate  of  silver  chloride,  which 
forms  in  slow-falling  curdy  volumes. 

The  stoppers  (previously  dipped  in  distilled  water)  are 
then  carefully  replaced,  and  the  bottles  are  allowed  to 
stand  for  five  minutes. 

The  bottles  are  next  well  shaken  two  and  two  by  the 
laboratory  workmen  for  three  or  four  minutes,  till  the 
chloride  aggregates  and  rapidly  falls  down  ;  any  particles 
which  may  remain  attached  to  the  neck  or  upper  part  of 
the  bottles  are  washed  down  by  a  quick  circular  motion, 
and  more  distilled  water  being  added  to  within  about 
two  inches  of  the  neck  (great  caution  being  observed  in 
removing  and  returning  the  stoppers),  the  bottles  are  then 
allowed  to  rest  each  in  its  assigned  place  on  the  platform 
for  four  hours. 

*  A  slight  residuum  of  gold,  as  a  black  powder,  is  very  generally  seen. 

t  The  portion  of  this  which  enters  the  neck  of  the  bottlers  protected  or 
sheathed,  with  an  inch  of  india-rubber  tubing,  to  prevent  chipping,  if  struck 
against  the  neck  of  the  bottle. 

8  8  2 


628  THE   ASSAY    OF   SILVEK. 

At  the  expiration  of  that  period,  the  clear  supernatant 
liquid  (blue-coloured  when  copper  is  present)  is  removed 
by  a  glass  syphon,  which  is  lowered  to  within  an  inch  of 
the  deposited  chloride,  the  greatest  care  being  taken  that 
none  of  it  is  drawn  up  into  the  syphon.  As  each  platform 
is  made  to  revolve  on  its  centre,  according  as  each  bottle 
is  syphoned,  the  operator  sitting  in  one  place  brings  the 
platform  round  till  the  next  bottle  in  order  gets  under  the 
syphon,  which  is  thus  in  rotation  lowered  into  each.  The 
fluid  escapes  from  the  long  leg  of  the  syphon  through  a 
funnel  fitted  in  the  table  to  a  jar  placed  underneath. 

After  the  first  syphoning,  the  bottles  are  immediately 
filled  again  with  distilled  water,  and  each  gets  a  quiet  cir- 
cular motion  for  a  few  moments,  and  the  precipitate  is  again 
allowed  to  settle  as  evenly  as  possible ;  this  time  it  will  be 
sufficient  to  allow  them  to  rest  for  two  hours,  when  they 
are  again  syphoned  as  before  and  the  stoppers  returned. 

Under  ordinary  circumstances  these  two  washings  are 
sufficient ;  but  if  the  silver  is  evidently  '  coarse,'  a  third  or 
fourth  washing  is  similarly  given. 

•  t  When  it  is  considered  that  the  chlorides  have  been 
sufficiently  washed,  the  bottles  are  placed  for  half  an  hour 
in  a  reclining  position  on  their  platforms  ;  this  causes  the 
chloride  to  fall  and  settle  to  one  spot,  and  renders  its 
removal  from  the  bottles  more  easy. 

Meantime  a  pneumatic  trough  has  been  got  ready, 
capable  of  containing  a  batch  of  twenty  inverted  bottles ; 
the  trough  is  filled  with  distilled  water  ;  for  each  bottle 
there  is  placed  on  the  floor  of  the  trough  a  small  porcelain 
saucer  holding  a  little  Wedgwood  crucible  or  cup,  each 
numbered  to  correspond  to  the  bottles.  A  laboratory 
workman  then  removes  the  stoppers  from  the  bottles,  and 
hands  them  one  by  one  to  an  assistant  at  the  trough,  who, 
placing  his  forefinger  over  the  mouth  of  each  bottle, 
inverts  it  over  its  corresponding  cup,  and  does  not  remove 
his  finger  till  the  neck  of  the  bottle  has  passed  down 
through  the  water  and  well  into  the  cup  ;  then  the;finger 
being  taken';  away,  the  bulk  of  the  chloride  falls  by  its 
own  weight  to  the  bottom  of  the  cup.'v>J  *;L 


THE    CHLORIDE    PROCESS.  629 

The  bottle  is  held  in  ^  the  position  by  two  rings,  one 
(the  larger)  above  the  other,  which  are  fixed  to  the  sides 
of  the  trough  ;  this  arrangement  retains  each  bottle  in 
situ,  at  the  proper  slant,  and  admits  of  the  operator  gently 
revolving  or  slightly  raising  the  bottle  with  his  left  hand, 
while  with  the  right  he  patiently  taps  the  bottom  and 
sides  till  the  whole  of  the  chloride  has  been  dexterously 
got  out ;  the  finger  is  then  again  placed  over  the  mouth, 
and  the  bottle  raised  up  through  the  rings  and  handed 
(mouth  upwards)  to  the  assayer,  or  to  the  supervising 
assistant  standing  by,  who  carefully  examines  it  to  see 
that  every  particle  of  chloride  has  been  dropped  into  the 
cup.  When  this  part  of  the  manipulation  has  been  neatly 
done,  none  of  the  chloride  falls  over  into  the  saucer  which 
is  placed  as  a  precautionary  measure  under  each  cup. 

When  the  chloride  falls  into  the  cup,  it  is  in  an  uneven 
lumpy  state,  and  not  in  a  favourable  condition  for  being 
uniformly  dried  ;  it  has,  therefore,  next  to  be  broken  up. 
For  this  purpose  the  cups  (containing  the  chlorides,  and 
water  to  the  brim)  on  removal  from  the  trough  are  taken 
in  batches  on  a  tray  to  an  assistant  seated  at  a  steady 
table,  who  first  carefully  decants  off  about  half  the  water, 
and  then  with  a  finely-polished  glass  rod  (four  inches  long 
and  one-third  of  an  inch  thick)  gently  stirs  and  beats  the 
lumpy  precipitate,  while  revolving  the  cup  on  the  table ; 
this  causes  it  to  lie  evenly  and  loosely  at  the  bottom  of 
the  cup  as  a  purplish  grey  powder,  not  too  fine. 

He  next  washes  the  rod  over  the  cup  with  distilled 
water  from  a  drop  bottle,  lest  any  of  the  chloride  may  be 
adhering  to  it,  and  sprinkles  a  drop  or  two  from  it  on 
to  the  surface  of  the  water  in  each  cup,  so  as  to  cause  to 
sink  any  minute  particles  that  may  happen  to  remain 
floating.  He  then,  after  an  interval  of  ten  minutes,  drains 
off  about  three-fourths  of  the  supernatant  water,  which  he 
lets  run  down  the  rod  into  a  vessel  near  him,  and  with  a 
tap  or  two  of  the  rod  on  the  outside  of  the  cup  to  still 
further  loosen  the  deposit,  this  part  of  the  manipulation  is 
concluded. 

The  crucibles  are  next  taken  to  the  drying  furnace, 


630  THE    ASSAY    OF    SILVER. 

where  a  steam  bath  is  ready  to  receive  them  ;  on  the  per- 
forated upper  plate  of  this  they  are  ranged,  and  allowed 
to  remain  for  about  an  hour.  This  gradually,  and  without 
spurting,  frees  the  chlorides  from  moisture,  which  may  be 
known  by  their  caking,  i.e.  leaving  the  sides  of  the  cups 
round  the  edges  and  forming  at  the  bottom  of  each  a 
loose  cake,  resembling  somewhat  a  gun-wad.  The  crucibles 
are  then  arranged  on  a  hot-air  plate  and  there  exposed  to 
a  temperature  of  between  300°  and  350°  (F.)  for  about 
two  hours,  till  thoroughly  dried,  when  they  are  ready  for 
weighing.*  When  the  above  manipulations  have  been 
carefully  and  satisfactorily  gone  through,  each  little  cup 
contains  an  unbroken,  tolerably  firm,  cake  of  chloride  of 
silver,  lying  unattached,  which  admits  of  being  easily 
grasped  with  a  pair  of  forceps,  and  cleanly  lifted  out  of 
the  cup  and  conveyed  to  the  skiff  of  the  assay  balance  in 
which  it  is  weighed.  The  cups  are  generally  brought 
from  the  laboratory  to  the  assay er  at  the  balance  in 
batches  of  eight  or  ten.  A  '  standard,'  synthetically  pre- 
pared of  pure  silver  and  copper,  and  an  assay  pound  of 
pure  silver,  are  introduced  with  each  day's  set  of  assays,, 
and  their  chlorides  dried  with  the  others,  and  the  analysis 
of  them  verified  before  weighing  the  rest.  Occasionally 
these  '  checks '  are  also  fused  and  weighed  in  a  porcelain 
capsule,  but  the  weight  found  never  differs  from  that  of 
the  chloride  merely  dried  as  above. 

Once  or  twice  a  month,  the  silver  is  recovered  from 
the  accumulated  chlorides,  which  are  well  pounded  in  a 
mortar  and  brought  to  a  powder  and  then  mixed  with  a 
proper  proportion  of  chalk  and  charcoal,  and  put  into 
a  wrought-iron  crucible  and  reduced  with  heat.  The 
metallic  silver  so  recovered  is  transferred  to  the  mint. 

Under  the  circumstances  of  the  solution  and  of  the 
precipitation  as  detailed  above,  should  any  gold  happen 
to  be  present  in  the  sample  operated  on,  it  is  not  dissolved, 
and  therefore  becomes  entangled  with  the  precipitated 

*  The  chlorides  are  weighed  warm,  to  obviate  the  risk  of  their  absorbing: 
moisture  ;  a  precaution  especially  necessary  in  the  heavy  monsoon  weather  in 
this  country. 


THE    CHLORIDE    PROCESS.  631 

silver  chloride  and  dried  and  weighed  with  it,  and  ac- 
cordingly comes  to  be  regarded  and  valued  as  silver.  In 
this  the  chloride  process  resembles  that  by  cupellation, 
which  likewise  takes  no  distinguishing  cognisance  of  gold  ; 
and  both  these  processes  contrast  in  this  respect  with  the 
volumetric  one,  which  is  a  rigid  analysis  for  silver  alone  ; 
so  that,  strictly  speaking,  an  assay  conducted  by  either  of 
the  first-named  methods  ascertains  the  proportion  present 
of '  the  precious  metals,'  i.e.  silver  and  gold.* 

Should  mercury  be  present  it  does  not  interfere  with 
the  result,  when  the  solution  has  been  effected  in  excess 
of  nitric  acid  with  strong  heat.  Thus  the  mercury  be- 
comes peroxidised,  and  hydrochloric  acid  forms  no  pre- 
cipitate in  solutions  of  mercuric  salts  ;  any  mercuric 
chloride  resulting  from  the  combination  would  remain 
in  solution,  and  be  washed  away  in  the  course  of  the 
process. 

Should  -lead  happen  to  be  present,  hydrochloric  acid 
gives  no  precipitate  in  a  dilute  solution,  the  lead  chloride 
being  soluble  in  a  certain  proportion  of  distilled  water ; 
but  even  were  the  proportion  of  lead  to  silver  tolerably 
large,  and  the  lead  chloride  happened  to  be  thrown  down, 
the  repeated  washings  would  dissolve  and  get  rid  of  it. 

With  regard  to  the  weight  of  the  small  portion  taken 
to  represent  the  mass,  the  system  prevails  in  the  Indian 
mints  of  taking  samples  for  assay  by  granulating  a  small 
portion  of  the  contents  of  each  melting-pot :  when  the 
metal  is  in  a  thorough  state  of  fusion  and  has  just  been 
well  stirred,  a  small  ladleful  of  the  molten  metal  is  quickly 
poured  from  a  tolerable  height  into  a  vessel  of  water,  and 
the  granules  so  formed  received  on  a  strainer,  lifted  out, 
and  perfectly  dried.f  The  weight  of  this  specimen  repre- 

*  Much  of  the  silver  which  finds  its  way  to  the  Indian  mints  is  rich  in  gold ; 
for  instance,  sycee  contains  on  an  average  somewhat  about  12  grs.  in  the  troy 
pound.  This  in  minting  operations  is  considered  as  silver,  and  as  such  it  enters 
into  the  coinage.  There  being  as  yet  no  refineries  established  here,  through 
which  such  silver  could  pass  to  the  mechanical  departments  of  the  mints,  the 
silver  coins  made  daring  a  period  when  a  heavy  importation  of  sycee  had  been 
worked  up,  contain  as  much  as  4  or  6  grains  of  gold  in  every  32  tolas  or  1  pound 
troy. 

t  The  introduction  into  the  Calcutta  Mint  of  this  system  of  taking  musters 
is  attributable  to  Dr.  Boycott,  late  Assay  Master,  and  *to  Dr.  Shekelton,  who, 


(.32  THE   ASSAY    OF    SILVER. 

senting  each  pot  was  first  fixed  at  24  grs.,  technically 
called  the  '  assay  pound  : '  this,  in  the  case  of  pure  silver, 
yielded  31 '87  grs.  of  silver  chloride,  while  the  same  quan- 
tity of  Indian  standard  silver  (which  is  -fg-ths  silver  plus 
TVth  copper  =  916-66  in  1000)  yielded  -^th  less,  or  29-21 
grs. :  on  the  weight  of  chloride  being  ascertained  in 
each  case,  a  table  which  was  calculated  and  prepared  for 
the  purpose  was  referred  to,  and  the  equivalent  fineness 
assigned  to  the  ^  dwt.,  plus  the  odd  grs.,  when  any.  But 
when  it  became  desirable  to  prepare  for  the  decimal  form 
of  notation,  a  number  more  convenient  than  31-97  was 
looked  for  to  represent  purity  or  1000,  and  25  was  fixed 
on  as  a  desirable  starting-point,  particularly  as  the  quan- 
tity of  pure  silver  yielding  that  amount  of  chloride,  viz., 
18-825  grs.,  was  quite  large  enough  to  represent  each 
pot.* 

The  weight,  therefore,  of  the  '  assay  pound  '  in  use  at 
present  is  18*825  grs.  This  produces  (with  chlorine)  in 
the  case  of  pure  silver  25  grs.  of  silver  chloride,  j* 

But  to  obviate  the  necessity  of  constant  reference  to  a 
calculated  table  to  find  the  equivalent  in  pure  silver  of  the 
amount  of  silver  chloride  found  in  each  case,  it  was  inge- 
niously arranged  to  stamp  each  of  the  assay  weights  not 
with  its  actual  weight,  but  with  the  figures  representing 
the  proportion  per  mille  of  pure  metal  which  such  a 
weight  of  chloride  so  found  corresponds  to  :  thus,  sup- 
by  a  number  of  interesting  experiments,  satisfied  themselves  that  samples  so 
taken  represent  the  mass  of  mixed  metal  to  be  valued  much  more  fairly  than 
samples  of  the  same  mass  cut  or  gouged  from  it  after  it  has  been  poured  and 
allowed  to  cool  in  the  ingot  moulds,  where  a  partial  separation  of  the  copper 
from  the  silver  seems  to  take  place  ;  the  result  being,  according  to  the  above 
experiments,  that  in  the  case  of  ingots  cast  in  upright  moulds  all  the  outside 
is  much  below  the  average  fineness  of  the  mass  on  assay,  and  the  centre  much 
above  it.  This  refers  to  alloys  of  silver  and  copper  mixed  in  or  about  the  pro- 
portion of  '  standard.'  According  to  M.  Level,  however,  it  would  appear  that 
when  an  alloy  of  silver  and  copper  in  which  the  proportion  of  the  latter  is  very 
high  (viz.,  over  28  per  cent.)  has  been  melted,  poured,  and  allowed  to  cool,  an 
opposite  result  to  the  above  is  found,  viz.,  the  outside  of  the  ingots  is  above  the 
average  fineness.  An  assay,  therefore,  from  a  granulated  sample  must  give  a 
much  nearer  approximation  to  truth  than  one  from  a  cut  sample. 

*  The  average  weight  of  the  contents  of  each  melting-pot  is  12,500  tolas,  or 
about  390  pounds  troy,  so  that  the  specimen  taken  to  represent  this  is  but  about 
the  119,000th  part ;  each  sample  is  assayed  in  duplicate. 

t  The  basis  for  these  numbers  was  founded  on  the  proportion  in  which, 
according  to  Turner,  silver  combines  with  chlorine,  viz.,  100  parts  with  32-80. 


THE   CHLORIDE   PROCESS. 


633 


posing  a  melting  of  five-franc  pieces  was  being  assayed, 
and  the  chloride  resulting  from  the  assay  pound  operated 
on  weighed  22 -5  grs.  (showing  the  actual  pure  contents  in 
the  sample  to  be  16*94  grs.),  instead  of  referring  to  a  table 
to  see  the  equivalent  per  mille-age  of  silver,  that  weight 
which  is  actually  22 -5  grs.  has  900  marked  on  it,  and  the 
assayer  simply  reads  the  '  to  ich '  from  it. 

v  Accordingly,  the  assay  weights  are  as  follows  : — 


Actual  weight  in  grs.                                                  Figures  marked  on  the  weights 

25-000 

.     1000-00 

22-910 

(S:d.)      916-66 

22-500 

900-00 

20-000 

800-00 

17-500 

700-00 

15-000 

600-00 

12-500 

500-00 

10-000 

400-00 

7-500 

300-00 

5-000 

200-00 

2-500 

100-00 

1-250 

50-00 

1-000 

40-00 

0-750 

30-00 

0-500 

20-00 

0-250 

10-00 

0-125 

5-00 

0-100 

4-00 

0-075 

3-00 

0-050 

2-00 

0025 

1-00 

Assay  lb.,  weigh t= 18-825  grs. 

An  ordinary  day's  work  consists  of  eighty  assays,*  esti- 
mating imported  bullion  to  the  value  of  four  lacs  of 
rupees,  and  standard  meltings  and  coins  to  the  value  of 
five  lacs.  But  on  emergencies,  in  time  of  heavy  pressure, 
by  working  extra  hours,  as  many  as  164  assays  have  been 
daily  conducted,  estimating  to  the  value  of  eight  lacs  of 
rupees,  and  standard  coins  and  meltings  to  the  value  of 
fourteen  lacs. 

Such  is  an  outline  of  the  method  of  assay  worked  on  a 
large  scale  ;  of  course  successful  results  from  it  cannot  be 
-expected  unless  each  step  in  the  manipulation  be -con- 
ducted with  great  care  and  accuracy,  and  only  then  after 
much  practice  and  experience. 

*  Exclusive  of  any  gold  assays  which  may  be  going  on. 


634  THE   ASSAY    OF    SILVER. 

The  natives  of  this  country  possess  great  aptitude  in 
acquiring  the  skill  and  consequent  lightness  of  touch  so 
essential  for  delicate  manipulation ;  this,  added  to  their 
characteristic  patience,  makes  them  admirable  subordi- 
nates in  an  assay  laboratory,  under  judicious  supervision  ; 
moreover,  their  labour  is  cheap  ;  so  that,  on  the  whole, 
the  process  seems  to*  be  especially  suitable  for  an  Indian, 
mint. 

When  bar  silver  is  imported  from  the  Continent,  the 
assays  of  it,  made  here,  almost  invariably  correspond  most 
closely  with  those  previously  made  of  it  in  Paris  by  the 
volumetric  method.  But  were  further  proof  needed  of 
the  practical  accuracy  of  this  system,  it  is  to  be  found  in 
the  very  close  proximity  to  the  legal  standard  at  which 
the  large  Indian  coinage  has  been  maintained  for  many 
years,  as  annually  reported  by  the  assayers  to  the  Eoyal 
Mint  of  Great  Britain,  who  test  the  fineness  of  the  Indian 
pyx  coins  by  the  French  wet  process. 

Without  this  method  (improved  and  made  more  per- 
fect, as  it  has  been,  in  the  hands  of  successive  assay 
officers),  it  would  have  been  very  difficult  for  the  assay 
establishments  of  the  Indian  mints  to  have  dealt  with,  in 
the  same  time  and  with  the  same  accuracy,  the  immense 
importation  of  silver  to  India  during  the  last  fifteen  years. 
In  the  single  year  1865-66  there  was  poured  into  the 
Indian  mints,  and  manufactured  into  coin,  silver  alone 
reaching  in  value  to  the  prodigious  amount  of  over  four- 
teen millions  sterling. 

The  system  which  enabled  the  assay  officers  to  value 
such  a  rapid  and  heavy  influx  with  accuracy,  and  with 
satisfaction  to  the  importer  on  the  one  hand,  and  to  the 
mint  (the  buyer)  on  the  other,  and  to  faithfully  maintain 
the  immense  resulting  coinage  close  to  legal  standard,  has 
been  put  to  a  severe  test.  If  success  be  the  criterion  of 
merit,  the  twenty  years'  large  experience  of  this  method 
gained  in  the  Indian  mints  goes  to  show  that  it  is  worthy 
of  a  yet  wider  field  of  utility. 


THE    CHLORIDE    PROCESS.  635 


Apparatus  and  Appliances  required. 

(1.)  The  bottles  used  in  this  process  are  of  thin  (but 
strong)  white  glass,  and  contain  about  12  fluid  oz. ;  about 
6  inches  in  height  and  2^  inches  in  diameter  at  the  bottom, 
which  should  present  a  perfectly  even,  level  floor ;  they 
are  without  any  (abrupt)  shoulder,  but  become  gradually 
pyramidal  from  about  half-way  up  to  the  neck  ;  this  shape 
favours  the  easy  dropping  out  of  the  chloride.  The  neck 
is  about  one  inch  in  length,  polished  on  its  inner  surface ; 
the  stoppers  are  of  ground  glass,  polished,  with  globular 
heads,  and  are  made  to  fit  with  the  utmost  accuracy  and 
smoothness.  The  bottles  and  stoppers  are  numbered,  to 
correspond  with  the  number  on  the  muster  board  and  also 
on  the  cups. 

(2.)  The  '  cups '  are  Wedgw^ood  crucibles,  smooth  and 
thin,  about  1^  inches  in  height,  1^  inches  in  diameter 
above,  and  a  little  less  than  1  inch  in  outside  diameter  at 
the  bottom.  The  floor  should  be  perfectly  level,  and 
neither  it  nor  the  sides  should  present  any  roughness  likely 
to  retain  the  chloride.  The  cups  are  all  numbered. 

(3.)  The  porcelain  saucers  are  shallow,  f  of  an  inch  in 
depth  ;  the  upper  diameter  is  about  4  inches,  the  lower  2^ 
inches. 

(4.)  The  turn-table  is  a  circular  board  of  about  3  feet 
in  diameter,  fenced  by  a  brass  railing  (or  by  a  simple  ledge) ; 
its  centre  is  occupied  by  a  raised  platform  about  2  feet  in 
diameter,  between  which  and  the  rail  the  bottles  (26  on 
each)  stand,  the  round  outer  edge  of  the  platform  having 
semi-lunar  niches  cut  in  it,  into  which  the  bottles  fit ; 
opposite  to  each  niche  on  the  platform  is  a  little  concavity 
in  which  the  stoppers  rest  when  not  in  the  bottles.  Each 
turn-table  is  made  to  revolve  on  its  centre  in  either  direc- 
tion, and  is  raised  about  6  inches  above  the  long  general 
table  on  which  all  are  supported ;  close  to  each  a  funnel 
is  fitted  into  the  lower  (supporting)  table  for  conducting 
away  the  fluid  syphoned  from  each  set  of  bottles. 

(5.)  The  trough  is  a  basin  of  cast-iron  (painted) ;  it 


636  THE    ASSAY    OF    SILVER. 

may  be  oblong  or  round,  raised  to  about  the  height  of 
3  feet  from  the  ground ;  when  round  and  large  enough 
for  twenty  bottles,  space  and  distilled  water  may  be 
economised  by  having  a  platform  insulated  in  the  centre. 
This  is  convenient  for  resting  the  bottles  on  after  the 
chlorides  have  been  got  out.  A  trough  of  this  kind  may 
be  about  2^  feet  in  diameter,  having  a  space  7  inches 
broad  and  4  deep  all  round  between  the  circumference  of 
the  basin  itself  and  the  outer  edge  of  the  island  platform. 
Into  this  space  is  poured  distilled  water  to  the  depth  of 
3  inches.  From  the  rim  of  the  trough  hang  as  many 
brass  supports  as  there  are  bottles  to  be  inverted  ;  there 
are  two  circular  clasps  connected  at  the  back  to  a  bar 
common  to  both  ;  one,  the  larger,  is  1^  inches  above  the 
smaller  and  lower  one,  which  is  under  water  ;  they  are 
open  in  front  (or  towards  the  centre  of  the  basin)  to  about 
1  of  an  inch  in  width.  The  openings  of  both  are  in  the 
same  line,  owing  to  the  lower  (smaller)  segment  being 
projected  towards  the  centre  by  an  abrupt  curve  in  the 
connecting  bar,  by  which  they  hang  from  the  brim.  This 
arrangement  receives  and  fixes  the  inverted  bottles  in  the 
required  position.  The  distilled  water  is  removed  from 
the  trough  by  the  withdrawal  of  a  plug.  These  troughs 
are  sometimes  made  to  revolve  on  the  centre. 

(6.)  The  drop  bottle  used  for  washing  down  the  glass 
rod  when  breaking  up  the  chlorides,  and  for  sprinkling  the 
surface  of  the  cups,  is  small-sized,  round,  so  as  to  be  easily 
grasped ;  it  holds  about  6  ozs.  The  stopper  is  hollow, 
with  two  small  tubes  leading  from  its  head ,  one  opposite  to 
the  other.  Glass  is  so  liable  to  break  or  chip,  that  a  hollow 
silver  stopper  is  now  generally  substituted. 

(7.)  The  steam-bath  is  simply  a  square  vessel  made 
of  sheet  copper,  between  3  and  4  inches  deep,  the  top  or 
upper  plate  of  which  has  a  number  of  circular  openings 
about  two-thirds  of  the  diameter  of  a  Wedgwood  crucible. 
There  is  also  a  steam  escape  pipe  leading  from  the  centre 
below  to  about  a  foot  in  height.  They  are  of  various  sizes, 
to  contain  from  10  to  150  pots :  they  are  raised  or  moved 
by  two  lateral  handles. 


THE   CHLORIDE    PROCESS.  637 

(8.)  Hot-air  plate  of  thin  sheet  iron  bored  with  holes 
for  the  reception  of  the  crucibles,  raised  by  iron  feet  about 
1^  inch  above  the  furnace  plate.  It  is  furnished  with  a 
square  tin  cover,  which  fits  over  it.  This  is  provided  with 
lateral  apertures  for  the  escape  of  heated  air,  and  with  a 
tube  from  its  roof  for  the  reception  of  a  thermometer. 

The  drying  furnace  on  which  the  above  rest  is  sur- 
mounted by  a  hood,  the  door  of  which  (glazed)  slides  up 
and  down  by  weights  and  pulleys  ;  the  plate  is  heated  by 
means  of  gas  jets  ;  it  has  a  good  draught  to  carry  off  the 
nitrous  fumes,  as  on  it  the  musters  are  dissolved  in  the  first 
instance  on  a  sand  bath. 

(9.)  The  forceps  for  removing  the  cake  of  chloride 
from  each  cup  to  the  skiff  of  the  balance  should  not  be  too 
sharp  in  its  grasp  ;  it  is  much  improved  by  having  the 
blades  tipped  for  about  an  inch  from  the  points  with 
platinum  about  -J-  inch  in  width. 

(10.)  It  is  a  convenience  to  have  the  assay  weights 
arranged  in  a  set  of  ivory  compartments  in  the  weight 
box  ;  on  the  floor  of  each  compartment  are  engraved  the 
figures  corresponding  to  those  engraved  on  the  weight 
which  occupies  it ;  by  this  means  the  assay er  has  merely 
to  glance  at  his  weight  box  to  see  what  weights  are  in  the 
pan  of  the  balance,  and  to  read  off  the  '  touch  '  when  each 
chloride  is  counterpoised. 

Mr.  J.  Yolhard  gives  ('  Liebig's  Annalen  ')  the  following 
process  for  the  volumetric  assay  of  silver  by  means  of  a 
solution  of  ammonium  sulphocyanide. 

In  a  nitric  solution  of  silver  to  which  a  soluble  ferric 
salt  has  been  added,  a  permanent  redness  does  not  appear 
on  the  gradual  addition  of  a  dilute  solution  of  ammonium 
or  potassium  sulphocyanide,  until  all  the  silver  has  been 
thrown  down  as  a  sulphocyanide.  If  we  know  how  much 
of  the  suiphocyanide  solution  is  required  to  precipitate  a 
known  weight  of  silver  we  can  determine  volumetrically 
the  quantity  of  silver  present  in  any  acid  argentic  solution, 
the  ferric  salt  serving  as  an  indicator.  For  the  preparation 
of  the  standard  solution  the  author  uses  ammonium  sul- 
phocyanide, though  Lindermann  prefers  the  potassium 


638  THE    ASSAY    OF    SILVER. 

salt ;  both  in  dilute  solution  are  permanent.  But  the  am- 
monium salt  is  less  frequently  contaminated  with  chlorides, 
which  interfere  greatly  if  present  in  more  than  mere  traces. 
The  solution  may  be  conveniently  made  of  such  a  strength 
that  1  c.c.  indicates  1  centigramme  of  silver.  The  weighed 
quantity  of  the  salt  is  dissolved  in  water,  and  diluted  in  a 
graduated  flask  so  far  that  7 '5  grms.  (or  8  grms.  if  the 
salt  appears  very  damp)  may  be  contained  in  each  litre. 
For  the  precipitation  of  1  grm.  of  silver  0-704  grm.  of 
pure  ammonium  sulphocyanide  is  requisite  ;  0'5  grm.  of 
chemically  pure  silver  is  then  weighed  out,  dissolved  in  8 
to  10  c.c.  of  pure  nitric  acid  of  sp.  gr  1*20,  and  after  the 
complete  solution  of  the  metal,  the  nitrous  acid  is  expelled 
by  boiling  or  prolonged  heating  on  the  sand-bath,  and  the 
solution  is  allowed  to  cool.  It  is  then  diluted  with  200 
c.c.  of  water,  and  5  c.c.  of  a  cold  saturated  solution  of 
ammonia-iron  alum  are  added.  If  the  colour  of  the  ferric 
salt  is  perceptible,  a  little  pure  colourless  nitric  acid  is 
added  till  it  disappears.  The  sulphocyanide  solution  is 
then  added  from  a  burette.  At  first  a  white  precipitate  is 
produced,  which  remains  suspended  in  the  liquid  like  silver 
chloride,  rendering  it  milky.  On  the  further  addition  of 
sulphocyanide  each  drop  produces  a  blood-red  cloud,  which 
quickly  disappears  on  agitation.  As  the  point  of  satura- 
tion is  reached,  the  silver  sulphocyanide  collects  in  flocks, 
and  the  liquid  grows  clearer,  without  becoming  perfectly 
limpid,  as  long  as  a  trace  of  silver  remains  in  solution.  As 
soon  as  all  the  silver  is  precipitated  the  flocculent  precipi- 
tate quickly  deposits,  and  the  supernatant  liquid  becomes 
quite  clear.  The  sulphocyanide  solution  is  added  by  drops 
till  this  point  is  attained,  and  till  a  very  faint  light  brown 
colour  appears  in  the  liquid,  which  does  not  vanish  on 
repeated  agitation.  The  colour  is  most  easily  perceived 
if  the  liquid  is  held,  not  up  to  the  light,  but  against  a  white 
wall  turned  away  from  the  window. 

For  a  repetition  of  the  experiment  it  is  convenient  to 
use  a  silver  solution  of  a  known  strength.  For  this  pur- 
pose 10  grms.  of  pure  silver  are  dissolved  in  nitric  acid 
in  a  litre  flask,  the  nitrous  acid  is  expelled,  the  liquid  is 


THE    CHLORIDE    PROCESS.  039 

allowed  to  cool,  and  diluted  up  to  the  volume.  For  use 
-50  c.c.  are  taken  with  a  pipette.  If  the  above-mentioned 
proportions  are  preserved  for  0*5  grm.  silver,  or  50  c.c.  of 
the  silver  solution,  somewhat  less  than  50  c.c.  of  the  sul- 
phocyanide solution  will  be  required,  whence  the  needful 
dilution  can  be  calculated.  If  48*5  c.c.  sulphocyanide 
have  been  used,  then  to  every  48*5  c.c.  of  the  solution  15 
c.c.  of  water  must  be  added. 

The  solution  is  perfectly  permanent,  even  on  being 
kept  for  two  years.  The  silver  solution  must  have  a 
decidedly  acid  reaction  from  free  nitric  acid,  which  it  is 
quite  unnecessary  to  neutralise,  for  it  is  important  that 
the  proportion  of  acid  in  different  experiments  should  be 
approximately  equal.  It  is,  however,  essential  for  the  con- 
stancy of  the  results  that  the  ferric  salt  should  be  in  large 
excess,  and  should  be  used  approximately  in  one  and  the 
same  proportion  to  the  total  volume  of  the  fluid.  It  must 
also  be  remembered  that  the  colour  of  ferric  sulphocyanide 
is  destroyed  by  nitrous  acid  at  common  temperatures,  and 
by  nitric  acid  on  the  application  of  heat.  Hence  follows 
the  necessity  of  completely  expelling  all  nitrous  acid,  and 
of  allowing  the  liquid  to  become  cold  before  the  operation 
is  begun.  The  nitric  acid  used  in  this  process  should  be 
kept  in  the  dark. 


Titration  of  Silver  in  Presence  of  other  Metals. 

Copper. — The  proportion  of  copper  in  an  alloy  may 
reach  70  per  cent,  without  in  the  least  affecting  the  accu- 
racy of  the  process.  Beyond  this  limit  the  recognition  of 
the  final  reaction  is  somewhat  doubtful,  since  after  the 
precipitation  of  the  silver  the  liquid  is  rendered  opaque 
and  discoloured  by  the  formation  of  black  copper  sulpho- 
cyanide. The  only  remedy  in  such  cases  is  to  add  a 
known  weight  of  pure  silver  to  the  alloy,  so  as  to 
reduce  the  proportion  of  copper  below  70  per  cent.,  as  is 
done  in  Gay-Lussac's  process. 

Mercury. — In  presence  of  this  metal  silver  cannot  be 


640  THE    ASSAY    OF    SILVER. 

titrated  with  sulphocyanide  solution.     This  defect  is  of 
little  consequence,  as  mercury  is  readily  expelled. 

Palladium  renders  the  titration  of  silver  with  sulpho- 
cyanide inaccurate,  this  metal  appearing  in  the  result  as 
silver.  This  is  an  important  circumstance  from  a  technical 
point  of  view,  since  palladium;  though  frequently  present 
in  silver,  occurs  in  very  small  quantities. 

As  regards  other  metals  soluble  in  nitric  acid  and 
found  along  with  silver  in  alloys  and  ores,  lead,  cadmium, 
thallium,  bismuth,  zinc,  iron,  and  manganese  are  without 
influence.  The  recognition  of  the  final  reaction  in  solu- 
tions strongly  coloured  by  salts  of  cobalt  or  nickei, 
requires  some  practice.  At  first  a  few  drops  of  sulpho- 
cyanide will  always  be  added  in  excess.  It  is  then  recom- 
mended to  titrate  back  with  a  solution  of  silver,  when  the 
pure  colour  of  the  cobalt  or  nickel  will  appear  so  suddenly 
and  distinctly,  that  it  will  conversely  be  easy  to  seize  the 
exact  point,  when  the  colour  of  the  solution  is  modified 
to  a  yellowish  brown  by  the  addition  of  the  colour  of  fer- 
ric sulphocyanide.  When  the  change  of  shade  has  been 
observed  four  or  five  times  by  titrating  backwards  and 
forwards  with  exactly  corresponding  solutions  of  silver 
and  of  sulphocyanide,  such  a  certainty  in  the  recognition 
of  the  final  reaction  will  be  attained  that  there  can  be  no 
doubt  as  to  the  addition  of  a  half  drop  more  or  less. 

The  presence  of  tin,  antimony,  and  arsenic  does  not 
interfere  with  the  accuracy  of  the  process. 

Mr.  C.  A.  M.  Balling  gives  the  following  instructions 
for  the  direct  determination  of  silver  in  galena  by  Vol- 
hard's  process  : — From  2  to  5  grms.  of  the  galena,  accord- 
ing to  its  supposed  richness  in  silver,  are  very  finely  ground 
and  intimately  mixed  in  a  porcelain  mortar  with  from 
three  to  four  times  its  weight  of  a  flux  composed  of  equal 
parts  of  soda  and  saltpetre,  placed  in  a  porcelain  crucible, 
covered,  and  heated  over  a  burner  to  thorough  fusion, 
when  the  mixture  is  well  stirred  with  a  glass  rod.  It  is 
then  let  cool  and  placed  in  an  evaporating  dish  partly 
filled  with  water,  in  which  the  melted  matter  is  softened, 
dissolved  out  of  the  crucible  into  the  dish,  which  is  then 


FORBES'S   BLOWPIPE   ASSAY.  641 

heated,  and  the  watery  solution  is  filtered  into  a  flask. 
The  residue  on  the  filter,  after  being  well  washed,  is  rinsed 
back  into  the  dish,  very  dilute  nitric  acid  is  added,  and 
the  whole  evaporated  to  dryness.  The  dry  residue  is 
taken  up  in  water  acidulated  with  nitric  acid,  heated,  and 
filtered  into  the  same  flask  in  which  is  the  aqueous  solu- 
tion. The  residue  is  washed  with  hot  water,  the  filtrate 
is  allowed  to  cool  in  the  flask,  ferric  sulphate  or  iron 
alum  is  added,  and  the  liquid  is  titrated. — Oest.  Zeitschrift 
Bergu.  Hutten. 

BLOWPIPE   ASSAY   OF   SILVER. 

The  following  very  complete  method  for  the  blowpipe 
assay  of  silver  and  its  ores  is  given  by  David  Forbes, 
F.K.S.,  in  the  <  Chemical  News/  Nos.  380,  384,  392,  396, 
398,  and  412. 

The  blowpipe  assay  of  silver  ores  was  first  described 
in  1827  by  Harkort,*  and  subsequently  considerably  im- 
proved by  Plattner.  This  assay  process  is  in  all  cases 
based  upon  the  reduction  to  a  metallic  state  of  all  the 
silver  contained  in  the  compound  in  question  along  with 
more  or  less  metallic  lead,  which  latter  metal,  when  not 
already  present  in  sufficient  quantity  in  the  substance 
itself  under  examination,  is  added  in  the  state  of  granu- 
lated lead  to  the  assay  previous  to  its  reduction.  The 
globule  of  silver-lead  thus  obtained,  if  soft  and  free  from 
such  elements  as  would  interfere  with  its  treatment  upon 
the  cupel,  may  then  be  at  once  cupelled  before  the  blow- 
pipe until  the  pure  silver  alone  remains  upon  the  bone-ash 
surface  of  the  cupel ;  but  if  not,  it  is  previously  submitted 
to  a  scorifying  or  oxidising  treatment  upon  charcoal  until 
all  such  substances  are  either  slagged  off  or  volatilised, 
and  the  resulting  silver-lead  globule  cupelled  as  before. 

As,  therefore,  the  final  operation  in  all  silver  assays  is- 
invariably  that  of  cupelling  the  silver-lead  alloy  obtained 
from  the  previous  reduction  of  the  substance,  effected  by 
methods  differing  according  to  the  nature  of  the  argen- 

*  'Die  Probirkunst  mit  dem  Lochrohra. '     Freiberg,  1827,  I.  Heft  (all 
published). 

T   T 


642 


THE   ASSAY   OF   SILVER. 


tiferous  ore  or  compound  under  examination,  it  is  here  con- 
sidered advisable  to  introduce  the  description  of  the  silver 
assay  by  an  explanation  of  this  process. 

In  the  ordinary  process  of  cupellation  in  the  muffle, 
bone-ash  or  other  cupels  are  employed  of  a  size  large 
enough  to  absorb  the  whole  of  the  litharge  produced  from 
the  oxidation  of  the  lead  in  the  assay. 

This,  however,  should  not  be  the  case  when  using  the 
blowpipe ;  for  as  the  heating  powers  of  that  instrument 
are  limited,  it  is  found  in  practice  much  better  to  accom- 
plish this  result  by  two  distinct  operations — the  first  being 
a  concentration  of  the  silver-lead  in  which  the  greater 
part  of  the  lead  is  converted  by  oxidation  into  litharge  re- 
maining upon,  but  not,  or  only  very  slightly,  absorbed  by, 
the  bone-ash  cupel :  and  the  second  in  cupelling  the  small 
concentrated  metallic  bead  so  obtained  upon  a  fresh  cupel 
until  the  remaining  lead  is  totally  absorbed  by  the  cupel 
and  the  silver  left  behind  in  a  pure  state.  By  this  means  a 
much  larger  weight  of  the  silver-lead  alloy  can  be  submitted 
to  assay,  and,  for  reasons  hereafter  to  be  explained,  much 
more  exact  results  are  obtained  than 
would  be  the  case  when  the  cupella- 
tion is  conducted  at  one  operation  in 
the  ordinary  manner. 

The  apparatus  used  by  the  author 
for  these  operations  are  shown  to  a 
scale  of  one-half  their  real  size  in  the 
woodcuts  Fig.  128  (a  to  d). 

In  Fig.  128,  a  represents  in  section  a 
small  cylindrical  mould  of  iron,  seven- 
tenths  of  an  inch  in  diameter,  and 
about  four-tenths  high,  in  which  is 
turned  a  cup-shaped  nearly  hemisphe- 
rical depression  two-tenths  of  an  inch 
deep  in  centre,  the  inner  surface  of  which  is  left  rough,  or 
marked  with  minute  ridges  and  furrows  for  the  purpose  of 
enabling  it  to  retain  more  firmly  the  bone-ash  lining  which 
is  stamped  into  it  by  means  of  the  polished  bolt,  also  shown 
in  the  figure.  This  mould  rests  upon  the  stand  d,  having 


FIG.  128. 


FORBES  S   BLOWPIPE   ASSAY.  64:3 

for  this  purpose  a  small  ^central  socket  in  its  base,  into 
which  the  central  pivot  of  the  stand  enters.  This  socket 
is  seen  in  the  ground  plan,  6,  of  the  base  of  the  mould, 
which  shows  likewise  three  small  grooves  or  slots  made  to 
enable  a  steady  hold  to  be  taken  of  it,  when  hot,  by  the 
forceps.  The  stand  itself  is  composed  of  a  small  turned 
ivory  or  wood  base,  fixed  into  a  short  piece  of  strong  glass 
tubing,  which,  from  its  non-conducting  powers,  serves  as  an 
excellent  handle.  In  the  centre  of  the  base  a  slight  iron 
rod  rising  above  the  level  of  the  glass  outer  tube  serves  as 
a  support  for  the  cupel  mould,  into  the  socket  in  the  base 
of  which  it  enters. 

Bone-ash  is  best  prepared  by  burning  bones  which  have 
previously  been  boiled  several  times,  so  as  to  extract  all 
animal  matter.  The  best  bone-ash  is  made  from  the  core- 
bone  of  the  horns  of  cattle  well  boiled  out  and  burned. 
The  ash  from  this  is  more  uniform  than  from  the  other 
bones,  which  have  in  general  a  very  compact  enamel-like 
exterior  surface,  whilst  the  interior  is  of  a  much  softer 
nature. 

Concentration  of  the  Silver-lead. — A  cupel  is  prepared 
by  filling  the  above  described  cupel  mould  with  bone-ash 
powder  not  finer  than  will  pass  through  a  sieve  containing 
from  forty  to  fifty  holes  in  the  linear  inch,  and  should  be 
well  dried  and  kept  in  an  air-tight  bottle,  and  the  whole 
pressed  down  with  the  bolt,  using  a  few  taps  of  the  hammer. 
It  is  then  heated  strongly  in  the  oxidising  blowpipe  flame, 
in  order  to  drive  off  any  hygroscopic  moisture.  The  bone- 
ash  surface  of  the  cupel,  after  heating,  should  be  smooth, 
and  present  no  cracks  ;  if  the  reverse,  these  may  be  re- 
moved by  using  the  bolt  again  and  reheating.*  The  silver- 
lead,  beaten  on  the  anvil  into  the  form  of  a  cube,  is  placed 
gently  upon  the  surface  of  the  bone-ash,  and,  directing  a 
pretty  strong  oxidising  flame  on  to  its  surface,  it  is  fused, 
and  quickly  attains  a  bright  metallic  appearance,  and 
commences  to  oxidise  with  a  rapid  rotatory  movement. 

*  These  precautions  are  very  important,  as  the  slightest  trace  of  moisture  in 
the  substance  of  the  bone-ash  would  inevitably  cause  a  spurting  of  the  metal 
during  the  operation. 

T   T   2 


644  THE   ASSAY   OF   SILVER. 

(Occasionally,  when  the  assay  is  large,  and  much  copper  or 
nickel  present,  the  globule  may,  under  this  operation,  cover 
itself  with  a  crust  of  lead  oxide  or  solidify  ;  in  such  cases 
direct  the  blue  point  of  a  strong  flame  steadily  on  to  one 
spot  on  the  surface  of  the  lead  globule,  until  it  commences 
oxidising  and  rotating.  In  some  cases  where  much  nickel 
is  present,  an  infusible  scale,  impeding  or  even  preventing 
this  action,  may  form,  but  will  disappear  on  adding  more 
lead — say  from  three  to  six  grains,  according  to  the  thick- 
ness of  this  scale  or  crust.)  When  this  occurs  the  cupel 
is  slightly  inclined  from  the  lamp,  and  a  fine  blue  point 
obtained  by  placing  the  blowpipe  nozzle  deeper  into  the 
flame,  and  the  lamp  is  directed  at  about  an  angle  of  30° 
on  to  the  globule — not,  however,  so  near  as  to  touch  it 
with  the  blue  point,  but  only  with  the  outer  flame,  so 
moderating  it  as  to  keep  the  assay  at  a  gentle  red  heat, 
and  not  allowing  the  rotation  to  become  too  violent. 

This  oxidising  fusion  should  be  carried  on  at  the  lowest 
temperature  sufficient  to  keep  up  the  rotatory  movement, 
and  to  prevent  a  crust  of  litharge  accumulating  upon  the 
surface  of  the  globule,  but  still  sufficiently  high  to  hinder 
the  metallic  globule  from  solidifying.  Should  this,  how- 
ever, happen,  a  stronger  flame  must  be  employed  for  a 
moment  until  the  metal  is  again  in  rotation  ;  such  inter- 
ruptions should,  however,  be  avoided.  The  proper  tem- 
perature can  only  be  learned  by  practice.  A  too  high 
temperature  is  still  more  injurious,  causing  the  lead  to 
volatilise,  and,  if  rich  in  silver,  c<irry  some  of  that  metal 
mechanically  along  with  it.  The  litharge,  also,  instead  of 
remaining  on  the  cupel,  would  be  absorbed  by  the  bone- 
ash,  and  as  the  surface  of  the  metallic  globule  is  covered 
by  a  too  thin  coating  of  fused  litharge,  some  silver  may  be 
absorbed  along  with  the  litharge.  In  this  operation,  in 
order  to  avoid  loss  of  silver,  the  fused  globule  should  be 
always  kept  in  contact  with  the  melted  litharge. 

By  the  above  treatment,  the  air  has  free  access  to  the 
assay,  and  the  oxidation  of  the  lead  and  associated  foreign 
metals  goes  on  rapidly.  The  surface  of  the  melted  globule, 
when  poor  in  silver,  shows  a  brilliant  play  of  iridescent 


FORBES'S   BLOWPIPE   ASSAY.  645 

colours,  which  does  not  take  place  when  very  rich  in  silver. 
The  litharge  is  driven  to  the  edge  of  the  globule,  heating 
itself  up  and  solidifying  behind  and  around  it.  When  the 
globule  becomes  so  hemmed  in  by  the  litharge  as  to  present 
too  small  a  surface  for  oxidation,  the  cupel  is  moved  so  as 
to  be  more  horizontal  (having  been  previously  kept  in  an 
inclined  position),  thus  causing  the  lead  globule  to  slide 
by  its  own  weight  on  one  side,  and  expose  a  fresh  surface 
to  the  oxidising  action.  When  the  lead  is  pure,  the  litharge 
formed  has  a  reddish-yellow  colour,  but  if  copper  is 
present  it  is  nearly  black. 

In  concentrating  silver-lead,  it  must  be  remembered 
that  an  alloy  of  lead  and  silver,  if  in  the  proportion  of 
about  86  per  cent,  silver  along  with  14  per  cent,  lead, 
when  cooled  slowly  in  the  litharge  behaves  in  a  manner 
analogous  to  the  spitting  of  pure  silver,  throwing  out  a 
whitish-grey  pulverulent  excrescence  rich  in  silver.  For 
this  reason,  therefore,  the  concentration  above  described 
should  be  stopped  when  the  globule  is  supposed  to  contain 
about  six  parts  silver  along  with  one  part  in  weight  of 
lead.  In  case,  however,  this  limit  should  have  been  ex- 
ceeded, it  is  advisable  at  once  to  push  the  concentration 
still  further  until  the  silver  globule  contains  but  very  little 
lead.  In  practice  with  poor  ores  it  is  usual  to  concentrate 
the  lead  until  the  globule  is  reduced  to  the  size  of  a  small 
mustard-seed,  or  in  rich  ores  to  some  two  or  three  times 
that  size.  Upon  arriving  at  this  point,  the  cupel  is  with- 
drawn very  gradually  from  the  flame,  so  that  the  cooling 
shall  take  place  as  slowly  as  possible  until  the  globule  has 
solidified  in  its  envelope  of  litharge.  If  cooled  too  quickly, 
the  litharge,  contracting  suddenly,  would  throw  out  the 
globule,  or  even  cause  it  to  spirt ;  in  such  case  it  should 
be  touched  by  the  point  of  the  blue  flame  so  as  to  fuse  it 
to  a  round  globule,  which  is  cooled  slowly,  as  before  de- 
scribed. The  globule  is  now  reserved  for  the  next  opera- 
tion, for  which  purpose  it  is,  when  quite  cold,  extracted 
from  the  litharge  surrounding  it. 

Cupellation. — The  bone-ash  required  for  this  process 
should  be  of  the  best  quality  and  in  the  most  impalpable 


64$  THE    ASSAY   OF   SILVER 

powder,  prepared  by  elutriating  finely-ground  bone-ash, 
and  drying  the  product  before  use. 

The  cupel,  still  hot  from  the  last  operation,  is  placed 
upon  the  anvil,  and  the  crust  of  litharge,  with  its  enclosed 
metallic  bead,  gently  removed,  leaving  the  hot  coarse  bone- 
ash  beneath  it  in  the  mould  ;  upon  this  a  small  quantity 
of  the  elutriated  bone-ash  is  placed,  so  as  to  fill  up  the 
cavity,  and  the  whole,  whilst  hot,  stamped  down  by  the  bolt, 
previously  slightly  warmed,  with  a  few  taps  of  the  ham- 
mer. The  cupel  thus  formed  is  heated  strongly  in  the 
oxidising  flame,  which  should  leave  the  surface  perfectly 
smooth,  and  free  from  any  fissures  or  scales  ;  if  such 
appear,  the  bolt  must  again  be  used,  and  the  cupel  re- 
heated. In  this  process  it  is  very  important  that  the  cupel 
should  possess  as  smooth  a  surface  as  possible,  whilst  at 
the  same  time  the  substance  of  the  cupel  beneath  should 
not  be  too  compact,  so  as  thereby  to  permit  the  litharge 
to  filter  through  and  be  readily  absorbed,  leaving  the  silver 
bead  upon  the  smooth  upper  surface. 

The  bead  of  silver-lead  obtained  from  the  last  operation 
is  taken  out  of  the  litharge  in  which  it  is  embedded,  and, 
after  removing  any  trace  of  adherent  bone-ash  or  litharge, 
is  slightly  flattened  to  prevent  its  rolling  about  upon  the 
surface  of  the  cupel. 

It  is  now  put  into  the  cupel  prepared  as  before  de- 
scribed, placing  it  on  the  side  furthest  from  the  lamp  and 
a  little  above  the  centre  of  the  cupel,  which  is  now  in- 
clined slightly  towards  the  lamp,  and  is  heated  by  the 
oxidising  flame  directed  downwards  upon  it,  this  causing 
the  globule,  when  fused  and  oxidising,  to  move  of  itself 
into  the  centre  of  the  cupel.  The  cupel  is  now  brought 
into  a  horizontal  position,  and  the  flame,  directed  on  to  it  at 
an  angle  of  about  forty-five  degrees,  is  made  to  play  upon 
the  bone-ash  surface  immediately  surrounding  the  globule, 
without,  however,  touching  it,  so  as  to  keep  this  part  of 
the  cupel  at  a  red  heat  sufficiently  strong  to  insure  the 
globule  being  in  constant  oxidising  fusion,  and  at  the  same 
time  to  cause  the  perfect  absorption  of  the  litharge,  so  as 
to  prevent  any  scales  of  litharge  forming  upon  the  surface 


FORBES'S   BLOWPIPE   ASSAY.  647 

of  the  cupel  under  the  globule,  which  would  impede  the 
oxidation,  as  well  as  prevent  the  silver  bead  being  easily 
detached  at  the  conclusion  of  the  operation.  Should  the 
heat  at  any  time  be  too  low  and  the  globule  solidify,  it 
must  be  touched  for  an  instant  with  the  point  of  the  flame 
and  proceeded  with  as  before.  Should  (in  consequence  of 
the  bone-ash  not  having  been  sufficiently  heated  to  absorb 
the  litharge  perfectly)  a  little  li tharge  adhere  pertinaciously 
to  the  globule,  or  a  particle  of  the  bone-ash  cupel  attach 
itself,  the  cupel  should  be  slightly  inclined,  so  as  to  allow 
the  globule  to  move  by  its  own  weight  on  to  another  and 
clean  part  of  the  cupel,  leaving  the  litharge  or  bone-ash 
behind  it ;  but,  if  not  sufficiently  heavy  to  do  so,  a  small 
piece  of  pure  lead  may  be  fused  to  it  in  order  to  increase 
its  weight,  and  so  allow  of  the  same  proceeding  being 
adopted. 

By  slightly  inclining  the  cupel-stand,  and  moving  it  so 
as  to  present  in  turn  all  parts  of  the  surface  surrounding 
the  globule  to  the  action  of  the  flame,  the  cupellation 
proceeds  rapidly.  If,  however,  the  assay  contains  very 
little  silver,  it  will  be  found  necessary  to  move  the  globule 
from  one  spot  to  another  on  the  cupel,  in  order  to  present 
a  fresh  surface  for  absorbing  the  litharge  formed  ;  this  is 
done  by  simply  inclining  the  cupel-stand,  remembering 
that  the  bone-ash  surrounding  the  globule  must  always  be 
kept  at  a  red  heat,  without  ever  touching  the  globule  itself 
by  the  flame. 

In  assays  rich  in  silver  a  play  of  iridescent  colours 
appears  some  seconds  before  the  '  brightening,'  which  dis- 
appears the  moment  the  silver  becomes  pure ;  as  soon  as 
this  is  observed  the  cupel  should  be  moved  in  a  circular 
manner,  so  that  the  globule  is  nearly  touched  all  round  by 
the  point  of  the  blue  flame,  and  this  is  continued  until  the 
surface  of  the  melted  silver  is  seen  to  be  quite  free  from 
any  litharge,  upon  which  it  is  very  gradually  withdrawn 
from  the  flame  so  as  to  cool  the  assay  by  degrees  very 
slowly,  in  order  to  prevent  '  spitting.' 

When  the  silver-lead  is  very  poor,  this  play  of  colours 
is  not  apparent,  and  as  soon  as  the  rotatory  movement  of 


648  THE   ASSAY    OF   SILVER. 

the  globule  ceases,  the  heat  must  be  increased  for  an  in- 
stant, in  order  to  remove  the  last  thin  but  pertinacious 
film  or  scale  of  litharge,  and  subsequently  the  assay  is 
cooled  gradually ;  when  cold  it  should,  whilst  still  upon 
the  cupel,  be  examined  by  a  lens,  to  see  whether  the 
bead  possesses  a  pure  silver  colour,  as,  if  not,  it  must  be 
reheated. 

Frequently,  when  the  '  brightening '  takes  place,  the 
silver  globule  is  found  to  spread  out,  and,  after  cooling, 
although  of  a  white  colour,  is  found  to  appear  somewhat 
less  spherical  or  more  flattened  in  shape  than  a  correspond- 
ing globule  of  pure  silver  would  be.  This  arises  from  the 
presence  of  copper  still  remaining  in  the  silver,  and  in  such 
cases  a  small  piece  of  pure  lead  (about  from  one-half  to 
one  and  a  half  grain  in  weight,  according  to  size  of  assay) 
should  be  fused  on  the  cupel  along  with  the  silver,  and  the 
cupellation  of  the  whole  conducted  as  before  on  another 
part  of  the  cupel,  when  the  silver  globule  will  be  obtained 
pure,  and  nearly  spherical  in  shape.  Sometimes  the  silver 
globule  in  '  brightening '  may  still  remain  covered  with  a 
thin  film  of  litharge,  although  otherwise  pure;  this  arises 
from  too  little  heat  having  been  employed  in  the  last  stage 
of  the  operation,  and  consequently  the  bead  should  be 
re-heated  in  a  strong  oxidising  flame  until  this  litharge 
is  absorbed,  and  the  globule,  after  slow  cooling,  appears 
pure. 

If  the  instructions  here  given  be  strictly  attended  to,  it 
will  be  found  after  some  practice  that  very  accurate  results 
may  be  obtained  in  the  blowpipe  assay  for  silver,  and  that 
no  difficulty  will  be  found  in  detecting  the  presence  and 
determining  the  amount  of  silver  present,  even  when  in  as 
small  a  quantity  as  half  an  ounce  to  the  ton.  When  sub- 
stances containing  very  little  silver  or  less  than  that  amount 
are  examined,  several  assays  should  be  made,  and  the 
silver-lead  obtained  concentrated  separately,  after  which 
the  various  globules  should  be  united  and  cupelled  together 
in  one  operation. 

It  is  hardly  necessary  to  remark  that  the  lead  employed 
in  assaying  should  be  free  from  silver,  or  if  not,  its  actual 


FORBES'S   BLOWPIPE    ASSAY.  649 

contents  in  silver  should  be  determined,  and  subtracted  from 
the  amount  found  in  the  assay. 

Assay  lead  containing  less  than  one  quarter  of  an  ounce 
to  the  ton  of  lead  can  readily  be  obtained,  or  can  be  made 
by  precipitating  a  solution  of  acetate  of  lead  by  metallic 
zinc,  rejecting  the  first  portion  of  lead  thrown  down.  In 
all  cases  the  lead  should  be  fused  and  granulated  finely — 
the  granulated  lead  for  use  in  these  assays  being  previously 
passed  through  a  sieve  containing  forty  holes  to  the  linear 
inch.  It  is  also  useful  to  have  some  lead  in  the  form  of 
wire,  as  being  very  convenient  for  adding  in  small  portions 
to  assays  when  on  the  cupel. 

Determination  of  the  Weight  of  the  Silver  Globule  ob- 
tained on  Cupellation. — As  the  amount  of  lead  which  can, 
by  the  method  before  described,  be  conveniently  cupeUed 
before  the  blowpipe  is  necessarily  limited,  the  silver  glo- 
bule which  remains  upon  the  bone-ash  surface  of  the  cupel 
at  the  end  of  the  operation  is,  when  substances  poor  in 
silver  have  been  examined,  frequently  so  very  minute  that 
its  weight  could  not  be  determined  with  correctness  by 
the  most  delicate  balances  in  general  use. 

The  blowpipe  balance  employed  by  the  author  turns 
readily  with  one-thousandth  of  a  grain,  but  could  not  be 
used  for  determining  weights  below  that  amount. 

Globules  of  silver  of  far  less  weight  than  one-thousandth 
are  distinctly  visible  to  the  naked  eye — a  circumstance 
which  induced  Harkort  to  invent  a  volumetrical  scale 
based  upon  the  measurement  of  the  diameters  of  the  glo- 
bules, which  scale  in  practice  has  been  found  of  very  great 
utility  in  the  blowpipe  assay  of  silver. 

The  scale  for  this  purpose  which  is  employed  by  the 
author  is  shown  in  full  size  in  the  annexed  woodcut. 

This  figure  represents  a  small  strip  of  highly  polished 
ivory  about  6Jt  inches  long,  §  inch  broad,  and  -^  inch  in 
thickness,  on  which  are  drawn,  by  an  extremely  fine  point, 
two  very  fine  and  distinct  lines  emanating  from  the  lower 
or  zero  point,  and  diverging  upwards  until,  at  the  distance 
of  exactly  six  English  standard  inches,  they  are  precisely 
four-hundredth  parts  of  an  inch  apart.  This  distance 


650 


THE   ASSAY   OF   SILVEE. 


FIG.  129. 


(six  inches)  is,  as  shown  in  woodcut,  divided  into  100  equal 
parts  by  cross  lines  numbered  in  accordance  from  zero 
upwards.  It  is  now  evident  if  a  small  globule 
of  silver  be  placed  in  the  space  between  these 
two  lines,  using  a  magnifying  glass  to  assist 
the  eye  in  moving  it  up  or  down  until  the 
diameter  of  the  globule  is  exactly  contained 
within  the  lines  themselves,  that  we  have  at 
once  a  means  of  estimating  the  diameter  of 
the  globule  itself,  and  therefrom  are  enabled 
to  calculate  its  weight. 

As  the  silver  globules  which  cool  upon 
the  surface  of  the  bone-ash  cupel  are  not  true 
spheres,  but  are  considerably  flattened  on  the 
lower  surface,  where  they  touch  and  rest  upon 
the  cupel,  it  follows  that  the  weight  of  glo- 
bules corresponding  in  diameter  to  the  extent 
of  divergence  at  the  different  degrees  of  the 
scale  cannot  be  calculated  directly  from  their 
diameters  as  spheres,  but  require  to  have 
their  actual  weight  experimentally  determined 
in  the  same  manner  as  employed  by  Plattner. 

The  table  here  appended  has  been  cal- 
culated by  the  author,  and  in  one  column 
shows  the  diameter  in  English  inches  corre- 
sponding to  each  number  or  degree  of  the  scale 
itself,  and  in  the  two  next  columns  the  re- 
spective weights  of  the  flattened  spheres 
which  correspond  to  each  degree  or  diameter  ; 
for  convenience  these  weights  are  given  in 
the  different  columns  in  decimals,  both  of 
English  grains  and  of  French  grammes. 

These  weights  are  calculated  from  the 
following  data,  found  as  the  average  result  of 
several  very  careful  and  closely  approximating 
assays,  which  showed  that  globules  of  silver 
exactly  corresponding  to  No.  95  on  this  scale, 
or  0-038  inch  in  diameter,  possessed  a  weight 
of  0-0475573  grains  or  0-003079  grammes.  From  this  the 


100 

98  4 

96  — 

94 

92 

90 

88  — 

-— 

86  - 

84. 

82 

80  — 

78  - 

76  ~ 

74  _I 

72  ~ 

70  _I 

66  _j; 

— 

64  _I 

62  _I 

60  JI 

58  _; 

56  — 

54  _I 

52  — 

50  ~ 

48  - 

46  ~ 

•f- 

44 

42  - 

40 

38  : 

36  - 

34  - 

30  - 

28  — 

26  - 
24  ~ 

22 

20  — 

18  - 

16  - 

14  — 

12  - 

10  — 

8~~ 

— 

6 

r~ 

4  _I 

— 



0  ~ 

FORBES  S   BLOWPIPE   ASSAY. 


651 


No.  on 
scale 

Greatest  diameter 
in  inches 

Weight  of  globule  in 
grains 

Weight  of  globule  in 
grammes 

1 

00004 

0-00000005 

0-000000003 

2 

0-0008 

0-00000044 

0-000000028 

3 

0-0012 

0-00000149 

0-000000096 

4 

0-0016 

0-00000355 

0-000000229 

5 

00020 

0-0000069 

0-00000044 

6 

0-0024 

0-0000119 

0-00000077 

7 

0-0028 

0-0000190 

0-00000120 

8 

0  0032 

0-0000284 

0-00000184 

9 

0-0036 

0-0000403 

0-00000262 

10 

0-0040 

0-0000554 

0-00000359 

11 

0-0044 

0-0000736 

0-00000478 

12 

0-0048 

0-0000958 

0-00000620 

13 

0-0052 

00001218 

0-00000789 

14 

0-0056 

0-0001522 

0-00000985 

15 

0-0060 

0-0001872 

0-00001203 

16 

00004 

0-0002272 

0-00001471 

17 

0-0068 

0-0002725 

0-00001764 

18 

0-0072 

0-0003234 

0-00002094 

19 

00076 

0-0003804 

0-00002463 

20 

0-0080 

0-0004437 

0-00002872 

21 

00084 

0-0005137 

0-00003327 

22 

0-0088 

0-0005906 

0-00003823 

23 

0-0092 

0-0006748 

0-00004367 

24 

0-0096 

0-0007668 

0-00004964 

25 

0-0100 

0-0008667 

0-00005611 

26 

0-0104 

0-0009749 

000006311 

27 

0-0108 

0-0010918 

0-00007068 

28 

0-0112 

0-0012176 

0-00007883 

29 

0-0116 

0-0013528 

0-00008758 

30 

0-0120 

0-0014976 

0-00009696 

31 

0-0124 

0-0016524 

0-00010698 

32 

00128 

0-0018176 

0-00011677 

33 

00132 

0-0019934 

0-00012817 

34 

0-0136 

0-0021801 

0-00014114 

35 

0-0140 

0-0023786 

0-00015397 

36 

0-0144 

0-0025879 

0-00016755 

37 

0-0148 

0-0028097 

0-00018190 

38 

0-0152 

0-0030437 

0-00019705 

39 

0-0156 

0-0032903 

0-00021302 

40 

0-0160 

0-0035550 

0-00022983 

41 

00164 

0-0038230 

0-00024751 

42 

0-0168 

0-0041096 

0-00026606 

43 

0-0172 

0-0044111 

0-00028553 

44 

0-0176 

0-0047250 

0-00030589 

45 

0-0180 

0-0050546 

0-00032725 

46 

0-0184 

0-0053991 

0-00034955 

47 

0-0188 

0-0057590 

0-00037285 

48 

0-0192 

0-0061344 

0-00039716 

49 

00196 

0-0065258 

0-00042250 

50 

0-0200 

0-0069335 

0-00044890 

51 

0-0204 

0-0073581 

0-00047638 

52 

0-0208 

0-0077799 

0-00050495 

53 

0-0212 

0-0082580 

0-00053464 

54 

00216 

0-00873438 

0-00056549 

55 

0-0220 

0-00922854 

0-00059748 

56 

00224 

0-0097412 

0-00063067 

652 


THE   ASSAY   OP   SILVER. 


No.  on 

scale 

Greatest  diameter 
in  inches 

Weight  of  globule  in 
grains 

Weight  of  globule  in 
grammes 

57 

0-0228 

0-0102725 

0-00066506 

58 

00232 

0-0108228 

0-00070021 

59 

00236 

0-0113922 

0-00073753 

60 

0-0240 

0-0119815   - 

000077570 

61 

0-0244 

0-0125901 

0-00081513 

62 

0-0248 

0-0132119 

0-00085588 

63 

0-0252 

0-0138901 

0-00089797 

64 

0-0256 

0-0145440 

0-00094141 

65 

0-0260 

0-0152311 

0-00098623 

66 

0-0264 

00159472 

000103245 

67 

0-0268 

0-0166828 

0-00108010 

68 

00272 

0-0174414 

0-00112918 

69 

00276 

0-0182220 

0-00117974 

70 

0-0280 

00190256 

0-00123177 

71 

00284 

00198529 

000128535 

72 

0-0288 

0-0207035 

0-00134041 

73 

0-0292 

00215782 

0-00139704 

74 

0-0296 

0-0224469 

000145525 

75 

0-0300 

0-0234010 

0-00151504 

76 

0-0304 

0-0243496 

0-00157645 

77 

00308 

0-0253224 

0-001(53950 

78 

0-0312 

0-0263228 

0-00170422 

79 

0-0316 

0-0273484 

0-00177060 

80 

0-0320 

0-0284000 

0-00183869 

81 

0-0324 

0-0294789 

0-00190852 

82 

0-0328 

0-0305838 

0-00198008 

83 

0-0332 

0-0317162 

000205340 

84 

0-0336 

0-0328768 

0-002l28ol 

85 

0-0340 

0-0340649 

0-00220549 

86 

0-0344 

0-0349739 

0  00228400 

87 

0-0348 

00364422 

000235938 

88 

0-0352 

0  0378008 

0-00244730 

89 

0-0356 

0-0390138 

000253168 

90 

0-0360 

0-0404368 

000261797 

91 

00364 

00417943 

0-00270790 

92 

0-0368 

0-0431930 

0-00279642 

93 

0-0372 

0-0446162 

0-002888(50 

94 

0-0376 

0-0460718 

0-00298279 

95 

0-0380 

0-0475573 

0-00307900 

96 

0-0384 

0  0405239 

0-00317728 

97 

0-0388 

0-0506249 

0-00327759 

98 

0-0392 

0-0522069 

0-00338020 

99 

0-0396 

0-0538215 

0-00348452 

100 

0-0400 

0-0554688 

0-00359138 

respective  weights  of  all  the  other  numbers  or  degrees  on 
this  scale  were  calculated,  on  the  principle  that  solids  were 
to  one  another  in  the  ratio  of  the  cubes  of  their  diameters. 
This  mode  of  calculation  is  not,  however,  absolutely  correct 
in  principle,  for  the  amount  of  flattening  of  the  under  sur- 
face of  the  globule  diminishes  in  reality  with  the  decreasing 


FORBES  S   BLOWPIPE   ASSAY.  653 

volume  of  the  globule.  In  actual  practice,  however,  this 
difference  may  be  assumed  to  be  so  small  that  it  may  be 
neglected  without  injury  to  the  correctness  of  the  results. 

The  smaller  the  diameter  of  the  globule,  the  less  will 
be  the  difference  or  variation  in  weight  in  descending  the 
degrees  of  this  scale,  since  the  globules  themselves  vary  in 
weight  with  the  cubes  of  their  diameters  ;  for  this  reason, 
also,  all  such  globules  as  come  within  the  scope  of  the 
balance  employed  should  be  weighed  in  preference  to  being 
measured,  and  this  scale  should  be  regarded  as  more  spe- 
cially applicable  to  the  smaller  globules  beyond  the  reach 
of  the  balance. 

Cupellation  Loss. — This  term  is  applied  to  indicate  a 
minute  loss  of  silver,  unavoidably  sustained  in  the  process 
of  cupellation,  which  arises  from  a  small  portion  of  that 
metal  being  mechanically  carried  along  with  the  litharge 
into  the  body  of  the  cupel.  The  amount  of  this  loss  in- 
creases with  the  quantity  of  lead  present "  in  the  assay 
(whether  contained  originally  in  the  assay  or  added  subse- 
quently for  the  purpose  of  slagging  off  the  copper,  &c.) ; 
it  is  relatively  greater  as  the  silver  globule  is  larger,  but 
represents  a  larger  percentage  of  the  silver  actually  con- 
tained in  the  assay,  in  proportion  as  the  silver  globule 
obtained  diminishes  in  size.  It  has,  however,  been  experi- 
mentally proved  that,  in  assays  of  like  richness  in  silver, 
this  loss  remains  constant  when  the  same  temperature  has 
been  employed,  and  similar  weights  of  lead  have  been 
oxidised  in  the  operation. 

In  the  blowpipe  assay  this  loss  is  not  confined  to  the 
ultimate  operation  of  cupellation,  but  occurs,  though  in  a 
less  degree,  in  the  concentration  of  the  silver -lead,  and  in 
the  previous  scorification  of  the  assay,  had  such  operation 
preceded  the  concentration.  The  total  loss  in  the  blow- 
pipe assay  is  found,  however,  to  be  less  than  in  the  ordinary 
muffle  assay,  since  in  the  latter  case  the  whole  of  the  oxi- 
dised lead  is  directly  absorbed  by  the  cupel. 

In  mercantile  assays  of  ore  it  is  not  customary  to  pay 
attention  to  the  cupellation  loss,  and  the  results  are  usually 
stated  in  the  weight  of  silver  actually  obtained.  Where, 


654 


THE   ASSAY   OF   SILVER. 


however,  great  accuracy  is  required,  especially  when  the 
substances  are  very  rich  in  silver,  the  cupellation  loss  is 
added  to  the  weight  of  the  silver  globule  obtained,  in  order 
to  arrive  at  the  true  percentage. 

The  amount  to  be  added  for  this  purpose  is  shown 
in  the  annexed  table,  which  is  slightly  modified  from 
Plattner's : — 


Actual  per- 
centage  of 
silver  found  by 
assay 

Cupellation   loss,  or  percentage   of  silver  to   be  added  to  the  actual   percentage 
found  by  assay  in  order  to  show  the  true  percentage  of  silver  contained  in  same. 
The  entire  amount  of  lead  in  or  added  to  the  assay  being  the  following  multiples 
of  the  original  weight  of  assay  :  — 

1 

2 

3 

4 

5 

6 

8 

11     |    13 

16 

9975  ) 
99-5    [ 

0-25 

0-32 

0-39 

0-45 

0-50 

90 

0-22 

0-29 

0-36 

042 

0-47 

069 

0-83 

80 

0-20 

0-26 

0-33 

0-39 

0-44 

0-64 

075 

70 

0-18 

0-23 

0-29 

0-35 

0-40 

0-58 

0-68 

0-82 

60 

0-16 

0-20 

0-26 

0-30 

0-36 

0-52 

0-61 

0-74 

50 

0-14 

0-17 

0-23 

0-26 

0-32 

0-46 

0-54 

0-65 

40 

0-12 

0-15 

0-20 

0-22 

0-27 

0-39 

0-46 

0-55 

0-62 

35 

0-11 

0-13 

0-18 

0-18 

0-25 

0-36 

0-42 

050 

0-57 

30 

0-10 

0-12 

0-16 

0-16 

0-22 

0-32 

0-38 

0-45 

0-51 

25 

0-09 

0-10 

0-14 

0-14 

0-20 

029 

0-34 

0-40 

0-45 

20 

0-08 

0-09 

0-12 

0-12 

0-17 

0-25 

0-29 

0-35 

0-39 

0-45 

15 

0-07 

0-08 

0-10 

0-11 

0-15 

0-20 

023 

0-28 

0-32 

0-37 

12 

006 

0-07 

0-09 

0-10 

0-13 

0-17 

0-19 

0-23 

026 

0-22 

10 

0-05 

0-06 

008 

0-09 

0-11 

0-15 

0-17 

0-20 

0-23 

0-27 

9 

0-04 

0-05 

0-07 

0-08 

0-10 

0-14 

0-16 

0-18 

0-21 

0-25 

8 

0-03 

0-04 

0-06 

0-07 

0-09 

0-13 

0-15 

0-16 

0-18 

0-22 

7 

0-02 

0-03 

005 

0-06 

0-08 

0-12 

0-13 

0-14 

0-16 

0-20 

6 

o-oi 

0-02 

0-04 

0-05 

0-07 

0-10 

0-11 

0-12 

0-14 

0-17 

5 

o-oi 

0-03 

004 

0-06 

0-09 

0-10 

0-11 

0-12 

0-14 

4 

0-02 

0-03 

0-05 

0-07 

0-08 

0-09 

0-10 

0-11 

3 

o-oi 

0-02 

0-04 

0-05 

0-06 

0-07 

0-08 

0-09 

2 

o-oi 

003 

0-04 

004 

0-05 

0-06 

0-07 

1 

001 

0-03 

0-03 

0-04 

004 

0-05 

The  use  of  this  table  is  best  explained  by  an  example, 
as  the  following  : — An  assay  to  which  there  had  been 
added,  in  all,  five  times  its  weight  of  assay  lead,  gave  a 
globule  of  silver  equivalent  to  six  per  cent.  Upon  referring 
to  the  table  it  will  be  seen  that  the  cupellation  loss  for  this 
would  be  0-07  ;  consequently  the  true  percentage  of  silver 
contained  in  the  assay  would  be  6 -07.  This  table  is  only 
extended  to  whole  numbers,  but  fractional  parts  can  easily 
be  calculated  from  the  same. 


FORBES  S   BLOWPIPE   ASSAY.  655 

When  the  globules  of  silver  are  so  minute  that  they 
cannot  be  weighed,  but  must  be  measured  upon  the  scale, 
the  cupellation  loss  should  not  be  added,  since,  as  a  rule, 
it  would  be  less  than  the  difference  which  might  arise  from 
errors  of  observation  likely  to  occur  when  measuring  their 
diameters  upon  the  scale. 

In  the  case  of  beginners,  it  will  be  found  that  the  cupel- 
lation is  usually  carried  on  at  too  high  a  temperature,  and 
that  thereby  a  greater  loss  is  occasioned  than  would  be 
accounted  for  by  the  above  table.  After  some  trials  the 
necessary  experience  will  be  acquired  in  keeping  up  the 
proper  temperature  at  which  this  operation  should  be 
effected. 

It  now  becomes  necessary  to  consider  in  detail  the 
processes  requisite  for  extracting  the  silver  contents  (in 
combination  with  lead)  from  the  various  metallic  alloys  of 
silver  which  are  met  with  in  nature  or  produced  in  the 
arts. 

In  considering  these,  the  following  classification  of  the 
substances  will  be  found  convenient : — 

METALLIC  ALLOTS. 

A.  Capable  of  direct  Cupellation. 

a.  Consisting  chiefly  of  lead  or  bismuth  ;  silver-lead  and  argen- 

tiferous bismuth,  native  bismuthic  silver. 

b.  Consisting  chiefly  of  silver:  native  silver,  bar  silver,  test 

silver,  precipitated  silver,  retorted  silver  amalgam,  stan- 
dard silver,  alloys  of  silver  with  gold  and  copper. 

c.  Consisting  chiefly  of  copper:  native  copper,  copper  ingot, 

sheet  or  wire,  cement  copper,  copper  coins,  copper-nickel 
alloys. 

£.  Incapable  of  direct  Cupellation. 

a.  Containing  much  copper  or  nickel,  with  more  or  less  sulphur, 

arsenic,  zinc,  &c. ;  unrefined  or  black  copper,  brass,  Ger- 
man silver. 

b.  Containing  tin  ;  argentiferous  tin,  bronze,  bell-metal,  gun- 

metal,  bronze  coinage. 

c.  Containing  antimony,  tellurium,  or  zinc. 

d.  Containing  mercury  :  amalgams. 

e.  Containing  much  iron :  argentiferous  steel,  bears  from  smelt- 

ing furnaces. 


656  THE   ASSAY   OF   SILVER. 


A.  METALLIC  ALLOYS  CAPABLE  OF  DIRECT  CUPELLATION. 

a.  Consisting  chiefly  of  Lead  or  Bismuth. — In  determin- 
ing the  silver  contained  in  these  alloys,  it  is  only  requisite 
to  place  a  clean  piece  of  the  same,  weighing  about  from 
one  to  ten  grains  according  to  its  probable  richness  in 
silver,  upon  a  cupel  of  coarse  bone-ash,  and  proceed  by 
concentration  and  cupellation  exactly  as  has  been  already 
described  under  these  heads. 

Should  the  substance  be  not  altogether  metallic,  or  not 
free  from  adherent  slag,  earthy  matter,  or  other  extraneous 
matter,  it  should  previously  be  fused  on  charcoal  with  a 
little  borax  in  the  reducing  blowpipe  flame,  and  the  clean 
metallic  globule  then  removed  from  the  charcoal,  and 
treated  as  before.  In  order  to  remove  the  globule  from 
the  adherent  borax-glass,  it  may  be  allowed  to  cool,  and 
then  detached ;  or,  after  a  little  practice,  it  will  be  found 
easy,  by  a  quick  movement  of  the  charcoal,  to  cause  the 
globule,  still  melted,  to  detach  itself  completely,  and  drop 
on  the  anvil  in  the  form  of  a  single  somewhat  flattened 
globule,  without  suffering  any  loss  of  lead  adhering  to  the 
charcoal. 

In  the  case  of  argentiferous  bismuth  alloys  the  process 
is  carried  on  in  all  respects  the  same  as  if  silver-lead  were 
being  treated.  As,  however,  the  bismuth  globule  is  very 
brittle,  care  must  be  taken  when  separating  the  concen- 
trated globule  from  the  litharge,  as,  if  not  carefully  done, 
a  loss  may  easily  be  sustained  from  a  portion  of  the  glo- 
bule remaining  behind  adherent  to  the  litharge.  It  is 
better,  therefore,  to  remove  the  litharge  by  degrees  from 
the  globule  with  the  aid  of  the  forceps. 

Argentiferous  bismuth,  free  from  lead,  when  cupelled 
alone,  invariably  leaves  a  globule  of  silver,  having  a  dull 
frosted  surface.  If,  however,  at  the  end  of  the  operation 
a  small  quantity  of  lead  (i  to  ±  a  grain)  be  added,  and 
fused  along  with  it,  the  silver  globule  then  obtained  will 
"be  perfectly  bright  and  free  from  all  bismuth. 

In  the  case  of  native  bismuthic  silver  it  is  advisable  to 


FOKBES'S   BLOWPIPE   ASSAY.  657 

fuse  the  previously  weighed  mineral  with  a  little  lead  and 
borax-glass  on  charcoal  in  the  reducing  flame,  so  as  to 
free  it  from  any  adherent  earthy  matter,  and  then  proceed 
by  concentration  and  cupellation,  as  before  described. 

b.  Consisting  chiefly  of  Silver :  native  silver,  bar,  test, 
and  precipitated  silver,  retorted  silver  amalgam,  standard 
silver,  silver  coin  and  other  alloys  of  silver  with  gold  and 
copper. — These  alloys  may  be  at  once  fused  with  lead  on 
the  cupel  itself,  and  the  operation  finished  as  before  de- 
scribed. In  general,  however,  it  is  better  to  fuse  the 
weighed  assay  previously  with  the  requisite  amount  of 
pure  lead  and  a  little  borax-glass,  say  from  a  quarter  to 
half  the  weight  of  assay,  in  the  reducing  flame  at  a  low 
heat  on  charcoal  until  the  globule  commences  to  rotate. 
This  ensures  having  a  perfectly  clean  button  of  silver- 
lead,  which  is  then  cupelled  in  the  ordinary  manner. 

In  most  cases  the  quantity  of  lead  to  be  added  need 
not  exceed  that  of  the  weight  of  the  alloy,  but  when 
several  percentages  of  copper  are  present  in  the  assay,  as 
in  the  case  of  many  coins,  &c.,  the  lead  should  be  increased 
to  some  three,  or  even  five,  times  the  weight  of  the  assay 
in  proportion  to  the  amount  of  copper  actually  contained 
in  the  substance  under  examination,  and  which  will  be 
treated  of  more  at  length  under  the  head  of  copper-silver 
alloys. 

When  no  more  lead  has  been  added  to  the  assay  than 
its  own  weight,  the  cupellation  may  be  concluded  in  one 
operation  by  inclining  the  stand,  and  so  moving  the  glo- 
bule to  a  clean  part  of  the  cupel ;  but  when  more  copper 
is  present,  it  is  preferable  to  concentrate  first  and  cupel 
subsequently,  in  order  thereby  to  reduce  the  cupellation 
loss  to  its  minimum. 

In  the  concentration  as  much  copper  as  possible  should 
be  slagged  off  with  the  lead,  which  is  effected  by  inclining 
the  cupel  somewhat  more  than  usual,  so  that  its  surface 
may  be  less  covered  up  with  the  litharge  and  exposed  as 
much  as  possible  to  oxidation,  by  which  means  the  litharge, 
as  it  forms,  is  enabled  to  carry  off  more  of  the  copper  con- 
tained in  the  silver-lead. 

u  u 


658  THE   ASSAY   OF   SILVER. 

Should  the  silver  globule  after  cupellation  show  indi- 
cations of  still  containing  copper,  as  before  noticed,  when 
treating  of  cupellation,  a  small  quantity  of  lead  must  be 
fused  along  with  it,  and  the  cupellation  finished  as  usual. 

As  at  the  present  time  no  means  are  known  by  which 
silver  can  be  separated  from  gold  by  the  use  of  the  blow- 
pipe in  all  cases  of  alloys  containing  gold,  this  metal 
remains  to  the  last  along  with  the  silver,  and  the  result  in 
such  cases  always  indicates  the  combined  weight  of  both 
these  metals  contained  in  the  alloy  under  examination. 
The  wet  assay  must  be  resorted  to  for  effecting  their 
separation. 

c.  Containing  chiefly  Copper :  native  copper,  ingot,  wire 
or  sheet  copper,  cement  copper,  copper  coins,  copper-nickel 
alloys. — Under  the  most  favourable  conditions  in  cupella- 
tion, the  amount  of  lead  requisite,  when  converted  into 
litharge,  to  slag  off  one  part  of  copper  along  with  it  as 
oxide,  amounts  to  between  seventeen  and  eighteen  times 
its  weight.  In  the  blowpipe  assay  it  is  usual  to  add  to 
any  cupriferous  alloy  an  amount  of  pure  lead  equal  to 
twenty  times  the  amount  of  copper  contained  in  the  alloy, 
in  order  to  ensure  the  whole  of  the  copper  being  separated 
in  the  litharge.  In  the  case  of  nickel  the  amount  of  lead 
required  is  somewhat  less  than  with  copper,  but  in  prac- 
tice the  same  amount  of  lead  may  be  employed. 

When  the  copper  is  quite  clean  the  requisite  amount 
of  lead  may  be  added  to  it  in  a  single  piece  on  the  cupel, 
fused  and  cupelled  as  usual,  after  previous  concentration 
of  the  silver-lead  to  a  small-sized  globule. 

It  is  generally  found,  however,  that  traces  of  iron,  slag, 
gangue,  or  other  foreign  matter,  are  present ;  and,  conse- 
quently, it  is  usually  advisable  to  fuse  the  assay  along 
with  the  requisite  amount  of  lead,  and  about  one-half  its 
own  weight  of  borax-glass  in  the  reducing  flame,  until  the 
whole  of  the  substance  is  seen  to  have  perfectly  combined 
or  alloyed  with  the  lead,  and  the  globule  has  entered  into 
brisk  rotation,  whilst  at  the  same  time  no  detached 
metallic  globules  are  seen  in  the  borax-glass. 

The  concentration  of  the  silver-lead  and  cupellation 


FORBES  S   BLOWPIPE   ASSAY.  659 

are  then  conducted  as  usual,  taking  care  when  concentra- 
ting to  incline  the  cupel-stand  so  as  to  expose  as  much  as 
possible  of  the  metallic  surface  of  the  melted  globule  to 
the  oxidising  action  of  the  air,  with  a  view  of  enabling  the 
litharge  whilst  forming  to  carry  off  as  much  copper  along 
with  it  as  possible. 

Should  the  silver  globule  obtained  after  cupellation 
spread  out,  or  appear  to  the  eye  more  flattened  than 
usual  with  globules  of  pure  silver,  it  indicates  that  some 
copper  still  remains,  and  a  small  piece  of  assay  lead  (^  to 
1  grain  weight)  should  be  placed  alongside  it  whilst  still 
on  the  cupel,  fused  together,  and  the  cupellation  finished 
on  a  clean  part  of  the  same  cupel  as  usual. 

Precipitated  or  cement  copper,  especially  that  which 
is  in  the  crude  state,  and  has  not  been  melted  and  run 
into  ingots,  is  often  very  impure,  containing  so  much  iron, 
lead,  arsenic,  earthy  matter,  &c.,  as  not  to  admit  of  direct 
cupellation,  and  in  such  case  should  be  treated  as  pertain- 
ing to  class  B.  #. 

B.  METALLIC  ALLOYS  INCAPABLE  OF  DIRECT  CUPELLATIOX. 

a.  Containing  much  Copper  or  Nickel,  with  frequently 
some  little  sulphur,  arsenic,  zinc,  iron,  cobalt,  fyc.,  as  unre- 
fined or  black  copper,  brass,  German  silver,  fyc. — As  the 
presence  of  these  extraneous  matters  would  interfere  with 
the  cupellation,  either  by  causing  a  loss  of  silver-lead 
projected  from  the  cupel  upon  the  evolution  of  the 
volatile  substances  present,  or  by  forming  oxides  which 
could  not  be  absorbed  by  the  cupel,  it  is  necessary  to 
eliminate  such  substances  by  a  scorification  with  borax  on 
charcoal,  previous  to  concentration  or  cupellation. 

In  the  case  of  unrefined  and  black  copper,  the  portion 
used  in  the  examination  is  placed  in  the  scoop  with  twenty 
times  its  weight  of  assay  lead,  and  its  own  weight  of  pow- 
dered borax-glass,  mixed  with  the  spatula,  and  transferred 
to  a  soda-paper  cornet.  It  is  then  fused  on  charcoal  in 
the  reducing  flame,  which  should  be  constant  and  uninter- 
rupted, until  all  particles  have  completely  united,  and  a 


660  THE   ASSAY   OF   SILVER. 

brisk  rotation  sets  in,  which  is  kept  up  for  a  short  time, 
when  the  silver-lead  globule,  which  should  appear  bright 
on  the  surface  after  cooling,  is  concentrated  and  cupelled 
precisely  as  is  directed  under  A.  c.  By  this  preliminary 
scorification  the  sulphur,  arsenic,  and  zinc  are  volatilised, 
and  any  lead,  cobalt,  or  iron  slagged  off  into  the  borax- 
gjass. 

In  the  assay  of  brass  and  German  silver,  the  quantity 
Employed  is  fluxed  with  its  own  weight  of  borax-glass,  but 
only  requires  ten  times  its  weight  of  assay-lead.  The 
operation  is  commenced  as  before,  but  the  globule  is  kept 
somewhat  longer  in  rotation  (always  keeping  the  flame 
directed  only  on  to  the  borax  glass),  so  as  to  allow  the  zinc 
present  to  be  completely  volatilised,  which  is  evident  when 
the  surface  of  the  silver-lead  becomes  bright,  on  which  the 
heat  is  increased  for  a  few  moments  to  expel  the  last  traces 
of  that  metal,  and  the  silver  lead  thus  obtained  is  concen- 
trated and  cupelled  as  before. 

The  silver  globule  obtained  from  the  cupellation  of 
substances  rich  in  copper  generally  requires  the  addition 
of  a  small  quantity  of  lead  and  re-cupellation  (as  before 
described),  in  order  to  insure  its  freedom  from  copper. 

b.  Containing  Tin:  argentiferous  tin,  bronze,  bell  and 
gun  metal,  bronze  coinage,  fyc. — Alloys  of  silver  with  other 
metals  containing  tin  do  not  admit  of  being  cupelled,  since 
the  oxide  of  tin  formed  by  the  oxidation  of  that  metal  is 
not  absorbed  by  the  bone  ash  of  the  cupel  along  with  the 
litharge ;  it  consequently  remains  upon  the  surface  of  the 
cupel,  and  if  present  in  any  quantity  interferes  with  the 
operation.  As  tin  is  not  volatile  when  heated  on  charcoal 
either  in  the  oxidising  or  reducing  blowpipe  flame,  it 
cannot  be  so  dissipated,  and,  in  consequence,  the  entire 
amount  of  tin  contained  in  any  alloy  under  examination^ 
must  be  removed  by  oxidation  or  scorification  from  the 
silver-lead,  previous  to  its  being  submitted  to  cupellation. 

For  this  purpose,  1  part  of  the  stanniferous  alloy  is 
fluxed  with  from  5  to  15  parts  of  granulated  assay  lead  (ac- 
cording to  the  amount  of  copper  suspected  to  be  present  in 
the  alloy),  0'5  part  anhydrous  sodium  carbonate,  and  0*5 


FORBES  S   BLOWPIPE   ASSAY.  661 

part  pulverised  borax-glass,  made  up  as  usual  in  a  soda- 
paper  cornet,  and  the  whole  at  first  gently  heated  in  the 
reducing  flame  until  the  soda-paper  is  charred  and  the 
alloy  has  afterwards  united  with  the  lead  to  form  a  single 
globule,  whilst  the  borax  and  soda  have  combined  as  a 
glass  or  slag  in  which  the  soda  prevents  the  easily  oxidis- 
able  tin  becoming  oxidised  to  any  extent  before  a  perfect 
alloy  has  been  formed  with  the  lead,  which  then  contains 
the  whole  of  the  silver. 

As  soon  as  this  is  effected,  the  blowpipe  flame  is  altered 
to  an  oxidising  one,  and  the  metallic  globule  is  kept  at 
the  point  of  the  blue  flame,  which  should  touch  it  so  as  to 
cause  the  tin  to  become  oxidised  and  be  at  once  taken  up 
by  the  glass  surrounding  it. 

Should,  however,  it  be  seen  that  minute  globules  of 
metallic  tin  made  their  appearance  on  the  outer  edge  of 
the  slag  or  glass,*  the  operation  must  be  at  once  discon- 
.  tinued,  and  the  assay  allowed  to  cool ;  after  cooling  the 
metallic  globule  is  detached  from  the  slag  surrounding  it, 
and  being  placed  in  a  cavity  on  charcoal,  is  fused  in  the 
reducing  flame  along  with  a  small  piece  of  borax-glass 
and  afterwards  treated  with  the  oxidising  flame  exactly  as 
before  (and  if  necessary,  which  is  seldom  the  case,  unless 
when  treating  argentiferous  block-tin,  this  operation  may 
again  require  to  be  repeated),  until  it  is  seen  that  the 
surface  of  the  metallic  silver-lead  globule  does  not  any 
longer  become  covered  with  a  crust  or  scales  of  tin  oxide, 
but  presents  a  pure  and  bright  metallic  surface. 

The  silver-lead  globule  is  now  quite  free  from  tin,  and 
can  be  cupelled  and  the  amount  of  silver  determined  as 
usual. 

c.  Metallic  alloys  containing  much  antimony,  tellurium, 
or  zinc :  antimonial  silver  and  argentiferous  antimony,  tel- 
luric silver,  and  argentiferous  zinc. — Alloys  of  antimony 
with  silver  when  treated  on  charcoal  in  the  oxidising 
flame  give  off  all  their  antimony,  leaving  the  silver  behind 
as  a  metallic  globule  having  a  frosted  external  appearance  ; 

*  This  occurs  when  the  flux  has  become  so  saturated  with  tin  oxide  that  it 
cannot  take  up  any  more. 


662  THE   ASSAY   OF   SILVER. 

telluric  silver,  on  the  contrary,  however,  when  treated 
in  a  similar  manner,  only  evolves  a  part  of  its  tellurium, 
and  even  after  cupellation  with  lead  a  small  amount 
of  tellurium  generally  remains  behind  alloyed  with  the 
silver. 

All  these  compounds  may  be  assayed  as  follows  : — 
One  part  of  the  alloy  is  placed  in  a  soda-paper  cornet 
along  with  5  parts  of  granulated  assay  lead,  and  0'5  part 
of  pulverised  borax-glass,  and  fused  in  the  reducing  flame 
until  the  globule  and  s]ag  are  well  developed ;  the  oxidising 
flame  is  now  directed  on  to  the  globule,  causing  the 
whole  of  the  zinc,  along  with  most  of  the  antimony  and 
part  of  the  tellurium,  to  volatilise  before  the  lead  com- 
mences oxidising.  The  last  traces  of  antimony  are  re- 
moved with  some  difficulty,  during  which  operation  some 
portion  of  the  lead  becomes  oxidised.  On  cooling,  the 
globule  is  separated  from  the  slag  and  concentrated  upon 
a  coarse  bone-ash  cupel  as  usual,  and  if  no  tellurium  were 
present  in  the  concentrated  silver-lead,  this  may  now  be 
cupelled  as  usual. 

If  tellurium  is  present — as  is  seen  by  the  concentrated 
globule  of  silver-lead  possessing  a  dark-coloured  exterior 
— it  must  be  remelted  with  5  parts  of  assay  lead  and  again 
concentrated  ;  and  these  operations,  if  necessary,  must  be 
repeated  until  the  surface  of  the  concentrated  globule  is 
found  to  be  clean  and  bright,  as  is  usual  with  pure  silver- 
lead,  when  it  may  be  cupelled  fine  and  the  silver  globule 
weighed. 

It  sometimes  happens,  even  after  all  these  precautions 
have  been  taken,  that  the  silver  globule  after  cupellation 
shows  a  crystalline,  greyish-white,  frosted  appearance,  from 
its  still  containing  tellurium  ;  in  such  cases  its  own  weight 
of  assay  lead  (in  one  piece)  should  be  placed  beside  it  on 
the  cupel,  melted  together,  and  the  globule  again  cupelled 
fine  on  another  part  of  the  surface  of  the  same  cupel.  In 
assaying  substances  very  rich  in  tellurium  the  results  ob- 
tained are,  however,  not  very  satisfactory,  and  may  be  as 
much  as  one  or  two  per  cent,  too  low,  even  after  employ- 
ing all  precautions. 


FORBES'S   BLOWPIPE  ASSAY.  663 

d.  Compounds  of  Silver  with  Mercury :  arquerite,  native 
and  artificial  amalgams  and  argentiferous  mercury. — The 
assay   of  these  compounds  is  very  simple.     A  weighed 
quantity  of  the  liquid  or  solid  amalgam  is  placed  in  a  small 
bulb-tube,  and  heated  over  the  lamp  very  gradually  in 
order  to  avoid  spirting  and  to  allow  the  mercury  to  volati- 
lise quietly  ;  *  the  heat  is  increased  by  degrees  as  long  as 
any  mercury  is  driven  off,  and  the  residue  is  heated  for 
some  time  at  a  red  heat  in  order  to  drive  off  as  much  mer- 
cury as  possible  without  fusing  the  glass  or  causing  the 
residual  silver  to  adhere  to  it.     The  mercury  expelled  con- 
denses itself  above  the  bulb  on  to  the  upper  part  of  the 
tube,  and  by  gently  tapping  will  collect  in  globules,  which 
by  carefully  turning  the  tube,  unite  and  can  be  poured 
out  of  the  tube ;  after  which  the  silver,  left  behind  as  a 
porous  mass,  may  be  removed  from  the  tube,  and  after 
being  fluxed  with  an  equal  weight  of  granulated  assay 
lead  and  half  its  weight  of  borax-glass,  must  be  fused  on 
charcoal  in  the  reducing  flame,  and  the  button,  on  cooling, 
cupelled  as  usual.     Should,  however,  much  copper  have 
been  present  in  the  amalgam,  a   proportionately   larger 
amount  of  assay  lead  is  required  to  be  added. 

When  the  argentiferous  residue  is  extremely  small,  as 
is  often  the  case  when  assaying  argentiferous  mercury, 
this  may  adhere  firmly  to  the  glass  of  the  tube.  On  such 
occasions  this  part  of  the  tube  must  be  cut  off  with  the 
adherent  residue,  and  the  whole  fused  in  a  strong  reducing 
flame  along  with  its  own  weight  of  granulated  assay  lead, 
and  with  half  its  weight  of  anhydrous  sodium  carbonate. 
Upon  cooling,  the  globule  of  silver-lead  thus  obtained  is 
cupelled  as  usual. 

e.  Compounds  chiefly  consisting  of  Iron :  argentiferous- 
steel;  cast-iron;  bears  from  smelting  furnaces. — Compounds 
consisting  principally  of  iron  with  a  small  percentage  of 
silver,  although  occasionally  produced  in  the  arts  inten- 
tionally, as,  for  example,  the  so-called  silver-steel,  are  corn- 

*  In  the  case  of  solid  amalgams,  which  often  spirt  very  violently,  this  may 
be  obviated  by  wrapping  the  assay  in  a  small  piece  of  tissue  paper,  and  heating 
it  in  a  blowpipe  crucible,  when  all  the  mercury  is  given  off  quietly,  leaving  the 
silver  behind. 


664  THE   ASSAY    OF   SILYEE. 

monly  found  on  the  blowing-out  of  furnaces  used  in  the 
smelting  of  silver  and  copper  ores,  and  are  frequently  rich 
in  silver,  as  is  the  case  with  the  bears  from  the  silver  fur- 
naces at  Kongsberg  in  Norway.  An  alloy  of  iron  with 
silver  is  occasionally  also  found  appearing  in  small  quanti- 
ties on  the  surface  of  melted  silver  in  the  process  of  cast- 
ing, and  in  some  cases  at  least  this  may  be  due  to  the  action 
of  the  melted  silver  on  the  iron  rods  used  for  stirring  up 
the  molten  metal. 

As  iron  cannot  be  made  to  alloy  itself  with  lead  before 
the  blowpipe,  it  becomes  necessary  to  extract  the  silver  by 
a  more  indirect  process  than  is  used  in  the  case  of  other 
alloys  containing  that  metal.  In  order  to  remove  the  iron 
the  alloy  must  first  be  converted  into  iron  and  silver  sul- 
phide, and  to  effect  this  'the  iron  or  steel  must  be  reduced 
to  powder,  or  fragments  none  greater  than  about  a  quarter 
of  a  grain  in  weight ;  for  which  purpose  steel  when  har- 
dened may  require  to  be  softened  previously. 

One  part  of  the  finely-divided  iron  or  steel  is  now  mixed 
with  0*75  part  sulphur,  eight  parts  granulated  assay  lead, 
and  one  part  pulverised  borax-glass :  the  mixture  after 
being  placed  in  a  soda-paper  cornet  is  carefully  fused  in  a 
cavity  on  charcoal  in  the  reducing  flame,  until  the  whole 
appears  as  a  fluid  globule  containing  both  the  lead  and 
iron  in  combination  with  the  sulphur.  Without  removing 
either  this  globule  or  the  glass  surrounding  it  from  the 
charcoal,  an  amount  of  borax-glass  in  one  or  more  frag- 
ments (in  all  about  equal  in  weight  to  the  original  amount 
of  iron  employed),  is  now  added  (in  order  to  combine  with 
and  slag  off  the  whole  of  the  iron),  and  fused  along  with  the 
former  globule,  after  which  the  whole  is  submitted  to  a 
strong  oxidising  flame  until  the  impure  lead  globule  shows 
itself  protruding  from  the  slag. 

The  charcoal  is  then  inclined,  so  that  the  lead  is  alone 
subjected  to  the  action  of  the  outer  flame,  in  order  to  vola- 
tilise the  sulphur,  and  at  the  same  time  oxidise  the  iron 
which  goes  into  the  slag ;  this  operation  is  continued  until 
the  globule  of  lead  appears  with  a  bright  metallic  surface  ; 
should  it  on  cooling,  however,  be  found  to  possess  a  black 


ASSAY   OF   ALLOYS   OF   SILVER   AXD    COPPER,  665 

colour,  and  to  be  brittle,  if  must  be  still  further  oxidised  as 
before  described. 

The  silver-lead  thus  obtained  will  now  be  found  to 
contain  all  the  silver,  and  at  the  same  time  to  be  free  from 
both  iron  and  sulphur,  and  can  be  cupelled  as  usual. 

No  notice  is  here  taken  of  alloys  of  silver  and  gold, 
since  these  metals  cannot  be  separated  before  the  blowpipe 
by  any  process  yet  known  ;  and  in  all  cases  where  gold 
may  be  present  in  an  alloy,  treated  as  here  directed  for 
obtaining  its  contents  in  silver,  the  gold  also  will  be  found 
to  follow  along  with  the  silver,  and  must  be  parted  from 
that  metal  by  the  wet  method,  in  order  to  enable  the 
true  amount  of  silver  present  in  the  substance  to  be  ascer- 
tained. 

Alloys  of  Silver  and  Copper. — A  quantity  of  from  1 
to  2  grms.  is  placed  in  a  small  flask  or  beaker,  treated 
with  a  sufficient  quantity  of  pure  nitric  acid  of  a  moderate 
strength,  covered  with  a  watch-glass  and  digested  at  a 
gentle  heat  till  totally  dissolved.  The  solution  is  then 
diluted  with  water,  and  the  silver  precipitated  with  hydro- 
chloric acid,  which  is  added  drop  by  drop  as  long  as  any- 
thing is  thrown  down.  It  is  then  allowed  to  digest  at  a 
very  gentle  heat  till  the  supernatant  liquid  is  clear.  The 
liquid  is  then  poured  upon  a  dried  and  counterpoised  filter  ; 
the  silver  chloride  is  stirred  up  with  a  little  water,  and 
brought  upon  the  filter,  the  glass  being  perfectly  rinsed  out 
by  aid  of  the  washing-bottle.  A  few  drops  of  nitric  acid 
may  be  usefully  added  to  the  rinsing-water.  The  washing 
is  afterwards  continued  with  pure  water  till  the  droppings 
have  no  longer  an  acid  reaction.  The  filter  with  its  con- 
tents is  dried,  and  from  its  weight  that  of  the  silver  is 
calculated. 


CHAPTER  XVII. 

THE    ASSAY    OF     GOLD. 

FOR  the  purposes  of  assay,  all  substances  containing  gold 
may  be  divided  into  two  classes,  as  in  the  case  of  silver. 

The  First  Class  comprises  ores  containing  gold  in  a 
mineralised  form. 

The  Second  Class  comprises  all  alloys  of  gold,  native  or 
artificial. 

CLASS  I. — Minerals. 

Graphic  Tellurium,  (AuAg)  Te3,  containing  30  per  cent, 
of  gold,  and  10  per  cent,  of  silver. 

Folliated  Tellurium,  (Pb,Au,Ag)2  (Te,Sb,S)3  containing 
about  9  per  cent,  of  gold. 

CLASS  II. — Alloys  of  Gold. 

Native  Gold,  AuAg,  containing  65-99  per  cent,  of 
gold. 

Palladium  Gold,  AuPd,  containing  about  86  per  cent, 
of  gold. 

Rhodium  Gold,  AuEh,  containing  59-66  per  cent,  of 
gold. 

Gold  Amalgam,  (Au,Ag)2  Hg5,  containing  38  per  cent, 
of  gold. 

Artificial  Alloys,  Gold  coin,  jewellery,  &c. 

Of  the  foregoing  list,  native  gold  alone  occurs  in  nature 
in  sufficient  abundance  to  acquire  any  great  commercial 
value.  It  is  commonly  found  in  a  quartzose  gangue,  and 
nearly  always  associated  with  one,  or  more,  of  the  following 


NATIVE   GOLD.  667 

minerals  :  iron  and  copper  pyrites,  mispickel  or  arsenical 
pyrites,  blende,  galena,  many  antimonial  minerals,  and 
nearly  all  the  primitive  rocks.  All  auriferous  slags,  amal- 
gamation residues  and  tailings,  belong  to  this  class. 

If  silver  or  platinum  are  associated  with  the  gold  in  the 
mineral  subjected  to  assay,  it  will  be  found  combined  with 
the  gold  obtained  by  cupejlation  ;  and  all  gold  so  obtained 
must  be  submitted  to  the  '  parting  process,'  which  see 
further  on. 

When  gold  is  associated  in  quantity  with  quartz,  its 
percentage  can  be  approximatively  ascertained  in  the  same 
manner  as  that  of  pure  tin-stone  when  mixed  with  quartz 
(see  page  486).  If  possible,  a  fragment  of  the  gold  must 
be  detached  from  the  quartz,  and  its  specific  gravity 
taken  :  if  this  be  not  possible,  and  the  gold  is  nearly 
fine,  the  number  19  may  be  adopted.  It  is  better,  how- 
ever, to  determine  experimentally  the  specific  gravity  of 
both  quartz  and  gold. 

Native  Gold  and  Aurides  of  Silver  (Native)  are 
found  in  variously  contorted  and  branched  filaments,  in 
scales,  in  plates,  in  small  irregular  masses,  in  the  crevices 
or  on  the  surface  of  common  ferruginous  and  other 
quartz. 

The  author  has  received  two  specimens  of  gold,  one 
from  Wales,  and  the  other  from  the  Britannia  Mine,  Devon  ; 
and  found  both  to  be  absolutely  fine  gold. 

Artificial  Alloys  of  Gold. — The  only  one  of  these  alloys 
which  will  be  specially  noticed  here,  is  the  standard  gold 
of  this  realm.  It  is  composed  of  22  parts  of  fine  gold  and 
2  parts  of  alloy,  constituting  22-carat  or  standard  gold. 

ASSAY   OF   GOLD   ORES.* 

The  assay  of  gold  ores  embrace  the  following  steps  : — 

1.  Preparation  of  the  sample.     2.  Collection  of  the 

gold  in  a  button  of  metallic  lead.     3.  Cupellation  of  the 

*  For  some  portions  of  the  following  method  of  assaying  gold  ores,  the 
Editor  is  indebted  to  Mr.  T.  M.  Blossom,  who  has  had  great  experience  in  the 
laboratory  of  the  School  of  Mines,  Columbia  College,  U.S.A.  (See*  Chemical 
News,'  Nos.  607,  609,  628,  635,  636.) 


G68  THE   ASSAY    OF    GOLD. 

lead  button,  by  which  the  lead  is  oxidised  and  absorbed  by 
the  cupel,  leaving  behind  a  bead  of  the  gold  and  silver. 
4.  Weighing  the  bead.  5.  Inquartation,  parting,  and  cu- 
pellation  of  the  gold  residue.  6.  Weighing  the  gold  bead. 

1.  Preparation  of  the  Sample. — It  is  essential,  in  the 
first  place,  to  obtain  a  fair  average  sample  of  the  ore, 
otherwise  the  results  of  the  assay  may  be  commercially 
worthless.     Selection  must  be  left  to  the  judgment  of  the 
assay er.     The  sample  must  be  dried,  if  necessary,  care 
being  taken  not  to  roast  it.     It  must  then  be  pounded  in 
an  iron  mortar  and  passed  through  a  sieve  of  eighty  meshes 
to  the  linear  inch.     If  any  native  metal,  in  the  form  of 
scales  or  filaments,  remain  upon  the  sieve,  take  the  weights, 
separately,  of  what  has  passed  through  and  of  what  is  left 
upon  the  sieve.     The  latter  must  be  assayed  according  to 
'  Assay  of  Alloys,'  and  the  result  referred  to  the  whole 
amount  of  ore.    It  is  essential  that  the  whole  of  the  sample, 
except  the  malleable  portion,  be  passed  through  the  sieve 
Mix  thoroughly  the  sifted  ore. 

2.  The  Collection  of  the  Gold  and  Silver  in  a  button 
of  metallic  lead  is  effected  in  a  crucible,  or  in  a  scorifier, 
whence  two  methods  of  assay  : — 

(a)  Crucible  assay.  (b)  Scorification  assay. 

The  former  is  applicable  to  all  ores ;  the  latter  is 
limited,  practically,  by  the  small  size  of  scorifiers,  to  the 
richer  ores. 

(a)  Crucible  Assay. — An  ore  of  gold  and  silver  is  com- 
posed of  precious  metal,  gangue,  and  oxides,  sulphides, 
&c.,  of  foreign  metals.  To  collect  the  precious  metals  in 
a  button  of  lead,  the  ore  is  mixed  with  litharge,  suitable 
fluxes,  an  oxidising  or  a  reducing  agent,  and  fused  in  the 
crucible.  Litharge  is  reduced  to  metallic  lead  ;  the  latter 
seizes  upon  the  precious  metals  and  collects  in  a  button  at 
the  bottom  of  the  crucible,  while  the  foreign  materials 
form,  with  the  fluxes,  a  fusible  slag  above  the  lead 
button.  The  crucible  is  broken  when  cold,  and  the  malle- 
able button  detached  from  the  slag  by  hammering  on  an 
anvil. 


GOLD    ORES.  669 

The  Charge. — The  weight  of  ore  taken  for  an  assay 
depends  upon  its  supposed  richness  or  poverty,  since  it  is 
required  to  obtain  finally  a  bead  of  precious  metal  of  con- 
venient size  for  weighing,  and,  at  the  same  time,  neither 
too  large  for  cupellation  (vide  cupellation)  nor  so  small 
as  seriously  to  affect  the  calculated  results,  through  losses 
sustained  in  the  assay.  As  a  rule,  it  is  usual  to  take  one, 
two,  or  four  assay  tons  for  gold  ores. 

The  ores  require  the  following  reagents  : — Litharge, 
sodium  carbonate,  and  one  of  the  reducing  agents,  argol 
and  charcoal,  or  an  oxidising  agent,  as  nitre,  with  invariably 
a  cover  of  salt  one-quarter  to  half  an  inch  in  depth. 
Borax,  silica,  and  other  reagents  are  very  useful  at  times, 
but  no  general  rule  can  be  given  for  their  employment. 
This  matter  must  be  left  to  the  judgment  of  the  assayer, 
guided  by  the  known  properties  of  the  reagents  and  by 
the  composition  of  the  ore.  It  is  well,  in  this  connection, 
to  bear  in  mind  the  principle  that  for  basic  impurities, 
an  acid  flux  is  needed,  and  for  an  acid  gangue  a  basic 
flux.  As  a  rule,  employ  a  weight  of  litharge  twice  that 
of  the  ore,  and  of  sodium  carbonate,  the  same  as  of  ore. 
These  proportions  also  may  be  modified  to  advantage, 
according  to  the  composition  of  the  ore.  The  propor- 
tion of  nitre,  or  of  reducing  agent,  depends  upon  the  re- 
ducing power  of  the  ore,  hence  it  is  variable  in  every  case. 
These  reagents  are  added  to  control  the  size  of  the  lead 
button. 

Size  of  the  Lead  Button. — There  are  two  limits  to  the 
size  of  the  button:  (1)  it  must  be  large  enough,  or,  in 
other  words,  enough  litharge  must  be  reduced  throughout 
the  mass  to  collect  all  the  precious  metal,  and,  at  the  same 
time  (2)  there  should  not  be  a  useless  excess  of  lead, 
which  would  occasion  loss  of  silver  in  the  subsequent 
cupellation. 

These  two  conditions  cannot  always  be  fulfilled,  but 
in  this  case  the  latter  must  be  sacrificed.  It  has  been 
found  that  a  button  of  15  to  20  grammes  is  the  best  size 
for  a  weight  of  ore  from  one-third  to  four  assay  tons. 
This  is  also  a  convenient  size  for  a  cupellation.  A  button 


670  THE   ASSAY   OF   GOLD. 

that  is  too  large  for  cupellation  can,  however,  always  be 
reduced  in  size  by  scorifying. 

These  requirements  necessitate,  in  many  instances,  a 
preliminary  assay  of  the  ore  to  determine  its  reducing 
power.  The  reducing  power  of  an  ore  is  due  to  the 
presence  of  sulphur,  arsenic,  antimony,  zinc,  &c.,  but 
generally  to  sulphur  contained  in  pyrites,  &c, 

Preliminary  Assay  of  Ore. 

Charge.     Ore.       V       '.  .  .     2  grms. 

Litharge    .         .  .  .25     „ 

Sodium  Carbonate  .  .  10     „ 

Salt  .         V       -;'•  ;  .  Cover. 

A  duplicate  assay  need  not  be  made. 

Warm  the  crucible  before  placing  it  in  the  fire,  which 
should  be  perfectly  bright,  and  should  be  urged  to  effect 
complete  fusion  in  the  shortest  possible  time.  When  the 
contents  of  the  crucible  are  in  quiet  fusion,  it  must  be 
withdrawn,  to  prevent  further  reducing  action  of  the 
furnace  gases.  Tap  the  crucible  gently,  and  when  cold 
break  it  open. 

Three  cases  may  arise  here.  Two  grammes  of  ore  may 
yield — 

1.  No  lead,  or  less  than  three  grammes, 

2.  Three  grammes  lead. 

3.  More  than  three  grammes. 

The  reducing  power  is  stated  thus  :  2  grms.  ore 
=#  grins,  lead.  Let  us  suppose  that  we  shall  take  for  the 
regular  assay  J  assay  ton  of  ore,  and  that  the  reducing 
power  is  found  to  be  2  grms.  ore  =  1*5  grms.  lead  :  ^  assay 
ton  or  10  grms.  (about)  ore  will  in  this  case  reduce  7'5 
grms.  lead,  and  as  the  required  button  is  15  grms.,  we 
must  add  enough  argol,  or  charcoal,  to  reduce  7 '5  grms. 
in  addition  ;  taking  argol  as  8*5,  we  shall  require  7*5-*- 8'5 
grms.  or  0-882  grms.,  say  1  grm.,  or  charcoal  7*5^-28 
=  0-268,  say  0-3  grm. 

If  the  reducing  power  correspond  to  the  third  case,  a 


GOLD   ORES.  671 

similar  calculation  will  indicate  how  much  nitre  is  needed 
to  oxidise  part  of  the  sulphur,  arsenic,  or  other  reducing 
agent,  and  thus  prevent  the  reduction  of  a  button  larger 
than  15  grammes.  In  the  second  case,  ten  grammes  of 
ore  would  reduce  a  button  of  15  grms.,  and  neither  argol 
nor  nitre  would  be  required. 

The  character  of  slag  obtained  in  the  preliminary  assay 
may  also  suggest  some  modification  of  the  regular  charge. 
If  it  be  earthy,  for  instance,  we  would  add  borax-glass  or 
silica.  Experience  will  often  enable  the  assay er  to  judge 
of  the  reducing  power  with  sufficient  exactness,  without  an 
extra  assay.  Cases  will  arise,  however,  in  which  he  must 
make  a  preliminary  assay,  or  roast  the  ore,  and  it  is 
always  best  to  roast  when  there  is  a  large  amount  of 
sulphur  in  the  ore.  He  will  then  have  an  ore  of  no 
reducing  power. — (Case  I.) 

Ores  to  be  Roasted. — Ores  containing  a  large  amount  of 
sulphur,  or  arsenic,  antimony  or  zinc,  should  always  be 
roasted.  In  the  former  case  if  the  ore  be  not  roasted, 
there  will  be  danger  of  the  formation  of  oxysulphides, 
which  are  very  fusible,  but  are  not  decomposed  even  at  a 
white  heat,  and  enter  the  slag  carrying  silver  with  them. 
A  large  quantity  of  nitre  also  subjects  the  contents  of  the 
crucible  to  the  liability  of  boiling  over :  even  should  this 
mishap  not  occur,  the  great  evolution  of  nitrous  and  sul- 
phurous vapours  puffs  up  the  mass  throughout  the  cru- 
cible, and  the  globules  of  lead  afterward  reduced  may  be 
left  adhering  to  the  sides,  not  being  washed  down  by  the 
retreating  charge.  Arsenic  and  antimony  produce  arseni- 
ates  and  antimoniates,  which  carry  silver  into  the  slag. 
Zinc  increases  the  loss  of  silver  by  volatilisation  and  also  in 
the  slag. 

Roasting  the  Ore. — The  ore  may  be  roasted  conveniently 
in  a  cast-iron  pan  over  the  crucible  furnace.  There  ought 
to  be  a  hood  over  the  furnace,  to  carry  off  the  fumes  of 
sulphurous,  arsenious,  and  other  acids.  The  pan  should 
be  covered  with  a  coating  of  red  ochre,  or,  still  better, 
of  chalk.  The  former  is  put  on  wet  with  a  brush.  An 
excellent  even  coating  of  the  latter  may  be  obtained  by 


672  THE    ASSAY   OF    GOLD. 

making  a  chalk  paste,  of  proper  consistence,  in  the  pan, 
and  turning  with  the  hand  so  as  to  spread  the  paste  while 
the  pan  is  being  held  over  the  fire  to  dr}^.  The  coating 
prevents  a  loss  of  ore  and  injury  to  the  pan  through  the 
sulphides  attacking  the  iron. 

The  weighed  sample  must  be  spread  over  the  pan  and 
stirred  with  a  bent  wire  until  all  danger  of  fusion  is  past. 
The  pan  must  be  heated  gradually  at  first,  not  above  a 
dull  red  heat  for  some  time,  and  may  be  brought,  finally, 
to  a  full  red,  or  higher  heat.  Too  high  a  heat  at  the 
outset  might  cause  the  fusion  of  sulphides  and  the  forma- 
tion of  matter  troublesome  to  roast.  A  rapid  disengage* 
ment  of  arsenic,  antimony,  or  zinc,  would  cause,  also,  a 
mechanical  loss  of  silver,  by  carrying  if  off  in  their  vapours. 
Should  fusion  take  place,  it  is  better  to  weigh  out  a  fresh 
portion  of  ore  and  roast  again  with  more  care.  If  this  be 
not  done  the  fused  portions  must  be  pulverised  in  a  mortar 
and  re-roasted.  Generally,  in  roasting  sulphides,  the 
operation  may  be  considered  finished  when,  after  keeping 
the  pan  at  a  full  red  heat  for  some  time,  no  more  fumes  of 
sulphurous  acid  can  be  perceived.  As  there  is  danger, 
however,  of  the  formation  of  sulphates,  especially  if  copper 
pyrites  be  present,  it  is  best  always  to  mix  some  ammo- 
nium carbonate  with  the  ore,  after  the  fumes  have  ceased, 
and  to  cover  the  pan.  The  ore  is  thus  confined  in  an 
atmosphere  of  ammonium  carbonate,  which  decomposes 
the  sulphates  with  formation  of  volatile  sulphate  of 
ammonia. 

Arsenic  and  antimony  require  the  addition  of  fine 
charcoal,  to  reduce  any  arseniates  and  antimoniates  that 
may  have  been  formed  during  the  roasting.  Care  must 
be  taken  to  burn  out  all  the  charcoal. 

If  the  ore  contain  a  very  fusible  sulphide,  as  antimony- 
glance  or  galena,  it  may  be  mixed  with  some  fine  sand 
previous  to  roasting. 

The  roasting  of  ores  may  also  be  done  in  the  muffle  in 
an  earthen  saucer. 


GOLD   ORES.  673 


Fusion. 

The  charge  prepared  according  to  the  foregoing  direc- 
tions is  thoroughly  mixed  and  placed  in  a  crucible,  which 
it  should  not  more  than  two-thirds  fill.  A  hot  fire  should  be 
employed,  and  the  crucible  removed  when  complete  fusion 
has  taken  place.  This  ought  to  require  from  twenty  to 
twenty-five  minutes.  The  crucible  is  tapped,  as  usual,  and 
broken  when  cold. 

(b)  Scarification  Assay.  The  reagents  necessary  for  a 
scorification  assay  are  test -lead  and  borax-glass.  The  ore 
is  mixed  with  these  in  suitable  proportions,  the  mixture 
put  in  a  scorifier  and  fused  in  a  muffle.  The  operation 
affords  an  alloy  of  lead  with  the  precious  metals,  and  a 
slag  composed  of  li tharge  with  the  impurities  and  gangue 
of  the  ore.  The  assay  might  be  made  with  lead  only, 
but  it  is  advantageous  to  add  some  borax.  There  will  be 
required  of  lead  only  enough  to  render  the  slag  liquid  and 
to  furnish  lead  for  the  button.  The  proportions  of  both 
lead  and  borax  will  vary,  and  should  be  greater  in  pro- 
portion as  the  gangue  and  metallic  oxides  are  more  diffi- 
cult of  fusion.  The  following  table  exhibits  the  propor- 
tions found  by  experience  to  be  best  adapted  to  the 
different  gangues.  The  proportions  are  referred  to  one 
part  of  ore. 

Parts  Parts 

Character  of  Gangue  Test-Lead  Borax 

Quartzose 8 

Basic  (Fe2O,,Al2O3»  CaO),  &c.       .  8  0-25-1-00 

Galena 5-6  0-15 

Arsenical 16  010-0-50 

Antimonial 16  0-10-1-00 

Fahlerz 12-16  0-10-0-15 

Iron  pyrites 10-15  0-10-0-20 

Blende 10-15  0-10-0-20 

No  preliminary  roasting  is  required.  As  in  the  cru- 
cible assay,  the  weight  of  ore  taken  depends  very  much 
upon  its  richness,  but  is  generally  a  third,  sixth,  or  tenth 
of  an  assay  ton.  If  one  scorifier  will  not  contain  the 
charge,  it  is  best  to  weigh  equal  fractional  parts  for  the 
number  required,  rather  than  to  weigh  the  whole  charge 

x  x 


674  THE  ASSAY   OF   GOLD. 

and  roughly  divide  it  between  the  ecorifiers.  In  case  of 
an  accident  to  one  of  the  scorifiers,  the  known  loss  can 
easily  be  restored,  if  the  former  course  be  followed.  The 
exact  parts  that  lead  and  borax  perform  in  scorificatioii 
can  be  understood  best  from  a  description  of  the  operation 
in  detail. 

Three  distinct  periods  may  be  noted  in  the  working  : — 
1.  Boasting  ;  2.  Fusion ;  3.  Scorification.  A  strong 
heat  is  maintained,  at  first,  in  order  to  melt  the  lead. 
This  is  effected  by  closing  the  muffle  and  regulating  the 
draught.  As  soon  as  the  lead  is  fused  the  muffle  is 
opened,  and  the  ore  is  seen  floating  upon  the  surface  of 
the  lead. 

1.  The  roasting  now  commences,  and  is  continued  at 
a  moderate  heat  until  no  more  fumes  are  seen,  and  the 
ore  has  disappeared. 

2.  The  heat  should  now  be  raised  in  order  to  fuse 
thoroughly  all  the  material  in  the  scorifier.     When  the 
fusion  is  complete,  clear  white  fumes  of  lead  may  be  seen 
arising  from  the  scorifier,  there  is  an  intermittent  play  of 
colours  across  the  bright  surface  of  the  lead,  and  the  slag 
produced  encircles  the  metallic  bath  like  a  ring.     The 
borax  plays  an  important  part  just  here,  by  giving  liquidity 
to  the  slag,  thus  permitting  it  to  be  thrown  to  the  side  as 
fast  as  formed,  exposing  a  clear  surface  of  lead  for  oxida- 
tion.    If  borax  be  not  added  and  the  ore  contain  a  diffi- 
cultly fusible  gangue,  the  scoria3  will  float  in  detached 
masses  over  the  lead,  impeding  the  oxidation,  until  suffi- 
cient litharge  has  been  formed  to  give  it  liquidity. 

3.  When  the  fusion   is   complete,  the  heat   may   be 
lowered  and  the  third  period  of  scorification  continued 
until   the   ring    of  slag,   which    is    continually   growing 
smaller,  closes  over  the  residue  of  metallic  lead.     The  heat 
should  again  be  raised,  to  liquefy  the  slag  and  allow  the 
metallic  lead  to  settle,  after  which  the  scorifier  is  removed 
from  the  furnace.     If  the  button  is  wanted  immediately 
for  cupellation,  the  contents  of  the  scorifier  may  be  poured 
into  an  iron  or  copper  mould  coated  with  red  ochre.     It 
is  thus  soon  cooled.      Otherwise  allow  the   contents   to 


CUPELLATIOX.  675 

solidify  in  the  scorifier,  and  break  this   for  the  "button 
when  cold.     Hammer  the  button  as  usual. 

The  whole  assay  occupies  about  thirty-five  minutes. 

In  making  the  charge,  it  is  customary  to  mix  the  ore 
with  a  part  of  the  test-lead  and  with  borax,  and  to  cover 
this  in  the  scorifier  with  the  rest  of  the  lead.  This  will 
prevent  loss  of  ore  prior  to  fusion.  Too  much  borax 
should  not  be  added  at  first.  If  a  large  amount  is  needed, 
it  is  better  to  mix  only  a  portion  with  the  ore — one  gramme, 
for  instance — and  to  introduce  the  rest  wrapped  up  in 
paper,  as  needed  during  the  operation.  Some  of  it  may 
be  reserved  for  the  final  heating  after  the  lead  is  slagged 
over.  If  too  much  Avere  added  at  first,  the  lead  would  be 
slagged  over  before  the  necessary  reactions  had  taken 
place. 

The  Lead  Button. — The  lead  button  submitted  to  cupel- 
lation  must  be  malleable  and  of  the  proper  size  for  the 
cupel.  A  good  cupel  will  absorb  its  own  weight  of 
litharge,  but  it  is  better  to  use  a  cupel  one- quarter  to  a 
third  as  heavy  again  as  the  lead  button.  The  cupels  in 
ordinary  use  weigh  about  18  grammes,  hence  a  button  of 
12  to  15  grammes  is  the  proper  size  for  them.  If  the 
button  be  too  large  it  may  be  reduced  in  size  by  scorifica- 
tion. In  case  of  doubt  it  is  better  to  scorify,  since  there  is 
less  loss  in  this  operation  than  in  cnpellation.  A  brittle 
button  may  be  due  to  the  presence  of  sulphur,  arsenic, 
antimony,  zinc,  or  litharge.  In  either  case  it  must  be 
scorified  before  cupellation,  and  with  test-lead  if  necessary. 
If  the  button  contain  copper  it  must  be  scorified  until  no 
more  copper  can  be  seen  on  hammering  out  the  button. 
If  nickel  be  present  the  button  cannot  be  cupelled.  This, 
however,  will  occur  but  rarely. 

3.  Cupellation. — The  lead  button  obtained  by  the  fore- 
going operations  is  next  cupelled.  This  operation  is 
similar  in  many  respects  to  scorification,  but  differs  from  it 
in  that  the  scoria?  formed  are  absorbed  entirely  by  the 
cupel,  leaving  a  pure  bead  of  the  precious  metals.  This 
property  of  the  absorption  of  scoriae  is  an  indispensable 
condition  in  cupellation,  so  that,  unlike  scorification,  it  is 


676  THE   ASSAY   OF    GOLD. 

limited  to  a  few  substances  capable  of  being  absorbed  by 
the  cupel.  The  oxides  of  lead  and  bismuth  alone  can  be 
absorbed  in  a  state  of  purity,  but  they  can  carry  along 
with  them  certain  proportions  of  other  substances  which, 
by  themselves,  would  form  infusible  scoria.  It  is  thus 
that  we  are  enabled  to  get  rid  of  small  amounts  of  copper, 
iron,  arsenic,  &c.,  remaining  in  the  lead  button.  Bismuth  is 
seldom,  if  ever,  used  for  this  purpose.  Th'e  proportion  of 
lead  required  to  carry  off  the  different  impurities  varies 
according  to  circumstances.  In  the  case  of  lead  buttons 
from  an  assay,  there  is  always  an  excess  of  lead,  if  they 
have  been  properly  purified.  Other  cases  will  be  treated 
under  the  head  of  Assay  of  Alloys,  where  the  necessary 
tables  will  be  given. 

The  operation  of  cupelling  a  lead  button  is  conducted 
as  follows  : — 

The  cupels  must  be  carefully  dried  before  use,  and 
must  be  free  from  cracks,  which  would  cause  a  loss  of 
precious  metal.  The  bottom  of  the  muffle  should  be 
covered  with  sand  to  prevent  injury  to  it  in  case  of  the  up- 
setting of  a  cupel.  A  cupel  having  been  selected,  it  should 
be  wiped  carefully  with  the  finger,  and  all  extraneous 
matter  blown  out.  It  may  then  be  placed  in  the  muffle. 
Before  the  introduction  of  the  lead  button,  the  muffle 
should  have  attained  a  reddish -white  heat,  and  the  cupel 
should  be  of  the  same  temperature.  This  being  attained, 
the  button  is  placed  in  the  cupel  with  a  pair  of  forceps, 
gently,  so  as  not  to  injure  it.  The  muffle  should  now  be 
closed,  either  by  a  door  or  by  a  piece  of  lighted  charcoal, 
to  bring  the  fused  button  to  the  same  temperature.  This 
done,  the  muffle  is  opened  and  air  allowed  to  enter  ;  the 
button,  which  at  first  appears  bright  and  uncovered,  is 
soon  covered  with  a  film  of  oxide  moving  in  luminous 
patches  over  the  surface,  arid  being  continually  thrown 
toward  the  edge,  where  it  is  absorbed  by  the  cupel.  White 
fumes  of  lead  arise,  and  the  button  is  surrounded  by  a 
ring  of  the  absorbed  litharge,  which  continually  widens 
until  it  reaches  the  edge  of  the  cupel.  The  button  thus 
gradually  diminishes  in  size  by  oxidation  and  absorption, 


CUPELLATIOX.  677 

and  becomes  more  convex  ;  the  luminous  patches  become 
larger  and  move  more  quickly  ;  and  when,  finally,  the  last 
of  the  lead  is  absorbed,  the  button  appears  to  revolve 
rapidly  on  its  axis,  becomes  very  brilliant,  and  is  suffused 
with  all  the  tints  of  the  rainbow ;  the  movement  is  sud- 
denly checked,  the  button  becomes  dull  for  a  few  instants, 
and  then  presents  the  appearance  of  the  pure  precious 
metals.  The  latter  part  of  the  operation  is  called  the 
4  brightening '  of  the  button.  Should  the  bead  be  large, 
and  composed,  in  great  part  at  least,  of  silver,  it  must  be 
removed  slowly  and  gradually  from  the  furnace,  to  pre- 
vent loss  by  '  spitting,'  which  might  happen  if  the  cupel 
were  removed  at  once  from  the  muffle.  When  a  cupel  is 
withdrawn  directly  after  brightening,  the  button  is  liable 
to  be  covered  by  mammillated  and  crystalline  protuber- 
ances, and  is  then  said  to  have  '  vegetated '  or  '  spit.' 
Portions  of  the  metal  are  sometimes  thrown  off  and  lost. 
Whatever  the  cause  may  .be,  this  does  not  occur  if  the 
button  be  withdrawn  gradually,  so  as  to  permit  a  slow  and 
gradual  cooling.  In  case  the  bead  be  very  large,  say  100- 
300  milligrammes,  it  is  well  to  cover  it  with  a  hot  cupel, 
which  will  retard  the  cooling  and  prevent  the  loss  of  small 
particles  that  may  be  thrown  off  despite  all  care.  If  the 
bead  is  not  larger  than  the  head  of  an  ordinary  pin,  the 
danger  of  vegetation  is  slight,  and  no  great  precautions 
need  be  taken  in  its  removal. 

It  is  well  to  raise  the  heat  of  the  furnace  just  before 
the  brightening,  or  to  push  the  cupel  into  a  hotter  part 
of  the  muffle,  in  order  to  aid  the  brightening  and  get  rid 
of  the  last  traces  of  lead,  which  are  somewhat  difficult  to 
remove.  The  button  should  also,  for  the  latter  purpose, 
be  heated  strongly  a  few  seconds  after  brightening. 

Silver  is  sensibly  volatile  at  a  high  heat ;  the  loss  of 
gold  is  slight,  and  may  be  disregarded.  In  the  assay  of 
ores  this  loss  need  not  be  considered,  but  in  bullion  assay 
a  correction  is  necessary,  for  which  a  table  will  be  given 
under  Assays  of  Alloys.  The  loss  of  silver  increases  with 
the  temperature,  but  we  must  avoid,  in  cupellation,  the 
two  extremes  of  a  high  heat  and  quick  work  and  a  low 


078  THE  ASSAY  'OF   GOLD. 

heat  with  prolonged  work.  Of  the  two  extremes  the  latter 
is  worse.  The  following  are  indices  of  favourable  work- 
ing : — The  muffle  is  reddish -white,  the  cupel  is  red,  the 
fused  metal  very  luminous  and  clear,  the  lead  fumes  rise 
slowly  to  the  top  of  the  muffle,  and  the  litharge  is  com- 
pletely absorbed  by  the  cupel. 

The  heat  is  too  great  when  the  cupels  are  whitish,  when 
the  fused  metal  is  seen  with  difficulty,  and  the  scarcely- 
visible  fumes  rise  rapidly  in  the  muffle. 

The  heat  is  too  low  when  the  fumes  are  thick  and  fall 
in  the  muffle,  and  when  the  unabsorbed  litharge  is  seen 
forming  lumps  and  scales  about  the  button. 

The  degree  of  heat  should  bear  some  relation  to  the 
richness  of  the  alloy,  and  may  be  greater  according  as 
the  lead  is  poorer  in  silver.  By  bearing  this  in  mind  the 
assay er  may  often  hasten  the  operation  without  detriment 
to  the  assay.  The  draught  of  air  through  the  muffle  must 
also  be  regulated.  Too  strong. a  current  cools  the  cupel 
and  oxidises  the  lead  faster  than  it  can  be  absorbed,  thus 
endangering  the  assay.  Too  slow  a  current  prolongs  the 
operation  and  increases  the  loss  by  volatilisation.  In 
ordinary  work  this  matter,  however,  occasions  very  little 
trouble. 

It  happens  sometimes  that  the  material  in  the  cupel 
becomes  solidified  in  the- midst  of  an  operation,  stopping 
all  further  action.  This  disaster  is  called  the  '  freezing  '  of 
the  button,  and  is  occasioned  by  the  following  conditions  ; 
a  production  of  litharge  more  rapidly  than  it  can  be  ab- 
sorbed by  the  cupel,  and  infusible  scorias,  due  to  a  cold 
furnace,  or  to  an  excess  of  foreign  oxides.  In  either  case 
the  scoriae  gradually  extend  over  the  surface  of  the  button 
until  it  is  entirely  covered,  when  further  movement  ceases. 
This  disaster  may  sometimes  be  prevented  or  remedied  by 
raising  the  heat  of  the  muffle  ;  if  this  fails,  or  if  the  acci- 
dent be  due  to  foreign  oxides,  an  addition  of  pure  lead 
must  be  made  to  the  assay  ;  in  either  case,  the  results  are 
unreliable. 

An  assay  that  has  passed  well,  furnishes  a  bead  well- 
rounded  and  clear,  crystalline  below,  and  readily  to  be 


CUPELLATION.  679 

detached  from  the  cupel.  If  the  bead  contain  lead,  it  is 
brilliant  below,  and  does  not  adhere  at  all  to  the  cupel. 
If  the  bead  exhibits  rootlets  passing  down  into  the  sub- 
stance of  the  cupel,  the  results  are  inaccurate. 

GENERAL   OBSERVATIONS   ON   THE   ASSAY   OF   GOLD    ORES. 

Gold  and  Copper,  Proportion  of  Lead. —  The  alloys  of 
gold  and  copper  are  cupelled  like  the  alloys  of  gold  and 
silver ;  but  as  copper  has  a  very  great  affinity  for  gold,  it 
is  necessary  to  use  a  larger  proportion  of  lead  to  ensure 
its  oxidation  when  combined  with  gold  than  when  united 
with  silver.  This  proportion  varies  according  to  the 
standard  and  the  temperature.  It  is  admitted  that  for  the 
same  standard  there  must,  under  similar  circumstances,  be 
twice  as  much  lead  used  in  the  cupellation  of  gold  as  for 
that  of  silver.  Thus,  14  parts,  at  least,  ought  to  be  em- 
ployed in  common  furnaces  for  an  assay  of  gold  coin 
which  contains  0*1  of  copper.  There  is  no  inconvenience 
in  employing  a  little  more,  as  it  does  not  increase  the  loss 
of  gold.  However  great  the  proportion  of  lead  may  be 
that  is  added  to  the  cupreous  gold  for  the  purpose  of 
cupellation,  the  button  retains  always  a  very  small  quantity 
of  copper,  which  a  fresh  cupellation  does  not  free  it  from, 
and  which  occasions  what  is  termed  the  surcharge.  This 
surcharge,  being  very  slight,  can  be  neglected  in  assays  of 
minerals  ;  but  it  is  necessary  to  take  notice  of  it  in  the 
assay  of  alloys.  But  it  is  known  that  the  presence  of 
silver  much  facilitates  the  separation  of  copper  from  gold, 
and  it  is  rare  that  an  alloy  of  cupreous  gold  does  not  con- 
tain a  little  silver,  which  must  be  separated  :  and  when  that 
is  not  the  case,  a  small  quantity  of  that  metal  can  be 
introduced  into  the  alloy,  so  as  to  be  in  about  the  propor- 
tion of  3  parts  to  1  of  gold.  When  an  assay  is  to  be  made 
of  an  alloy  of  gold  and  copper,  a  sufficient  quantity  of 
silver  is  to  be  added  to  fulfil  this  condition  according  to 
the  presumed  standard,  which  is  determined  approxi- 
matively  by  a  preliminary  assay,  and  then  cupelled  with 
lead. 


680  THE   ASSAY   OF   GOLD. 

Examination  on  the  Touchstone. — This  method  is  based 
upon  the  fact,  that  the  richer  an  alloy  is  in  gold  the  more 
clearly  does  a  streak  drawn  with  it  on  a  black  ground 
present  a  pure  gold-yellow  colour,  and  the  less  is  it 
attacked  by  pure  nitric  acid  or  by  a  test  acid.  This  test 
acid  consists  of  ninety-eight  parts  pure  nitric  acid  of  1'34 
spec.  grav.  (37°  Beaume),  two  parts  pure  hydrochloric 
acid  of  1'173  spec.  grav.  (21°  B.),  and  twenty-five  parts 
distilled  water.  To  judge  of  the  richness  of  the  alloy  to 
be  examined,  its  streak  is  compared  with  marks  drawn 
with  alloys  (the  touch-needles)  whose  richness  is  accurately 
known.  In  order  to  get  correctly  the  streak  of  the  alloy 
to  be  tested,  the  surface  of  the  metal  must  first  be  some- 
what filed  away,  since  this  may  be  impure,  or,  as  with 
coins  and  jewellery,  it  may  have  been  made  somewhat  richer 
by  boiling  with  acid,  and  the  so-called  colouring  of  the 
goldsmith,  and  a  clean  fracture  is  rarely  to  be  obtained. 
Five  series  of  prepared  touch-needles  are  required.  The 
first  series  consists  of  copper  and  gold,  and  is  called  the 
red  series,  and  the  proportion  of  gold  increases  by  half- 
carats  in  the  successive  needles.  The  second  series,  the 
white  series,  contains  needles  of  gold  and  silver,  in  which 
the  proportion  of  gold  likewise  increases  by  half- carats. 
The  third  series,  a  mixed  one,  contains  needles  in  which  the 
quantities  of  silver  and  copper  are  equal,  and  the  propor- 
tion of  gold  also  increases  by  half-carats.  The  fourth  con- 
sists also  of  needles  for  a  mixed  series,  in  which  the  silver 
is  to  the  copper  as  2  :  1,  and  the  gold  increases  by  half- 
carats  ;  and  the  fifth  is  also  formed  of  needles  for  a  mixed 
series,  in  which  the  quantity  of  silver  is  to  that  of  the 
copper  as  1  :  2.  Moreover,  in  mints  and  stamping  bureaux, 
alloys  are  used  which  correspond  precisely  to  the  legal 
standards.  The  testing  upon  the  touchstone  begins  by 
determining  to  which  series  the  alloy  to  be  examined  be- 
longs. Then  those  touch-needles  are  rubbed  against  the 
stone  whose  marks  most  nearly  approximate  in  colour  to 
that  of  the  alloy.  The  marks  must  form  a  thin  continuous 
layer.  A  drop  of  pure  nitric  acid  is  now  placed  upon 
them  with  a  glass  rod,  and  its  comparative  effect  observed. 


EXAMINATION   OX   THE   TOUCHSTONE. 


681 


The  acid  is  allowed  to  work  a  short  time,  and  then  wiped 
off,  in  order  to  see  whether  the  streak  appears  unchanged, 
or  whether  it  has  more  or  less  disappeared.  The  test  acid 
above  is  also  used.  This  is  so  composed  that  it  does  not 
work  at  all  upon  an  alloy  containing  eighteen  carats  and 
more  of  gold,  and  with  such  an  alloy  the  streak,  after 
using  the  acid,  will  not  be  wiped  off  with  a  fine  linen  rag, 
provided  that  stone  and  acid  had  a  temperature  of  10  to 
12°  C.  Pure  nitric  acid  produces  almost  no  effect  upon  an 
alloy  of  fifteen  or  sixteen  carats  fine,  and  over.  The  test- 
ing on  the  touchstone  can  indeed  make  no  pretension  to 
accuracy,  especially  where  the  amount  of  gold  is  small, 
but  it  yields  sufficiently  useful  results  for  a  preliminary 
test.  It  requires,  however,  a  sharp  and  very  practised  eye. 
Moreover,  the  preparation  of  the  touch-needles  is  weari- 
some, as  the  required  proportion  is  not  always  quickly 
reached,  nor  are  good  malleable  alloys  always  obtained. 
The  touchstone,  therefore,  is  in  general  only  used  where 
frequent  gold  assays  are  to  be  made  of  alloys  varying  in 
richness,  or  where  (as  frequently  with  gold  plate)  an  ex- 
amination on  the  touchstone  will  suffice. 

TABLE  FOR  PROPORTION  OF  LEAD  TO  BE  EMPLOYED  ix  THE 

CUPELLATION   OF  GOLD   AND  COPPER. 

Ratio  of  lead  in 
the  assay  to  the 


Gold  in 

000th 
900 
800 
700 
600 
500 
400) 
300 
200  }• 
100 
50 

alloy                                                           Lead  required 

ousandths       ....       1  part 
.     10  parts 

copper,  Sic. 

100,000: 
80,000: 
73,333  : 
60,000  : 
52,600  : 
[56,666: 
48,571  : 
42,500: 
37,377  : 

1 
1 
1 
1 
1 
1 
1 
1 
1 

.         .        •         •        •     16    „ 

22 

«    f*  - 

34 

Kandelhardt  gives  the  ratio  in  the  following  table : — 


Gold  in  1000  parts 

1000  fine  gold 
980  —  920 
920  —  875 
875  —  750 
750  —  600 
600  —  350 
350—     0 

8 

16 
20 
24 

28 
32 

Quantity  of  lead  required 

8  times  the  weight  of  the  alloy 


682  THE   ASSAY   OF    GOLD. 

Gold,  Silver,  Platinum,  and  Copper. — The  presence  of 
platinum  in  an  alloy  renders  the  separation  of  the  oxi- 
disable  metals,  more  especially  copper,  very  difficult  by 
cupellation.  It  appears,  indeed,  that  it  would  be  almost 
impossible  to  arrive  at  it,  if  the  alloy  of  copper  contained 
nothing  but  gold  and  platinum.  It  is  necessary  that  silver 
be  present  at  the  same  time.  When  this  metal  is  absent, 
it  is  requisite  to  add  a  quantity  of  it,  which  ought  to  be 
equivalent  to  double  the  weight  of  the  gold  and  platinum 
united,  and  cupel  at  the  strongest  heat  which  can  be  ob- 
tained in  a  good  muffle  with  a  suitable  proportion  of  lead. 
This  proportion  varies  much  according  to  the  composition 
of  the  alloy,  and  the  teinperature  at  which  the  operation 
is  carried  on.  u-v 

Experience  has  shown  that  the  copper  can  be  more 
completely  separated  and  less  silver  lost  by  cupelling  at  a 
high  temperature,  with  the  least  possible  quantity  of  lead, 
than  by  employing  more  lead,  and  working  at  a  lower  tem- 
perature. M.  Chaudet  has  made  several  assays,  in  order 
to  determine  the  proportion  of  lead  required  for  the  cupel- 
lation of  the  three  following  alloys  : — 

1.  2.  3. 

Gold.,=    V    .^V^^'-'V      .    0-100  0-020  0-005 

Platinum    .        .        .        ,        .     O'lOO  0*200  0-300 

Silver     ,V       w;     vjStiJf        -     0-250  0-580  0-595 

Copper     ~  .-      v    •..  ,    r    .  .-    .     0-550  0-200  0100 

and  has  found,  for  the  first,  that  by  employing  20  parts  of 
lead  the  separation  is  very  nearly  complete ;  but  that  at  a 
high  temperature  there  is  a  loss  of  silver,  and  in  order  to 
render  the  assay  correct,  it  must  be  cupelled  at  the  latter 
temperature,  with  only  14  of  lead;  for  the  second,  8  of 
lead,  at  a  high  temperature  ;  and  for  the  third,  30  parts 
of  lead  are  necessary,  at  the  same  high  temperature  of  the 
muffle ;  but  it  is  almost  impossible  to  separate  all  the 
copper,  and  no  advantage  can  be  obtained  by  increasing 
the  quantity  of  lead.  When  almost  the  last  traces  of  the 
copper  are  separated,  the  button  must  be  cupelled  afresh, 
with  a  small  quantity  of  lead ;  but  a  small  quantity  of 
silver  is  nearly  always  lost.  In  all  cases,  in  order  that  no 


ASSAY   OF   GOLD   ALLOYS.  683 

lead  shall  remain,  it  is  necessary  to  leave  the  assay  button 
some  few  minutes  in  the  muffle  after  cupellation  is  finished. 

The  alloys  of  gold  and  silver  which  contain  platinum 
show,  either  by  cupellation  or  parting,  certain  characters 
which  prove  the  presence  of  the  metal.  If  the  assay  be 
not  heated  very  strongly,  it  does  not  pass,  and  the  button 
becomes  flat ;  this  effect  becomes  very  sensible  when  the 
platinum  is  to  the  gold  in  the  proportion  of  2  to  100. 
Under  the  same  circumstances,  the  nitric  acid  solution 
proceeding  from  the  parting  is  coloured  straw-yellow. 
At  the  moment  an  assay  of  an  alloy  containing  platinum 
terminates,  the  motion  is  slower,  and  the  coloured  bands 
are  less  numerous,  more  obscure,  and  remain  a  much 
longer  time  than  when  there  is  no  platinum ;  the  button 
does  not  uncover,  and  the  surface  does  not  become  as 
brilliant  as  that  of  an  alloy  of  gold  or  silver,  but  it  remains 
dull  and  tarnished.  When  the  assay  is  well  made,  it  is  to 
be  remarked  that  the  edges  of  the  button  are  thicker  and 
more  rounded  than  in  ordinary  assays,  and  it  is  of  a  dull 
white,  approaching  a  little  to  yellow  ;  and  lastly,  its  sur- 
face is  wholly  or  in  part  crystalline.  These  effects  are 
sensible  even  when  the  gold  does  not  contain  more  than 
O'Ol  of  platinum.  When  the  alloy  contains  more  than  10 
parts  of  platinum  to  90  of  gold,  the  annealed  cornet  pro- 
duced in  the  parting  process  is  of  a  pale  yellow,  or  tar- 
nished silver  colour. 

Gold  alloyed  with  Silver. — The  separation  of  gold  from 
silver  is  termed  parting.  Parting  is  not  only  used  to  sepa- 
rate silver  from  gold,  but  for  the  separation  of  other  metals, 
such  as  copper,  when  cupellation  does  not  separate  it 
entirely.  Parting  by  the  wet  process  is  carried  on  by  the 
means  of  nitric  acid,  aqua  regia,  or  sulphuric  acid. 

When  an  alloy  of  gold  and  silver  has  been  reduced  by 
a  flatting  mill  to  very  thin  plates,  it  is  sufficient  that  it 
contains  2  ^  of  silver  to  1  of  gold  in  order  that  the  parting 
may  be  effected  completely  by  nitric  acid,  and  takes  place 
much  less  easily  when  the  silver  in  the  alloy  is  in  larger 
proportion  ;  but  when  this  proportion  exceeds  3  parts  of 
silver  for  1  of  gold,  then  the  latter  is  obtained  in  leaves  so 


684  THE   ASSAY   OP   GOLD. 

fine,  that  there  is  risk  incurred  of  losing  some  in  the  sub- 
sequent manipulation,  and  even  by  the  act  of  boiling  the 
acid  liquid. 

We  must  always,  therefore,  when  a  very  exact  assay  is 
required,  contrive  that  the  alloy  shall  contain  a  little  less 
than  3  parts  of  silver  to  1  of  gold,  a  proportion  which 
long  experience  has  demonstrated  to  be  the  best.  If  the 
alloy  contain  less  than  2^  of  silver  to  1  of  gold,  the  silver 
does  not  wholly  dissolve,  because  there  is  a  part  of  it  so 
enveloped  in  the  gold  that  the  strongest  acid  does  not  act 
on  it.* 

Inquartation. — The  operation  by  which  the  alloy  is 
brought  to  this  standard  is  termed  quartation,  or  inquar- 
tation.  It  consists  in  fusing  the  alloy  in  a  cupel,  with  2 
parts  of  lead  and  the  quantity  of  fine  silver,  or  fine  gold, 
necessary  to  bring  it  to  the  desired  composition.  This 
quantity  is  estimated  according  to  the  approximative  deter- 
mination of  the  standard  of  the  alloy,  which  ought  to  be 
made  either  by  means  of  a  preliminary  assay,  as  hereafter 
described,  or  by  means  of  the  touchstone.  If  we  do  not 
employ  the  whole  of  the  alloy  the  assay  will  not  be  exact, 
because  the  gold  and  silver  are  not  always  found  dis- 
tributed in  an  uniform  manner ;  at  least  every  time  it  is 
not  poured  into  a  cold  ingot  mould. 

Operation. —  The  cupelled  and  quartated  button  is 
flattened  on  an  anvil  and  annealed,  in  order  to  soften  it. 
It  is  laminated  to  give  it  a  certain  thickness,  and  is  then 
annealed  afresh,  and  rolled  into  a  cornet  or  spiral  around 
the  quill  of  a  pen.  It  is  necessary  that  the  alloy  should 
be  reduced  to  a  suitable  thickness,  on  the  one  hand,  in 
order  that  the  silver  may  be  dissolved  completely  ;  and,  on 
the  other,  that  the  plate  of  gold  may  remain  whole  after 
the  operation.  The  following  is  that  which  experience  has 
proved  best.  The  quantity  of  matter  operated  upon,  or 
taken  for  the  assay,  should  be  about  12  grains,  and  the 
alloys  resulting  from  these  12  grains,  and  the  silver  em- 

*  Pettenkoffer  and  others  have  shown  that  less  than  two  parts  of  silver  will 
suffice,  and  be  even  advantageous. 


THE    OPERATION   OF    DfQUARTATION.  68tf 

ployed  in  the  inquartation,  should  be  made  into  a  plate  of 
from  18  to  20  lines  in  length  and  4  or  5  in  breadth. 

The  cornet  for  assay  is  placed  in  a  glass  matrass, 
capable  of  containing  about  three  ounces  of  water ;  pure 
nitric  acid  is  added  at  different  times,  and  heat  applied. 
When  all  the  silver  is  dissolved,  it  is  washed  by  decant a- 
tion  with  water  ;  the  matrass  is  reversed  into  a  small 
crucible,  the  cornet  falls  out  and  is  dried.  In  this  state 
the  cornet  is  very  fragile,  and  of  a  dull  red  colour ;  it  is 
annealed  in  a  muffle,  and  heated  gradually  without  fusion. 
It  becomes  thereby  much  contracted,  and  acquires  a 
metallic  lustre,  and  so  much  solidity  that  it  can  be  weighed 
without  fear  of  breaking  it.  Its  weight  can  be  ascertained 
in  the  assay  balance. 

There  are  many  ways  of  employing  nitric  acid.  For- 
merly 2.^  ounces '(thirty-five  times  the  weight  of  the  alloy) 
of  nitric  acid  (1-15  sp.  gr.)  was  poured  upon  the  inquar- 
tated  cornet,  and  boiled  gently  for  fifteen  or  twenty 
minutes,  the  liquid  decanted  and  replaced  by  1  ^  of  acid 
(1-24  or  1'26),  twenty-four  times  the  weight  of  the  alloy, 
boiling  for  twelve  minutes,  then  decanting  and  washing, 
&c.  Vauquelain  advised,  in  his  '  Manuel  de  1'Essayeur,' 
to  pour  on  the  quartated  cornet — the  weight  of  the  assay 
being  7*7  grains — 554  to  770  grains  of  nitric  acid  (1*16 
sp.  gr.),  which  ought  to  fill  the  matrass  half  or  two-thirds, 
and  boil  gently  for  twenty,  or  twenty-two  minutes  at  most, 
to  decant  and  replace  the  liquid  by  500  to  800  grains  of 
acid  (1-26  sp.  gr.),  and  to  boil  for  eight  or  ten  minutes.  The 
assay  is  to  be  acted  on  always  twice,  because  if  we  employ 
at  once  very  strong  acid,  the  action  will  be  too  brisk,  and 
the  cornet  might  be  broken  or  carried  out  of  the  matrass, 
and,  on  the  other  side,  the  acid  of  T16  sp.  gr.  cannot  dis- 
solve the  last  portions  of  silver,  which  are  very  difficult  to 
separate  from  the  gold. 

Surcharge. —  It  is  remarked  that  by  following  this 
method  the  cornet  always  retains  a  small  quantity  of  silver, 
so  that  fine  gold  submitted  to  quartation  and  parting 
always  weighs  more  after  than  before  the  operation.  The 
augmentation  of  weight  which  it  undergoes  is  termed  the 


686  THE   ASSAY   OF   GOLD 

surcharge-,  this  surcharge  is  commonly  from  O'OOl  to 
0-002.  M.  Chaudet  has  found  means  to  avoid  it.  In  order 
to  do  so,  pour  on  to  the  quartated  cornet  nitric  acid  of 
1-16  sp.  gr.,  and  heat  for  three  or  four  minutes  only;  re- 
place this  acid  by  acid  of  1'26  sp.  gr.,  and  boil  during  ten 
minutes  ;  decant  and  make  a  second  boiling  with  acid  of 
1-26  sp.  gr:,  which  boil  for  eight  or  ten  minutes.  The 
assay  requires  but  from  twenty  to  twenty-three  minutes, 
and,  according  to  M.  Chaudet,  gives  perfectly  pure 
gold. 

A  source  of  loss  occurs  in  parting  operations  and  refin- 
ing on  the  large  scale,  from  the  solution  of  gold  in  nitric 
acid,  even  when  it  is  quite  free  from  hydrochloric  acid,  in 
consequence  of  the  formation  of  nitrous  acid.  To  ascer- 
tain the  amount  of  loss  from  this  source  in  ordinary  assay 
operations,  Mr.  Makin  took  four  specimens  of  pure  gold 
accurately  weighed,  added  the  usual  proportions  of  fine 
silver  and  lead,  and  then  cupelled  them.  The  resulting 
buttons  were  rolled,  coiled,  and  parted  with  nitric  acid, 
the  cornets  being  boiled  in  two  acids  of  different  strengths 
a  different  number  of  times.  Calling  the  weighings  before 
the  operation  1000,  the  results  were  as  follows  : — 

1.  Boiled  in  acid  twice 999-6 

2.  „  three  times  .         .         .         .         .         .     999'2 

3.  „  four      „       .        -,-    •  .    l    .         .         .     9987 

4.  „  five       „       .        .     ,....,;*. r.,    ,        .     997-9 

The  loss  is  thus  seen  to  increase  as  the  boilings  are  multi- 
plied. 

When  silver  is  present  in  large  quantity,  Mr.  Makin 
believes  that  the  solvent  action  of  nitrous  acid  is  restrained 
by  electrical  action,  the  gold  becoming  the  negative  and 
the  silver  the  positive  pole  of  a  circuit ;  but  as  the  silver  is 
removed,  the  solution  of  the  gold  goes  on  more  rapidly. 
The  cause  of  the  evolution  of  nitrous  acid  is  evident  as  long 
as  there  is  any  silver  present,  and  it  often  results  from  the 
use  of  charcoal  to  prevent  '  bumping.'  When  charcoal 
is  thoroughly  carbonised,  it  does  not  materially  affect  the 
acid  ;  but  if  it  contain  woody  matter,  nitrous  acid  is  sure  to 


METHOD    OF   MAKIX.  687 

be  set  free.  Mr.  Makin  has  given  up  the  use  of  charcoal 
on  this  account. 

The  commercial  importance  of  this  subject  will  be  ad- 
mitted, when  we  remember  the  enormous  value  of  the 
metals  dealt  with  in  this  country,  and  that  the  question  of 
profit  and  loss  in  commercial  transactions  with  them  are 
almost  entirely  in  the  hands  of  the  assay er.  A  knowledge 
of  these  facts  may  also  ser^e  to  account  for  some  of  the 
discrepancies  between  assayers. 

In  the  assay  of  auriferous  ores,  the  button  produced 
by  cupellation  commonly  contains  silver.  When  the  pro- 
portion of  this  metal  surpasses  that  of  inquartation,  the 
button  is  flattened  between  two  pieces  of  paper,  and  treated 
by  pure  nitric  acid.  The  gold  remains  under  the  form  of 
a  yellowish-brown  powder,  which  is  weighed  immediately, 
or  fused  in  the  cupel  enveloped  in  a  sheet  of  lead.  When 
the  quantity  is  extremely  small  and  imponderable,  we  can 
assure  ourselves  at  least  of  its  presence  by  treating  the 
residue  left  by  nitric  acid  with  aqua  regia ;  if  it  contain 
gold,  it  dissolves  and  gives  a  yellowish  liquid,  in  which  a 
drop  of  solution  of  chloride  of  tin  or  the  crystallised  chloride 
forms  a  deposit  of  purple  of  Cassius  of  a  violet  colour  : 
this  character  proves  the  presence  of  the  smallest  traces 
of  gold.  When  the  gold  predominates  in  the  button,  it  is 
necessary  to  re-fuse  it  with  three  times  or  less  its  weight  of 
silver,  and  recommence  the  assay  with  the  addition  of  this 
preparation  of  silver. 

Aqua  Regia. — When  gold  is  the  largest  portion  of  the 
alloy,  and  when  there  are  reasons  for  not  adding  silver, 
the  parting  can  be  made  by  aqua  regia.  In  this  case,  all 
the  gold  is  dissolved,  and  the  silver  converted  into  chloride  ; 
the  chloride  is  washed,  dried  perfectly,  and  weighed.  When 
the  gold  is  precipitated  by  ferrous  sulphate,  it  is  washed 
with  a  little  hydrochloric  acid,  and  annealed  strongly  be- 
fore weighing,  or  even  annealed  so  far  as  to  fuse  it,  and 
then  cupelled  with  lead. 

If  an  alloy,  containing  much  silver,  be  treated  by  this 
process,  it  sometimes  happens  that  the  excess  of  silver 
chloride  prevents  the  complete  solution  of  the  gold.  In 


688  THE   ASSAY   OF   GOLD. 

this  case  it  is  necessary  to  reduce  the  alloy  to  an  exces- 
sively thin  plate,  to  dissolve  the  chloride  in  ammonia,  and 
to  treat  afresh  with  aqua  regia.  This  process  can  rarely 
be  made  use  of  on  the  large  scale,  because  the  precipitation 
of  gold  by  ferrous  sulphate  is  long  and  troublesome. 

M.  G.  Rose  fuses  the  alloy  with  lead,  over  a  spirit- 
lamp,  in  a  porcelain  crucible,  acts  on  it  with  nitric  acid, 
which  dissolves  the  silver  and  lead,  precipitates  the  silver 
by  a  solution  of  lead  chloride  ;  lastly,  the  auriferous 
residue  is  dissolved  by  aqua  regia ,  and  the  gold  precipitated 
by  ferrous  chloride. 

For  the  separation  of  gold  and  silver  and  their  deter- 
mination in  alloys,  H.  von  Jtiptner  ('  Zeitschrift  flir  Analy- 
tische  Chemie,'  1879,  105)  alloys  the  metal  with  5  to  8 
parts  of  zinc,  and  dissolves  in  nitric  acid  ;  zinc,  silver, 
copper,  &c.,  dissolve,  whilst  gold  and  the  platinum  metals 
remain,  and  also  tin  as  oxide,  if  present.  The  zinc  alloy  is 
easily  found,  and  the  metals  in  the  crucible  are  best  covered 
with  resin  to  prevent  oxidation. 

If  it  is  known  that  neither  tin  nor  platinum  is  present, 
it  is  sufficient  to  decant,  dry,  and  weigh  in  order  to  find  the 
weight  of  the  gold. 

If  the  platinum  metals  or  tin  are  suspected  the  residue 
is  dissolved  in  aqua  regia ,  the  free  chlorine  is  expelled  by 
boiling,  the  gold  is  reduced  with  ferrous  ammonium  sul- 
phate of  known  strength,  and  the  excess  of  ferrous  oxide 
titrated  with  potassium  permanganate.  From  the  quantity 
of  ferrous  oxides  consumed  in  the  reduction  of  the  gold  its 
proportion  may  be  calculated. 

All  the  silver  is  contained  in  the  nitric  acid  solution  of 
the  zinc  alloy. 

By  another  method  for  the  separation  of  gold  and  silver 
the  metal  is  alloyed  with  5  to  8  parts  of  zinc,  for  which 
the  heat  of  a  Bunsen  burner  is  sufficient.  The  alloy  is 
dissolved  in  nitric  acid,  when  gold  (with  platinum  and  tin 
as  stannic  oxide,  if  present)  remains  undissolved.  To 
separate  gold  from  platinum  and  tin  they  are  dissolved  in 
aqua  regia,  the  platinum  metals  are  precipitated  with  am- 
monia, the  free  chlorine  is  expelled,  and  the  liquid  is  mixed 


ASSAY   OF   GOLD    COIN   AND   BULLION. 


689 


with  excess  of  ammonio-ferrous  sulphate,  the  excess  of 
which  is  determined  by  titrating  back  with  permanganate 
('  Zeitsehrift  fur  Anal.  Chemie,'  18, 104). 

Standard  of  the  Alloys  of  Gold. — The  real  standard 
of  the  alloys  of  gold  is  expressed  in  fractions  of  unity,  as  in 
the  case  of  alloys  of  silver.  We  suppose  24  carats  in  unity, 
and  32-32nds  in  the  carat ;  the  unity  contains  then 
768-32nds.  After  these  data  the  following  table  has  been 
formed,  which  expresses  the  relation  of  32nds  and  carats  to 
decimal  fractions  of  the  unity  : — 


32nds 
1 

2 

3 

4 

5 

6 

7 

8 

9 

10 
11 
12 
13 
14 
15 
16 
17 
18 
19 
20 
21 
22 
23 
24 
25 
26 
27 
28 
29 
30 
31 
32 


Decimals 

Carats 

0-001302 

1 

0-002604 

2 

0-003906 

3 

0-005208 

4 

0-006510 

5 

0-007912 

6 

0-009115 

7 

0-010415 

8 

0-011718 

9 

0-013021 

10 

0-014323 

11 

0-015625 

12 

0-016927 

13 

0-018230 

14 

0-019531 

15 

0-020833 

16 

0-022135 

17 

0-023436 

18 

0-024740 

19 

0-026042 

20 

0-027343 

21 

0-028644 

22 

0-029948 

23 

0-031250 

24 

0-032552 

0-033854 

0-035156 

0-036460 

0-037760 

0-039062 

0-040364 

0-041667 

Decimals 

0-041667 
0-083334 
0-125001 
0-166667 
0-208333 
0-250000 
0-291666 
0-333333 
0-374999 
0-416667 
0-458630 
0-500000 
0-541667 
0-583333 
0-624555 
0-666667 
0-707333 
0-750000 
0-791666 
0-833333 
0-874999 
0-916666 
0-958333 
1-000000 


Assays  of  Gold  Coin  and  Bullion  (Alloys  of  Gold  and 
Copper ',  or  Gold,  Silver ',  and  Copper). 

Preliminary  Assay. — As  in  the  case  of  silver  assaying 
the  quantity  of  lead  to  be  employed  is  of  importance,  a 
preliminary  assay  must  be  made  when  the  standard  of  the 

Y  Y 


690  THE   ASSAY   OF    GOLD, 

alloy  to  be  examined  is  not  approximatively  known.  It  is 
thus  effected : — To  2  grains  of  the  alloy  add  6  grains  of 
fine  silver  and  50  grains  of  pure  lead.  The  lead  must  be 
introduced  into  a  hot  cupel,  and  when  fused,  and  its  sur- 
face fully  uncovered,  the  alloy  and  silver  may  be  addedy 
wrapped  either  in  thin  paper  or  a  small  quantity  of  lead 
foil.  The  cupellation  finished,  and  the  cupel  cold,  the 
button  of  gold  and  silver  must  be  removed  from  the  cupel 
by  aid  of  the  pliers,  and  if  necessary  cleansed.  Hammer  it 
to  a  thin  plate  on  the  anvil,  place  it  in  a  small  evaporating 
basin,  and  treat  it  with  half  an  ounce  of  nitric  acid.  (It 
may  be  here  mentioned,  that  the  nitric  acid  employed  in  the 
assay  of  gold  must  be  chemically  pure,  and  special  care 
must  be  taken  that  it  contains  no  trace  of  chlorine.)  The 
evaporating  basin  is  gently  heated  until  all  action  ceases. 
The  brownish  residue  is  repeatedly  washed  with  hot  water, 
dried,  ignited,  and  weighed  ;  and  from  its  weight  the 
amount  of  lead  and  silver  to  be  added  in  the  actual  assay 
may  be  determined.  The  presence  of  copper  in  the  alloy 
is  indicated  by  the  blackness  of  the  cupel  where  it  is  satu- 
rated with  oxide. 

Assay  Proper. — In  this  case  it  will  be  supposed  that 
standard  gold  is  the  alloy  operated  on,  and  that  prelimi- 
nary assay  has  given  about  91^  per  cent,  of  gold.  On 
referring  to  the  table  (page  681),  it  will  be  found  that 
between  27  and  30  parts  of  lead  are  required  for  such  per- 
centage of  gold,  and  that,  according  to  the  general  observa- 
tions on  this  class  of  assay,  three  times  its  weight  (that  is, 
the  weight  of  fine  silver)  will  be  required  to  so  dilute  the 
gold  that  nitric  acid  can  attack  and  dissolve  out  the  whole 
of  the  silver  combined  with  it. 

Place  the  weight  representing  24  carats  in  the  pan  of 
the  balance,  and  exactly  counterpoise  it  with  the  gold  to  be 
assayed  ;  two  portions  should  be  thus  weighed.  Two  por- 
tions of  fine  silver  must  now  be  weighed  ;  33  grains  will  be 
required  for  each  24  carats  of  gold,  as  22  carats,  or  11 
grains,  of  fine  gold  exist  in  the  24  carats,  and  three  times 
the  quantity  of  silver  is  necessary.  300  grains  of  lead  must 
be  placed  in  a  hot  cupel  (two  being  thus  prepared),  and,  as 


ASSAY   OF   ALLOYS    (ASSAY   PROPER).  691 

in  the  preliminary  assay,  when  the  surface  is  fully  uncovered, 
the  gold  and  silver  are  added,  and  the  cupellation  proceeded 
with,  taking  all  the  precautions  already  fully  pointed  out 
elsewhere. 

The  button  so  obtained  is  cleaned,  hammered  on  the 
anvil,  then  annealed  and  passed  between  the  rollers  of  a 
small  flatting-mill ;  being  occasionally  annealed,  in  order  to 
prevent  the  laminated  button  cracking  at  the  edges.  When 
reduced  to  the  desired  degree  of  thinness  it  is  again  an- 
nealed and  rolled  round  a  quill  or  glass  rod  into  a  spiral, 
termed  a  cornet.  This  cornet  is  placed  in  a  parting  flask 
with  li  oz.  of  nitric  acid,  sp.  gr.  1-16,  very  gently  heated 
to  the  boiling  point,  and  at  that  maintained  for  ten  minutes. 
The  acid  is  then  to  be  poured  off,  and  2  oz.  of  nitric  acid, 
sp.  gr.  1*26,  added,  and  again  boiled  for  ten  minutes.  This 
second  acid  is  also  poured  off,  and  a  third  quantity  of  like 
specific  gravity  added  and  boiled.  The  cornet  is  then  well 
washed  with  distilled  water,  and  the  flask,  filled  with  dis- 
tilled water,  is  inverted,  having  its  mouth  closed  with  the 
thumb.  The  cornet  will  fall  through  the  water  without 
breaking,  and  can  be  introduced,  together  with  some  of  the 
water,  into  a  small  crucible  (cornet  crucible),  the  water 
poured  off,  the  crucible  and  gold  gradually  dried,  and  then 
heated  to  redness.  When  cold,  the  final  operation  of 
weighing  may  be  performed,  thus  : — The  weight  represent- 
ing 22  carats  is  placed  in  one  pan  of  the  balance,  and  the 
cornet  in  the  other  :  as  the  gold  employed  was  supposed  to 
be  standard,  it  ought  to  weigh  exactly  22  carats.  If,  how- 
ever, gold  of  greater  or  less  fineness  had  been  submitted  to 
assay — say  of  23  and  21  carats  respectively — 1  carat  weight 
would  have  been  required  in  the  pan  containing  the  22- 
carat  weight,  to  counterbalance  the  gold  carat :  in  this  case 
the  gold  would  be  23  carats  fine,  or,  in  the  usual  mode  of 
reporting,  *  one  carat  better.'  If,  on  the  other  hand,  the  1 
carat  weight  had  been  found  necessary  in  the  pan  containing 
the  cornet,  the  gold  would  be  21  carats  fine,  or  '  one  carat 
worse/ 

In  cases  where  it  is  known  that  the  gold  under  exami- 
nation contains  no  silver,  the  only  alloy  being  copper,  its 

Y    Y  2 


692  THE   ASSAY   OF   GOLD* 

fineness  can  be  determined  by  cupelling  24  carats  with  its 
proper  portion  of  lead,  and  weighing  the  resulting  button, 
which  should  represent  the  amount  of  fine  gold  in  the  alloy 
assayed. 

Parting  Assays. — Parting  assays  are  those  assays  by 
which  the  amount  of  fine  gold  and  fine  silver  in  any  alloy  is 
determined.  When  the  amount  of  gold  exceeds  that  of  the 
silver,  it  is  called  '  gold  parting ; '  when  the  amount  of 
silver  exceeds  that  of  the  gold,  '  silver  parting.' 

In  this  assay  the  weights  employed  in  the  silver  assay 
are  employed,  as  the  report  is  made  in  ounces  of  fine  metal 
per  pound  Troy. 

12  grains  (representing  1  Ib.  Troy)  of  the  alloy  are 
weighed  off,  cupelled  with  300  grains  of  lead,  and  the 
resulting  button,  containing  only  gold  and  silver,  is  weighed. 
Suppose  it  weigh  10  grains,  then  2  grains,  =  2  ounces  in 
the  pound  of  alloy,  is  copper  or  some  other  metal,  which 
has  been  oxidised  and  carried  into  the  cupel  with  the 
litharge.  A  preliminary  assay  must  be  made  of  the  alloy, 
to  ascertain  the  approximative  quantity  of  silver  and  gold, 
so  as  to  apportion  the  amount  of  silver  in  the  assay  proper  : 
this  amount  being  found,  it  is  to  be  weighed  off,  added  to 
the  button  of  fine  gold  and  silver  obtained  as  above,  and 
the  whole  cupelled  with  200  grains  of  lead  ;  the  cupelled 
mass  of  gold  and  silver  laminated  and  treated  with  nitric 
acid,  as  already  described,  and  the  resulting  gold  weighed. 
Suppose  the  weight  to  be  8  grains,  =  8  ounces,  the  result 
would  stand  thus  : — 


Copper  or  other  base  metal  .    .  •  .  •  0  •»         .     2  oz. 

Gold '\*  '•'  .        .    8  „ 

Silver.        .  -• ,  v •'•  .>f  ,-:>  j-  =  .-*:::.--. •?-•      .    2,, 

12  oz. 

The  above  arrangement  is  very  convenient  for  accom- 
plishing gold  assays,  and  is  the  one  employed  in  the  assay 
office  of  the  French  Mint.  The  annexed  cut  (fig.  130) 
represents  this  apparatus. 

The  assay  flask,  M,  being  charged  with  the  cornet,  a 
constant  amount  of  acid  is  added  with  a  pipette.     On  the 


PARTING   ASSAYS  693 

addition  of  the  second  acid  a  small  piece  oi  charcoal  is 
placed  in  the  flask  :  this  serves  to  prevent  bumping  during 
ebullition.  The  flasks  are  supported  on  a  plate  of  sheet 
iron,  P,  pierced  with  holes  or  by  a  grating,  and  the  acid 
vapours,  before  escaping  by  the  flue,  pass  into  glass  tubes, 
7T,  about  half  an  inch  in  diameter,  and  four  feet  long  :  at 
each  end  a  narrower  tube,  t,  is  fused.  The  lower  tube 

FIG.  130. 


freely  enters  the  neck  of  the  flask  ;  and  as  the  space 
between  is  so  small  that  a  layer  of  acid  remains  suspended 
and  obstructs  the  passage  of  the  acid  vapours,  they  are 
thus  forced  to  pass  into  the  large  tube,  where,  for  the 
greater  part,  they  condense  and  fall  into  the  flasks.  By 
this  means  the  quantity  of  acid  employed  in  the  assay  can 
be  diminished,  as  there  is  no  loss  by  evaporation,  and  the 


694  THE    ASSAY   OF    GOLD. 

results  are  found  to  be  more  constant.  In  order  that  the 
passage  to  the  large  tube  for  the  acid  vapours  may  always 
remain  free,  the  end  of  the  narrow  tube  passing  into  the 
flask  must  be  cut  at  an  angle  (see  P).  The  drops  of  acid 
collect  at  this  part,  and  never  close  the  tube. 

Assay  of  Pyrites  for  Gold. 

Mr.  J.  M.  Merrick  gives  the  following  method  for 
assaying  pyrites  for  gold  : — 

*  One  pound,  or  even  18  ounces  (avoirdupois),  of  fine 
marble-dust  is  mixed  with  8  ounces  of  finely  pulverised 
and  sifted  pyrites ;  the  whole  then  re-sifted  and  put  into 
a  Hessian  crucible,  which  should  be  about  one-third  filled 
by  the  mixture.  The  crucible  is  set  as  usual  on  a  fire- 
brick, and  a  fire  of  hard  coal  is  made  around  it,  the  coals 
being  heaped  up  to  within  an  inch  of  the  top.  The  cru- 
cible is  covered  with  a  piece  of  brick  or  a  piece  of  sheet 
iron.  During  the  first  half-hour  the  contents  should  be 
stirred  once  or  twice.  As  the  fire  grows  brisker  the  car- 
bonic acid  evolved  keeps  the  contents  of  the  crucible  in 
brisk  ebullition,  and  the  mixture  should  be  stirred  well 
every  5  or  10  minutes.  On  stirring  during  this  time,  the 
iron  rod  used  seems  to  meet  with  but  little  resistance 
from  the  light  mass,  but  at  the  end  of  about  1^  hours  the 
evolution  of  gas  suddenly  ceases,  the  red-hot  mass  becomes 
heavy,  sinks,  and  requires  considerable  force  to  keep  it 
stirred.  It  must  be  stirred  well  and  vigorously,  however, 
for  about  half  an  hour,  not  leaving  it  unstirred  for  more 
than  a  minute,  otherwise  the  mass  will  fuse  or  cake,  and 
the  assay  will  be  almost  inevitably  ruined. 

'  When  a  sample  taken  out  in  an  iron  spoon  gives  off 
no  smell  of  sulphur,  the  entire  contents  of  the  crucible 
must  be  turned  into  a  stoneware  pot  or  a  wooden  bucket 
half  filled  with  water,  and  well  stirred.  When  the  powder 
— which  should  be  uniform  and  free  from  lumps  or  fused 
pieces — has  settled,  the  water  must  be  poured  off,  the 
wet  mass  allowed  to  drain,  and  then  transferred  to  a  large 
earthen  bowl  or  porcelain  mortar.  Here  it  is  to  be  amal- 


ASSAY.   OF   PYEITES   FOR   GOLD.  695 

gamated  with  about  2  ounces  of  mercury,  to  which  a  little 
bit  of  sodium  amalgam  has  been  added.  The  amalgama- 
tion, as  well  as  the  stirring  in  the  fire,  is  a  tedious  process, 
and  one  which  it  is  as  well  to  do  by  proxy.  It  does  not 
consist  in  merely  grinding  with  a  pestle  the  mercury  in 
among  the  particles  of  the  roasted  ore,  but  this  ore  itself 
must  be  ground  in  contact  with  the  mercury,  until  the 
particles  are  so  fine  that  they  will  float  suspended  in  water 
for  several  seconds.  At  the  end  of — say — 10  minutes' 
thorough  grinding,  the  contents  of  the  bowl  are  to  be 
brought  into  one  mass  in  the  bottom  of  the  vessel,  the 
bowl  then  sunk  in  a  tub  of  water,  and  the  contents 
"  washed  down  " — an  operation  not  easily  described,  but 
familiar  enough  to  every  old  Californian.  It  consists 
essentially  in  shaking  the  bowl  half  full  of  ore  and  water 
in  such  a  way  that  the  mercury,  gold  particles,  and  un- 
ground  ore  sink  to  the  bottom,  while  the  light  and 
finely-ground  ore,  is  floated  off  into  the  tub.  The  ore 
remaining  is  re-ground  and  re-washed,  and  these  processes 
are  repeated  till  nothing  but  the  mercury  remains  in  the 
bottom  of  the  bowl  or  mortar.  This  mercury  is  then 
dried  with  filter-paper,  and  heated  in  a  porcelain  capsule 
over  a  Bunsen  flame,  very  gently,  until  it  is  sublimed  and 
the  gold  remains  behind.  The  film  of  gold  may  then  be 
scraped  up  and  melted,  with  a.  little  borax  and  nitre,  in 
the  very  smallest-sized  Hessian  crucible,  either  with  the 
foot  blowpipe  or  in  a  charcoal  furnace,  by  which  means  a 
round,  clean  button  of  gold,  suitable  for  weighing,  will  be 
obtained. 

4  This  method  has  its  disadvantages  and  its  counter- 
balancing merits.  On  the  one  hand,  it  must  be  admitted 
to  be  tedious,  laborious,  and  to  a  considerable  degree 
uncertain.  Some  analysts  fail  with  it  altogether,  while 
none  who  have  tried  it,  so  far  as  I  know,  get  closely 
agreeing  results. 

'  But,  on  the  other  side,  it  is  as  certain  that  this 
method  will  indicate  the  presence  of  gold,  and  will  bring 
out  the  gold  in  a  weighable  form  from  pyritic  ores,  where 
the  assay  by  smelting  will  not  show  a  remote  trace  of  the 


69(>  THE   ASSAY   OF    GOLD. 

precious  metal  ;  and  that  where  the  fire  assay  shows  a 
certain  percentage  this  will  invariably  bring  out  a  larger 
amount.  Large  returns  have  been  obtained  by  this 
amalgamation  method  from  iron  pyritic  ores,  which  have 
been  repeatedly  assayed  in  the  ordinary  way,  by  chemists 
of  great  eminence,  with  uniformly  negative  results.' 

Detection  of  Minute  Traces  of  Gold  in  Minerals. — Mr. 
Skey,  analyst  to  the  Geological  Survey  of  New  Zealand, 
has  devised  a  plan  which  gives  very  good  results,  even 
when  small  quantities  of  mineral  are  operated  on.  He 
employs  iodine  or  bromine  for  the  purpose  of  dissolving 
out  the  gold.  Both  of  these  substances  differ  from  chlo- 
rine especially  in  their  relatively  feeble  affinities  for  hydro- 
gen, so  that  there  is  less  fear  that  from  the  generation 
of  hydrogen  acids  any  great  preponderance  of  other 
matters  would  be  dissolved  along  with  the  gold.  Either 
of  these  substances  can  be  safely  and  advantageously 
employed  for  the  separation  of  gold  from  its  matrix. 

The  following  particulars  of  experiments  made  by  this 
method  will  be  useful  in  showing  what  is  approximately 
the  smallest  quantity  of  gold  that  can  be  positively  sepa- 
rated and  identified  when  operating  upon  a  limited 
quantity. 

1st.  2  grms.  of  roasted  '  buddle  headings '  from  a 
quartz  mine  at  the  Thames,  N.Z.,  known  to  contain  gold 
at  the  rate  of  1  oz.  or  so  to  the  ton,  was  well  shaken  for  a 
little  while  with  its  volume  of  alcoholic  solution  of  iodine, 
then  allowed  to  subside.  A  piece  of  Swedish  filter-paper 
was  then  saturated  with  the  clear  supernatant  liquid,  and 
afterwards  burned  to  an  ash  ;  the  ash,  in  the  place  of 
being  white,  as  it  would  be  if  pure,  was  coloured  purple  ; 
the  colouring  matter  was  quickly  removed  by  bromine — 
a  clear  indication  of  the  presence  of  gold.  The  time 
occupied  by  the  whole  process  was  twenty  minutes. 

2nd.  1  grm.  of  the  same  'buddle  headings,'  mixed 
with  such  a  quantity  of  earth  as  to  reduce  the  proportion 
of  gold  present  to  2  dwt.  per  ton,  was  kept  in  contact 
with  its  own  volume  of  the  tincture  of  iodine  for  two 
hours,  with  occasional  stirring  ;  a  piece  of  filter-paper  was 


DETECTION   OF   GOLD   IN   MINERALS.  697 

then  saturated  with  the  liquid,  and  dried,  five  times  con- 
secutively, and  finally  burnt  off  as  before  ;  in  this  case,, 
also,  the  colour  of  the  residual  ash  was  purple,  and  it 
gave  the  reaction  of  gold. 

3rd.  32  grms.  of  siliceous  hematite,  finely-pounded ,. 
were  thoroughly  mixed  with  precipitated  gold  to  the 
amount  of  2  dwts.  per  ton  ;  then  ignited  and  treated  with 
bromine  water.  After  two  hours  the  solution  was  filtered,, 
and  evaporated  to  a  bulk  of  20  minims  ;  this  gave  a  good 
reaction  of  gold  to  the  '  tin  chloride '  test. 

4th.  100  grms.  of  the  hematite,  with  precipitated  gold 
at  the  rate  of  ^  dwt.  per  ton,  treated  as  before,  but  thi& 
time  well  washed  at  the  expiration  of  two  hours ;  the 
washings  evaporated  along  with  the  first  filtrate,  gave 
a  fainter,  but  still  decided,  reaction  of  gold  to  the  same 
test. 

5th.  Iodine,  as  tincture,  substituted  for  bromine  in 
Experiments  3  and  4,  gave  similar  results ;  the  only  varia- 
tion made  was,  that,  as  a  precautionary  measure  allowing 
for  its  slower  action,  they  were  kept  in  contact  for  twelve 
hours. 

Careful  experiments  have  been  made  to  compare  the 
results  of  the  common  amalgamating  process  with  the 
foregoing,  and  it  has  been  found  that  it  is  not  certain, 
with  the  same  expenditure  of  labour,  to  get  reliable  indi- 
cations of  gold,  when  present  in  less  quantity  than  2  dwt. 
per  ton,  operating  upon  about  100  grms.  of  material. 

In  summing  up  the  results  of  these  experiments,  it 
appears,  then,  that  for  qualitative  examinations  for  gold, 
or  for  quantitative  determinations  in  certain  cases,  iodine 
and  bromine  are  each  superior  to  mercury.  It  also  appears 
that  a  proportion  of  gold  equal  to  i  dwt.  per  ton,  upon  a 
bulk  of  about  4  ozs.  of  ferruginous  matters,  can  be  easily 
and  rapidly  detected.  Of  course,  by  operating  upon 
larger  bulks,  gold  could  be  discovered  by  this  process, 
were  it  present  in  far  less  quantities,  but  this  is  sufficiently 
near  for  the  majority  of  cases. 

These  processes  are  especially  adapted  for  the  sepa- 
ration of  gold  from  sulphides,  as  the  preliminary  roasting 


698  THE   ASSAY   OF   GOLD. 

is  extremely  favourable  to  them,  the  loss  in  the  substitu- 
tion of  oxygen  for  sulphur  amounting  to  25  per  cent,  by 
weight,  while  the  volume  remains  constant  (or  nearly  so) ; 
hence  there  is  a  corresponding  porosity  in  the  product, 
by  which  every  particle  of  it  is  thrown  open  to  contact 
with  the  solution.  This  mechanical  accessibility  obviously 
cannot  be  taken  advantage  of  by  mercury. 

With  sulphides  these  processes  are  practically  ex- 
haustive, while,  at  the  same  time,  the  simultaneous  extrac- 
tion of  other  matters  is  so  trifling,  that  the  proper  tests 
for  gold  can  be  safely  applied  directly  to  the  concentrated 
solution.  In  the  roasting  of  pyrites  it  is  necessary  to 
raise  the  temperature  towards  the  end  to  a  full  red  heat, 
in  order  to  decompose  the  ferruginous  sulphates,  since  if 
these  remained  iron  would  get  into  the  solution.  In  the 
case  of- an  excess  of  calcium  carbonate  being  present,  it  is 
proper  to  gently  re-ignite  the  roasted  mineral,  &c.,  with 
ammonium  carbonate,  or  much  lime  might  get  into  the 
iodine  or  bromine  solution.  On  the  other  hand,  a  very 
high  temperature  is  to  be  avoided,  for  a  considerable 
quantity  of  fine  gold  can  escape  detection  in  this  way, 
by  the  partial  vitrification  of  the  more  fusible  of  the 
silicates. 

The  identification  of  gold  by  the  combustion  of  its 
salts  with  filter-paper  seems  to  promise  a  raipd  method  of 
estimating  it,  comparatively,  by  the  aid  of  a  series  of  pre- 
pared test-papers,  representing  gold  in  different  degrees  of 
dilution. 

It  seemed  at  one  time  possible  that  the  assay  of  silver 
alloys  might  be  simply  and  rapidly  effected  by  the  aid  of 
the  spectroscope.  The  researches  of  Professor  Chandler 
Eoberts,  F.E.S.,  Chemist  to  the  Mint,  and  of  Mr.  A.  E. 
Outerbridge,  Assistant  in  the  Assay  Department  of  the 
United  States  Mint,  show  that  for  the  present  at  least  these 
expectations  are  groundless. 

It  has  been  shown  by  Mr.  Capel  that  the  4  ^  0  of  a 
milligramme  of  gold  will  show  a  spectrum,  if  the  spark  be 
passed  through  a  weak  solution  of  the  pure  metal.  But 
when  operating  on  a  slip  of  alloy  formed  of — 


DETECTION   OF   GOLD    IN   MINERALS.  699 

Silver     .        .      '>,'.'       1     "   .        .    708 
Copper  .......     254 

Gold      .  38 

1000 

the  spectra  of  copper  and  silver  alone  were  visible.  In 
an  alloy  of  gold  and  copper  containing  from  200  to  250 
parts  in  the  thousand  of  the  precious  metal,  the  gold 
spectrum  is  barely  visible.  On  the  other  hand,  in  an 
alloy  of  gold  and  copper  containing  1  per  cent,  of  the 
latter,  the  copper  spectrum  was  distinctly  shown.  In 
copper  alloyed  with  20  per  cent,  of  nickel,  the  spectrum 
of  the  latter  is  not  visible.  Hence  we  arrive  at  the  in- 
teresting fact  that  when  two  or  more  metals  are  present, 
<the  spark  will  to  some  extent  elect  for  its  vehicle  the  one 
which  is  most  rapidly  volatilised. 

It  is  also  not  possible  to  obtain  alloys  of  gold  so  per- 
fectly homogeneous  that  the  quantity  of  metal  volatilised 
and  giving  the  spectrum  may  safely  represent  the  whole 
melt. 


700 


CHAPTEE  XVIII. 

THE   ASSAY   OF   PLATINUM. 

PLATHTCTM  is  found  in  a  native  or  metallic  state.  It  occurs 
very  rarely,  yet  it  is  exceedingly  probable  that  wherever 
gold  is  found  this  metal  will  more  or  less  accompany  it. 

It  is  found  disseminated  in  sand,  in  the  form  of  grains 
varying  in  size  from  gunpowder  to  hempseed  :  this  last 
size  they  rarely  exceed,  yet,  as  in  the  case  of  gold,  nuggets 
have  been  found  of  large  size  and  weight.  Its  colour  is 
steel-grey,  or  rather,  a  tinge  between  silver-white  and  steel- 
grey. 

The  sands  from  which  platinum  is  derived  are  remark- 
able, from  the  number  and  importance  of  their  principal 
constituents.  With  the  platinum  may  be  found  Au,  Ag, 
Hg,  Fe,  Cu,  Or,  Ti,  Ir,  Os,  E,  and  Pd.  Besides  all  these 
metals,  precious  stones  have  also  been  found  associated 
with  it. 

The  following  plan  will  serve  to  detect  platinum  ini 
admixture  with  gold  and  other  heavy  matters  obtained  by 
washing  or  vanning  sands,  earths,  &c. 

Act  on  a  small  quantity  by  mercury,  and  separate  the' 
amalgam  ;  by  this  means  the  gold  is  removed.  To  the 
residue  add  aqua  regia  and  boil,  evaporate  the  solution  to 
dryness,  add  a  little  hydrochloric  acid  and  water,  boil  and 
filter.  To  the  filtered  solution  add  a  strong  solution  of  sal 
ammoniac  (ammonium  chloride).  If  a  bright  yellow,  or 
reddish-yellow,  granular  precipitate  falls,  platinum  is* 
present  in  the  sand. 

A  still  more  ready  method  is  the  following : — Separate 
as  much  earthy  matter  as  possible  by  careful  washing.  If 
gold  is  present  separate  that  by  amalgamation.  Dry  the 


ASSAY   OF   PLATINUM   ORES. 


701 


residue  and  take  its  specific  gravity ;  if  it  be  above  10, 
platinum  is  most  likely  present.  The  specific  gravity  of 
native  platinum,  free  from  earthy  matter,  is  from  16  to  19. 

Analysis  of  Platinum  Ores. — The  platinum  sands  often 
contain  metallic  compounds  of  iron  and  platinum,  not  only 
capable  of  being  attracted  by  the  magnet,  but  possessed 
even  of  polarity.  These  grains  have  a  different  composition 
from  those  not  magnetic,  as  shown  in  the  two  following 
analyses  by  Berzelius  : — 

Analysis  of  the  non-magnetic  grains  : — 


Platinum 
Indium  . 
Rhodium 
Palladium 
Iron 
Copper    . 


78-94 

4-97 

•86 

•28 

11-04 

•70 

1-00 

•96 

98-75 


Analysis  of  the  magnetic  grains  : — 


Platinum 
Iridium  . 
Rhodium 
Palladium 
Iron 
Copper    . 
Insoluble  matt 

73-68 
2-35 
1-15 
•30 
12-98 
5-20 
2-30 

srs 

97-86 


These  grains  being  separated,  their  relative  proportion 
is  estimated. 

Bunsen's  method  of  analysing  platinum  ores  is  as  fol- 
lows : — The  ores  employed  contain  no  osmium,  and  were 
relatively  rich  in  rhodium. 

Platinum  and  Palladium. — It  is  easy  to  effect  the 
almost  complete  separation  of  platinum  and  palladium 
from  rhodium,  iridium,  and  ruthenium.  The  original 
material  is  mixed  in  a  Hessian  crucible,  with  from  1  to  ^ 
its  weight  of  ammonium  chloride,  heated  until  the  latter 
is  completely  volatilised,  allowed  to  glow  gently  until  only 
the  vapours  of  ferric  chloride  show  themselves,  and  then 
placed  in  a  porcelain  dish  and  evaporated  to  a  syrupy 


702  THE   ASSAY   OP   PLATINUM. 

consistency,  with  from  two  to  three  times  its  weight  of 
raw  commercial  nitric  acid.  By  this  treatment  with  am- 
monium chloride  the  metals  present  not  belonging  to  the 
platinum  group  will  have  been  partially  converted  to  lower 
chlorides,  the  rhodium,  iridium,  and  ruthenium  will  have 
been  rendered  insoluble,  and  the  silica  present  as  gangue 
converted  from  a  gelatinous  mass  to  a  finely  pulverulent 
condition,  in  which  state  it  will  admit  of  speedy  filtering. 

The  chlorine  compounds,  produced  by  the  ammonium 
chloride,  give,  upon  digestion  with  nitric  acid,  just  enough 
hydrochloric  acid  to  dissolve  the  platinum  to  bichloride , 
while  the  metallic  copper  and  iron  present  act  so  far  re- 
ducingly  upon  the  palladium  (in  solution  in  nitric  acid) 
that  it  remains  in  solution,  not  as  bichloride,  but  as  the 
protochloride,  which  latter  is  not  precipitated  with  potas- 
sium chloride.  The  mass  is  diluted  with  water,  filtered,, 
and  the  solution  saturated  with  potassium  chloride,  and 
the  greater  part  of  the  platinum  separated  pure  as  potas- 
sium platinochloride,  which  is  washed  out  first  with  potas- 
sium chloride,  and  later  with  absolute  alcohol  (the  last 
washings  must  not  be  added  to  the  solution). 

The  filtrate  is  poured  into  a  large  flask  (which  can  be 
made  airtight),  which  will  not  be  more  than  half-filled  with 
it.  Chlorine  gas  is  passed  into  this  flask,  and  it  is  from 
time  to  time  shaken  vigorously,  until  no  further  absorption 
of  gas  takes  place,  when  all  the  palladium  will  have  sepa- 
rated as  a  cinnabar-red  precipitate  of  potassium  palladio- 
chloride  (somewhat  impure,  however,  from  traces  of 
platinum,  iridium,  and  rhodium).  The  fluid  from  which 
these  precipitates  were  obtained  is  now  evaporated,  not 
quite  to  dryness,  with  hydrochloric  acid  ;  and,  upon  ad- 
dition of  just  so  much  water  as  is  necessary  to  dissolve  out 
the  potassium  chloride  and  other  soluble  salts  (aiding  the 
operation  by  rubbing  with  a  pestle),  there  remains  behind 
a  dirty,  yellow-coloured  precipitate.  This  is  separated  by 
filtration,  boiled  with  caustic  soda  and  a  few  drops  of 
alsolute  alcohol.  Hydrochloric  acid  is  added  to  dissolve 
the  precipitate  formed,  and  the  liquid  then  saturated 
with  potassium  chloride ;  the  result  is  a  precipitate  of 


ASSAY   OF   PLATINUM   ORES.  703 

chemically  pure  potassium  platinochloride.  The  mother 
liquid  contains  only  copper  and  no  platinum  metals. 

The  purification  of  the  cinnabar-red  precipitate  of  pal- 
ladium is  accomplished  as  follows  : — Dissolve  in  boiling 
water,  whereby  a  portion  of  the  chloride  dissolves,  with 
evolution  of  chlorine,  to  palladium  protochloride.  Then 
evaporate  with  2^  times  its  weight  of  oxalic  acid,  and  dis- 
solve again  in  a  solution  of  potassium  chloride :  where- 
upon potassium  platinochloride  remains  behind,  chemically 
pure.  Wash  out  as  before. 

The  brown  liquid  is  then  somewhat  concentrated  upon 
the  water-bath  :  and  upon  cooling,  there  separate  bright 
green,  well-formed  crystals  of  potassium  palladio-proto- 
chloride  (with  some  potassium  chloride),  which  upon 
testing,  proves  free  from  the  other  platinum  metals. 

The  fluid  poured  off  from  these  crystals  is  then 
neutralised  carefully  with  caustic  soda,  and  gives  a  slight 
precipitate  of  copper  and  iron,  which  is  filtered  off. 
Upon  adding  potassium  iodide  to  the  filtrate,  all  the 
palladium  separates  as  palladium  iodide.  To  avoid  adding 
an  excess  of  the  reagent,  it  is  best  to  take  from  time  to 
time  a  drop  from  the  fluid  with  a  capillary  tube,  and  put 
the  same  upon  a  watch-glass.  As  long  as  the  precipitation 
is  incomplete,  the  drop  appears,  upon  a  white  background 
brown ;  when  complete,  it  is  colourless ;  when  the  reagent 
is  present  in  excess  it  is  red.  This  is  tested  for  its  purity 
by  reducing  it  to  metallic  palladium,  and  then  heating  and 
dissolving  in  nitric  acid ;  when  pure,  it  must  dissolve 
completely.  The  whole  mass  is  now  reduced  in  a  slow 
stream  of  hydrogen  gas  (whereby  the  iodine  can  be 
obtained  again,  as  hydriodic  acid,  by  absorbing  with 
water).  At  last  the  mass  must  be  strongly  heated,  to 
decompose  slight  traces  of  the  palladium  subiodide  which 
are  formed. 

The  mother  liquid  from  which  all  this  platinum  and 
palladium  have  been  obtained  may  contain  some  iridium 
and  rhodium ;  it  is,  therefore,  evaporated  to  dryness  with 
a  little  potassium  iodide,  whereby  a  mixture  of  rhodium 
and  iridium  iodides  separates.  This  can  either  be  dissolved 


704  THE   ASSAY   OF   PLATINUM. 

in  aqua  regia,  and  the  two  metals  separated  (as  will  here- 
after be  described)  by  sodium  bisulphate,  or  it  can  be 
united  with  the  next  portion  from  which  these  metals  will 
be  obtained. 

Ruthenium,  Rhodium,  and  Iridium. — The  residue  from 
the  original  material  which  remains,  after  treatment  with 
ammonium  chloride  and  nitric  acid,  is  treated  as  follows, 
to  get  the  metals  in  a  form  adapted  to  further  chemical 
treatment. 

The  method  depends  upon  the  behaviour  of  zinc 
chloride  to  zinc.  If  a  piece  of  zinc  be  melted,  it  rapidly 
covers  itself  with  a  stratum  of  oxide.  If,  to  the  melted 
metal,  a  metal  like  iridium  be  added,  the  oxide  stratum 
hinders  the  latter  from  coming  into  contact  with  the  zinc, 
even  though  it  be  pushed  beneath  the  surface.  If,  how- 
ever, a  few  grains  of  ammonium  chloride  be  added  to  it, 
ammonia,  hydrogen,  and  zinc  chloride  will  be  formed, 
which  last  dissolves  the  oxide  stratum  to  basic  zinc  chlo- 
ride. The  zinc  below  resembles  mercury  in  lustre  and 
mobility.  As  soon  as  the  chloride  has  dissolved  as  much 
of  the  oxide  as  is  possible  for  it,  the  oxide  stratum  again 
forms,  and  is  instantly  removed  again  by  the  addition  of 
more  ammonium  chloride.  The  melted  zinc,  strewn  with 
ammonium  chloride,  also  possesses,  like  mercury,  the 
property  of  attacking  other  metals,  if  the  affinity  exists 
of  forming  with  them  alloys.  By  strewing  ammonium 
chloride  upon  the  melted  zinc,  a  quiet  surging  is  kept 
up,  as  the  ammonia  and  hydrogen  are  given  off.  Many 
oxides  and  chlorides  (among  which  are  those  of  the 
platinum  metals),  when  they  come  into  contact  with  this 
atmosphere  of  reducing  gases,  and  with  the  basic  zinc 
chloride,  are  instantly  reduced  and  dissolved  to  alloys  by 
the  zinc.  In  making  the  solution,  the  zinc,  in  a  porcelain 
dish,  should  be  constantly  rotated :  the  gangue  remains 
in  the  basic  chloride.  The  regulus,  immediately  upon 
solidifying,  should  be  taken  from  the  capsule,  out  of  the 
yet  fluid  basic  chloride,  and  washed  off  with  acetic  acid 
until  all  the  basic  chloride  is  dissolved  away.  The  gangue 
can  be  quantitatively  determined  by  filtration  and  weighing 


ASSAY    OF    PLATINUM    ORES.  705 

If  the  regulus  is  not  immediately  removed,  the  containing 
vessel  will  be  broken,  owing  to  the  unequal  expansion 
of  the  porcelain  and  the  metal. 

The  best  proportions  for  a  quantitative  separation  are, 
to  1  part  of  the  platinum  metals,  from  20  to  30  parts  of 
zinc.  For  an  ordinary  separation  7  parts  of  zinc  are 
sufficient. 

For  the  extraction  of  the  residues  remaining  after  the 
treatment  with  nitric  acid,  this  method  is  admirably 
adapted.  By  fusing  only  once  with  zinc  for  two  or  three 
hours,  all  the  platinum  metals  are  extracted.  The  opera- 
tion is  as  follows  : — 

From  3  to  3*5  kilos,  of  commercial  zinc  are  fused  in  a 
2-litre  Hessian  crucible,  ammonium  chloride  from  time 
to  time  strewn  upon  it,  400  grms.  of  residue,  previously 
heated  to  faint  glowing  with  ammonium  chloride,  are 
added,  and  the  temperature  kept,  for  two  or  three  hours, 
just  above  the  fusing  point  of  the  alloy,  by  adding,,  when- 
ever the  mass  threatens  to  solidify,  some  ammonium 
chloride.  The  mass  is  divided  into  three  strata  after 
solidification  has  taken  place. 

The  outer  stratum,  easily  broken  away  by  a  blow  from 
a  hammer,  contains  no  platinum  metals.  The  next  con- 
tains some  particles  of  the  zinc  and  platinum  alloy,  im- 
bedded in  the  basic  zinc  chloride  ;  it  is  porous,  and  not 
very  thick.  The  inner  stratum  consists  of  a  beautiful 
crystalline  regulus. 

To  obtain  the  alloy  from  the  middle  stratum,  it  is  only 
necessary  to  wash  repeatedly  with  water ;  and  the  alloy 
gained  is,  of  course,  to  be  added  to  the  regulus.  To 
obtain  this  regulus  as  pure  as  possible,  it  is  again  fused 
with  500  grms.  of  zinc  and  some  ammonium  chloride,  then 
granulated  in  water,  and  the  granules  dissolved  in  fuming 
hydrochloric  acid.  The  acid  attacks  the  regulus  with  the 
greatest  energy,  and  the  solution  is  complete  in  less  than 
an  hour.  The  zinc  chloride  can  be  used  for  the  next 
operation. 

The  platinum  metals  are  found  at  the  bottom  of  the 
vessel,  in  the  form  of  a  finely-divided  black  powder,  which 

-     z  z 


706  THE   ASSAY   OF    PLATINUM. 

is  contaminated  with  zinc,  and  with  traces  of  iron,  copper, 
&c.,  from  the  latter.  It  cannot  be  purified  with  nitric 
acid,  nor  with  aqua  regia,  for  part  of  the  platinum  metals 
will  thereby  be  dissolved,  or,  at  best,  so  suspended  in  the 
fluid  that  filtration  is  impossible.  If,  however,  the  powder 
is  treated  with  hydrocholoric  acid,  singularly  enough,  all 
the  impurities  are  dissolved  ;  not  only  zinc  and  iron,  but 
also  lead  and  copper,  dissolve  readily  with  the  generation 
of  hydrogen.  The  explanation  is  readily  found  in  elec- 
trical currents  produced  by  the  contact  of  the  metals,  the 
stream  passing  from  the  positive  zinc,  iron,  &c.,  to  the 
negative  platinum  metals,  hydrogen  being  given  from  the 
latter,  and  chlorine  from  the  former,  and  uniting  with 
them.  The  metallic  powder,  after  thorough  washing, 
possesses  the  property,  upon  being  gently  heated,  of  ex- 
ploding weakly,  and,  when  highly  heated,  with  violence, 
the  explosion  being  accompanied  with  the  evolution  of 
light,  although  neither  hydrogen,  chlorine,  nitrogen,  nor 
aqueous  vapour  are  given  off;  and,  as  these  are  the  only 
elements  which  it  is  possible  that  the  metallic  powder 
could  have  taken  up,  it  must  be  assumed  that  these  metals 
are,  by  this  treatment,  converted  into  an  allotropic  con- 
dition, and  that,  upon  heating,  they  return,  with  more 
or  less  energy,  to  their  original  condition.  The  powder 
contains,  mainly,  rhodium  and  iridium ;  but  there  are 
traces  present  of  platinum,  palladium,  lead,  copper,  iron, 
and  zinc 

It  is  intimately  mixed  with  about  3  or  4  times  its 
weight  of  completely  anhydrous  barium  chloride,  and  a 
stream  of  chlorine  gas  led  over  it  at  a  tolerably  high 
temperature.  The  operation  is  concluded  when  particles 
of  ferric  chloride  show  themselves  on  the  neck  of  the  flasks 
containing  the  powder.  These  are  carefully  brushed  away 
with  filter-paper.  Some  water  is  now  added,  and  the 
mass  of  the  platinum  metals  dissolved  with  the  evolution 
of  heat.  There  remains  behind  insoluble  matter,  which, 
upon  reduction  with  hydrogen,  alloying  with  zinc,  and 
treatment  with  hydrochloric  acid,  furnishes  ruthenium. 
From  the  solution  all  the  barium  chloride  is  removed  by 


ASSAY    OF   PLATIXUM    ORES.  707 

careful  addition  of  sulphuric  acid.  The  platinum  metals 
are  now  completely  freed  from  all  other  metals  by  reduc- 
tion with  hydrogen,  the  temperature  being,  throughout 
the  operation,  maintained  at  nearly  100°  C.,  by  means  of 
a  constant  water-bath.  Platinum  and  palladium  chiefly 
separate  first ;  then  mainly  rhodium ;  and  the  last  por- 
tions consist  almost  entirely  of  iridium.  It  is  best  to 
break  off  the  operation  when  the  fluid  has  assumed  a 
greenish-yellow  colour.  The  last  portions  of  iridium 
(obtained  by  evaporating  the  solution  to  dryness,  fusing 
with  sodium  carbonate,  and  treatment  with  aqua  regia) 
are  added  to  the  portion,  afterwards  to  be  again  rendered 
workable  by  renewed  treatment  with  barium  chloride. 
The  operation  of  reduction  is  hastened  by  concentrating 
the  fluid  ;  in  doing  which  care  must  be  taken  to  guard 
against  explosion,  on  account  of  the  hydrogen.  The 
separated  metals  are  treated  with  aqua  regia,  and  the 
platinum  and  palladium  thus  dissolved  separated  from 
each  other  as  already  described.  The  traces  ,of  rhodium 
and  iridium  in  the  mother  liquid  can  be  removed  entirely 
by  continued  boiling  with  potassium  iodide  (whereby  they 
precipitate  as  iodides)  ;  they  are  then  dissolved  in  aqua 
regia  and  added  to  the  insoluble  portion. 

This  insoluble  and  partly-oxidised  portion  is  now  again 
reduced  by  hydrogen  gas,  treated,  as  before  described,  with 
barium  chloride,  and,  after  the  removal  of  the  barium,  the 
last  traces  of  platinum  and  palladium  removed  by  boiling 
with  caustic  soda.  Ehodium  and  iridium  now  alone  remain 
to  be  separated. 

The  brown-red  fluid  is,  for  this  purpose,  evaporated 
with  hydrochloric  acid,  and,  after  filtration,  treated  with 
sodium  bisulphite  in  great  excess,  and  the  whole  allowed 
to  remain  quietly  in  the  cold  for  several  days.  The  double 
rhodium  and  sodium  sulphide  separates  slowly,  giving  a 
lemon-yellow  precipitate.  The  solution  becomes  lighter 
and  lighter,  and  finally  almost  colourless.  The  colour  of 
the  precipitate  changes  with  that  of  the  fluid,  becoming, 
with  it,  lighter.  This  precipitate,  upon  washing,  contains 
the  rhodium  almost  pure. 


z  z  2 


708  THE   ASSAY   OF    PLATINUM. 

Upon  heating  the  fluid  gently,  a  yellow-white  pre- 
cipitate separates,  which  consists  mainly  of  rhodium,  but 
contains  also  some  iridium.  After  filtering  olF  this  pre- 
cipitate, the  solution,  upon  being  concentrated  to  a  small 
volume,  gives  yet  two  precipitates — 

1.  A  curdy,    slowly-separating,    yellowish-white    pre- 
cipitate containing  nearly  chemically  pure  iridium,  with 
but  the  faintest  traces  of  rhodium. 

2.  A  heavy,    crystalline  powder,   quickly  separating,, 
which  is  readily  freed  from  the  first  by  decant ation.    Upon 
testing,  it  gives  all  the  reactions  for  iridium,  but  likewise 
some  peculiar  reactions  not  shown  by  the  latter. 

The  complete  separation  of.  rhodium  from  iridium  is 
accomplished  by  treating  the  yellow  precipitates  with 
concentrated  sulphuric  acid.  They  are  added  in  small 
portions  to  the  acid,  heated  in  a  porcelain  capsule  until 
all  the  sulphurous  acid  has  escaped,  and  then  left  upon  the 
sand-bath  until  the  free  sulphuric  acid  has  been  driven  off 
and  sodium  sulphate  formed.  Upon  boiling  the  mass  in 
water,  all  the  iridium  dissolves  as  sulphate,  with  a  chrome- 
green  colour,  while  the  rhodium  remains  behind  as  a  flesh- 
coloured  double  salt  of  sodium  and  rhodium.  The  latter 
is  boiled  in  aqua  regia,  and  washed  by  decantation.  It 
is  insoluble  in  water,  hydrochloric  or  nitric  acids,  and  in 
aqua  regia.  The  rhodium  and  iridium  are  now  completely 
separated. 

The  first  yellow  precipitate  obtained  in  the  cold  by  the 
sodium  bisulphite  gives,  by  this  treatment,  the  rhodium 
quite  pure.  The  second  and  third  precipitates,  containing 
much  iridium,  give  a  very  fine  rhodium,  but  still  slightly 
contaminated  with  iridium.  The  products,  therefore, 
obtained  by  this  treatment  with  sulphuric  acid  (which 
betray  their  contamination  with  iridium  by  their  somewhat 
brownish  colour)  are  collected  for  themselves,  the  rhodium 
separated  therefrom  by  glowing,  treated  again  with  barium 
chloride,  and  the  operation  of  separation  repeated.  The 
green  solution,  containing  only  iridium,  is  gradually  heated 
over,  an  ordinary  burner,  in  a  porcelain  capsule,  and  after- 
wards upon  the  sand-bath,  to  remove  the  excess  of  sul- 


C.    LEA  S   PROCESS.  709 

phuric  acid ;  and,  finally,  the  capsule  and  its  contents  are 
highly  heated  in  a  Hessian  crucible.  There  is  formed 
thereby  sodium  sulphate  and  iridium  sesquioxide.  Upon 
boiling  the  mass  with  water,  the  last  remains  behind  as 
a  black,  insoluble  powder,  which  is  readily  washed  by 
decantation. 

C.  Leas  Process  for  Analysing  Platinum  Ores. — The 
ores  on  which  these  analyses  were  performed  contained 
chiefly  iridium,  together  with  ruthenium,  osmium,  rhodium, 
and  platinum.  It  was  a  Californian  osmiridium  which  had 
already  undergone  a  preliminary  fusion  with  nitre  and 
caustic  potash. 

This  material  is  boiled  with  aqua  regia  to  extract  all 
the  soluble  portions,  the  residue  then  ignited  with  nitre 
and  caustic  soda,*  and  the  fused  mass  heated  with  water. 
From  the  resulting  solution  small  portions  of  potassium 
osmite  crystallise  out.  The  metallic  oxides  are  next  pre- 
cipitated, and  this  precipitate,  together  with  the  portions 
insoluble  in  water,  is  boiled  again  with  aqua  regia,  ignited 
again,  &c.  These  ignitions  still  leave  a  small  portion  of 
unattacked  residue. 

The  boiling  with  aqua  regia  is  continued  for  a  long 
time,  in  order  to  get  rid  as  thoroughly  as  possible  of  the 
osmic  acid.  Even  200  hours  boiling,  however,  still  leave 
osmium  in  the  solution  in  easily  recognisable,  but  in  com 
paratively  small,  quantity.  The  greatest  advantage  is 
found  throughout  the  whole  of  this  part  of  the  operation 
from  the  use  of  a  blowing  apparatus,  by  the  aid  of  which 
all  inconvenience  from  the  fumes  of  osmic  acid  is  avoided. 
The  apparatus  is  constantly  swept  clear  by  a  powerful  air 
current,  and  the  osmic  acid  is  removed  as  fast  as  it  is 
volatilised.  As  the  ignition  of  the  ore  with  alkaline  nitrate 
and  caustic  alkali  scarcely  drives  off  any  osmium,  and 
^s  almost  all  inconvenience  in  manipulating  the  resulting 

*  Attention  is  necessary  to  the  order  in  which  these  substances  are  employed. 
If  the  caustic  soda  is  melted  first,  it  attacks  the  iron  vessel  strongly,  and  may 
even  go  through.  If  added  last  it  causes  sudden  and  violent  effervescence,  with 
danger  of  boiling  over.  Therefore,  place  the  nitre  first  in  the  vessel,  and  when 
it  is  fused  add  the  caustic  soda.  When  a  red  heat  is  obtained  add  the  osmiridium 
by  degrees. 


710  THE   ASSAY    OF    PLATINUM. 

solutions  can  be  avoided  by  throwing  down  the  metals  with 
alcohol  from  the  hot  alkaline  solution,  in  place  of  using 
acid,  it  is  clear  that  the  difficulties  arising  from  the  noxious 
effects  of  osmic  acid  can  be  almost  wholly  removed  from 
each  of  the  various  stages  of  the  process. 

A  very  prolonged  treatment  with  aqua  regia  is  found  to 
have  the  great  advantage  of  converting  nearly  the  whole 
of  the  ruthenium  into  bichloride.  The  separation  of 
ruthenium  in  this  form  from  the  other  metals  is  so  easy  in 
comparison  with  the  difficulties  presented  by  the  separation 
of  the  sesquichloride,  that  this  advantage  cannot  be  looked 
upon  as  other  than  a  very  material  one. 

Sal-ammoniac  is  next  added  to  the  mixed  solution  in 
quantity  sufficient  to  saturate  it.  The  sandy  crystalline  pre- 
cipitate (A)  is  thoroughly  washed  out,  first  with  saturated^ 
and  then  with  dilute  sal-ammoniac  solution.  The  saturated 
solution  of  ammonium  salt  carries  through  with  it  nearly 
the  whole  of  the  ruthenium  as  bichloride  (B)  ;  the  dilute 
solution  is  found  to  contain  small  quantities  of  iridium, 
rhodium,  and  ruthenium  (C). 

Over  (A),  water  acidulated  with  hydrochloric  acid  is- 
placed,  and  allowed  to  stand  for  some  days.  This  is  treated 
with  ammonia  and  boiled.  The  precipitate,  when  treated 
with  hydrochloric  acid,  furnishes  green  osmium  chloride,, 
with  traces  of  ruthenium. 

In  these  preliminary  steps,  Claus's  process  has  been 
followed,  which  undoubtedly  offers  advantages  over  any 
other,  and  best  brings  the  metals  into  a  convenient  state 
for  separation,  varying  it  only  by  prolonging  the  treatment 
with  aqua  regia,  and  converting  the  ruthenium  principally 
into  bichloride  instead  of  sesquichloride. 

We  have  now  three  portions  of  material : — (A),  con- 
sisting of  ammonium  iridiochloride,  containing  also  ruthe- 
nium, osmium,  rhodium  and  platinum  in  small  quantities. 
(The  ore  under  examination  contained  no  palladium,  which 
metal,  if  present,  has  always  its  own  peculiar  mode  of 
separation,  and  does  not  enhance  the  difficulties  of  opera- 
tion.) (B),  containing  ruthenium  bichloride,  together 
with  iron  in  quantity,  copper,  and  other  base  metals  which 


c.  LEA'S  PROCESS.  711 

may  be  present.  Finally  (C),  containing  chiefly  ruthenium 
bichloride,  mixed  with  small  quantities  of  iridium  and 
rhodium. 

The  next  step  in  the  process  is  to  introduce  the  am: 
monium  iridiochloride  (A)  into  a  large  flask  with  twenty 
to  twenty-five  times  its  weight  of  water,  and  apply  heat 
until  the  solution  is  brought  to  the  boiling-point ;  the 
whole  of  the  ammonium  iridiochloride  should  be  brought 
into  solution  in  order  that  the  reduction  to  be  effected 
may  not  occupy  too  long  a  time,  as  otherwise  the  platinum 
and  ruthenium  salt,  if  any  be  present,  might  likewise  be 
attacked.  Crystals  of  oxalic  acid  are  thrown  in  as  soon  as 
the  solution  actually  boils,  whereupon  a  lively  efferves- 
cence takes  place,  and  the  iridium  salt  is  rapidly  reduced. 
As  fast  as  the  effervescence  subsides,  more  oxalic  acid  is 
added  until  further  additions  cease  to  produce  any  effect. 
When  this  is  the  case,  the  liquid  is  allowed  to  boil  for  two 
or  three  minutes  longer,  not  more  ;  the  heat  is  to  be  re- 
moved, and  the  flask  plunged  into  cold  water. 

By  this  treatment  any  platinum  present  is  unaffected. 
Sal-ammoniac  in  crystals  is  added,  about  half  enough  to 
saturate  the  quantity  of  water  present.  The  sal-ammoniac 
may  be  added  immediately  before  the  flask  is  removed 
from  the  fire.  After  cooling,  the  solution  should  be  left  for 
a  few  days  in  a  shallow  basin,  whereby  the  ammonium 
platinochloride  will  separate  out  as  a  yellow,  a  reddish,  or 
even  (especially  if  the  quantity  of  water  used  was  insuffi- 
cient) as  a  black  crystalline  powder,  according  to  the 
quantity  of  iridium  which  it  may  contain. 

The  mother  liquor  is  to  be  again  placed  in  a  flask,  and 
boiled  with  aqua  regia.  On  cooling,  the  ammonium  iridio- 
chloride crystallises  out,  and  any  traces  of  rhodium  and 
ruthenium  which  may  be  present  remain  in  solution.  The 
iridium  salt  is  to  be  washed  with  a  mixture  of  two  parts 
of  a  saturated  solution  of  sal-ammoniac  and  three  parts  of 
water,  and  may  then  be  regarded  as  pure. 

The  treatment  by  oxalic  acid  affords  iridium  free  from 
all  traces  of  ruthenium. 

The  treatment  of  solutions  (B)  and   (C)  presents  no 


712  THE   ASSAY   OF   PLATINUM. 

difficulty.  With  (B)  the  best  plan  is  to  place  the  solution 
aside  in  a  beaker  covered  with  filter  paper  for  some  time. 
Treated  in  this  way,  the  bichloride  gradually  crystallises 
put,  and  by  re-crystallisations  may  be  obtained  in  a  state 
of  perfect  purity. 

Solution  (C)  is  to  be  evaporated  to  dryness,  and  re- 
duced to  an  impalpable  powder.  It  is  then  to  be  thrown 
upon  'a  filter,  and  thoroughly  washed  with  a  perfectly 
saturated  solution  of  sal-ammoniac.  The  ruthenium  bi 
chloride  is  thus  carried  through,  with  perhaps  a  trace  of 
rhodium  sesquichloride,  from  which,  however,  it  is  easily 
freed  by  crystallisation.  From  the  residue,  the  rhodium 
and  ammonium  sesquichloride  is  removed  by  a  dilute  solu- 
tion of  sal-ammoniac,  perfectly  free  from  the  iridium,  which 
is  left  behind. 

In  connection  with  this  separation,  Mr.  Lea  makes  a 
remark  which,  though  of  special  reference  to  this  par- 
ticular case,  is  also  applicable  to  all  those  cases  in  which 
the  double  chlorides  of  the  platinum  metals  are  to  be 
separated  by  their  various  solubilities  in  solution  of  sal- 
ammoniac.  This  most  valuable  process,  for  which  we  are 
indebted,  as  for  so  much  else,  to  Glaus,  whose  untiring 
labours  have  made  him  the  father  of  this  department  of 
chemistry,  requires  to  be  applied  with  some  attention  to 
minutige. 

The  crystalline  matter  must  be  reduced  to  the  finest 
powder,  and  after  being  thrown  upon  the  filter  it  must  be 
washed  continuously  until  the  separation  is  effected.  Any 
interruption  of  the  washing  is  followed  by  more  or  less 
crystallisation  of  sal-ammoniac  through  the  material,  which 
precludes  an  effectual  separation.  The  same  material  which 
in  a  state  of  coarse  powder  will  hardly  yield  up  enough 
ruthenium  bichloride  to  colour  the  sal-ammoniac  solution, 
will,  when  thoroughly  pulverised,  give  an  almost  opaque 
blood-red  filtrate. 

Solution  (C)  may  be  subjected  to  a  different  treatment 
from  the  foregoing,  and  oxalic  acid  may  be  used  to  effect 
the  separation.  The  solution  is  to  be  brought  to  the  boil- 
ing-point, and  oxalic  acid  added  as  long  as  effervescence 


c.  LEA'S  PROCESS.  713 

is  produced.  The  iridium  bichloride  is  thereby  reduced, 
the  ruthenium  bichloride  and  the  rhodium  sesquichloride 
are  not  affected.  Sal-ammoniac  is  then  to  be  dissolved 
in  the  solution  to  thorough  saturation.  By  standing  and 
repose  the  double  rhodium  and  ammonium  chloride  sepa- 
rate out.  The  solution  is  then  re- oxidised  by  boiling  with 
aqua  regia  ;  by  standing  for  some  days  in  a  cool  place,  the 
ammonium  iridiochloride  crystallises  out,  and  the  super- 
natant solution  contains  the  double  ammonium  chloride 
and  ruthenium  bichloride,  which  may  be  rendered  pure 
by  several  re-crystallisations. 

For  purifying  the  double  iridium  and  ammonium 
chloride  the  oxalic  process  is  decidedly  the  best.  It  is 
simple  and  less  trouble,  and  there  is  the  further  advantage 
that  the  platinum  is  left  in  the  condition  of  double  chloride, 
whereas  when  the  usual  method  of  treating  with  aqueous 
sulphuretted  hydrogen  is  used,  the  platinum  is  apt  to  be 
converted  partly  into  sulphide,  together  with  any  traces  of 
rhodium  and  ruthenium  which  may  be  present.  When 
oxalic  acid  is  used,  the  platinum  remains  behind  as  a  red- 
dish powder,  containing  some  iridium,  from  which  it  may 
be  freed  in  the  ordinary  manner,  if  it  is  present  in  quantity 
sufficient  to  be  worth  working. 

For  treating  a  mixture  such  as  that  which  is  here  de- 
signated as  (C),  containing  no  platinum,  and  only  ruthenium 
present  in  the  form  of  ammonium  rutheniochloride,  it  is 
unnecessary  to  apply  reducing  agents,  and  the  first 
method  described  is  the  best.  But  if  it  be  proposed  to 
effect  the  separation  by  the  reduction  of  the  iridium  com- 
pound, the  method  here  described  is  preferable  to  that 
based  on  the  use  of  sulphuretted  hydrogen  even  in  this 
case. 

The  action  of  oxalic  acid  on  the  platinum  metals  is 
interesting  ;  its  reducing  effect  upon  iridium  bichloride  at 
the  boiling-point  is  immediate.  On  ruthenium  bichloride 
it  seems  to  have  no  effect  whatever,  and  they  may  be  boiled 
together  for  a  length  of  time  without  sensible  result.  In  a 
trial  made  with  ruthenium  and  ammonium  eesquichloride, 
the  oxalic  acid  was  boiled  with  the  metallic  salt  for  a  con- 


714  THE   ASSAY   OF   PLATINUM. 

siderable  time  without  any  effect  becoming  visible,  but 
by  long-continued  boiling  a  gradual  precipitation  took 
place.  When  ammonium  platinochloride.  was  boiled  with 
oxalic  acid,  no  effect  was  produced  for  a  considerable 
time,  but  gradually  the  platinum  salt  diminished  in  quan- 
tity, and  the  liquid  acquired  a  stronger  yellow  colour, 
perhaps  owing  to  formation  of  soluble  platinic  oxalate. 
This  process  will  not,  however,  furnish  an  easy  and  conve- 
nient method  of  purifying  commercial  platinum  from  the 
iridium  always  found  in  it,  as  the  reduction  of  very  small 
quantities  of  double  iridium  and  ammonium  chloride  in 
the  presence  of  a  large  proportion  of  the  corresponding 
platinum  salt  is  difficult  and  slow,  and  the  platinum  salt 
itself  is  evidently  attacked. 

The  following  method  of  Analysis  of  Platinum  Ores,  by 
MM.  DEVILLE  and  H.  DEBRAY,  may  be  useful.  The  ores  of 
platinum  contain  the  following  substances  : — 

1.  Sand.      The  whole  of  the  sand  is  never  removed 
by  washing  the  ore ;    and    the    sand    contains    quartz, 
zircon,  chromate  of  iron,  and,  in  the  Eussian  ores,  titanate 
of  iron. 

2.  Osmiridium. 

3.  Platinum,  iridium,  rhodium,  and  palladium,  combined, 
no  doubt  in  the  form  of  an  alloy. 

4.  Copper  arid    iron,  which   exist  in   the    ores    in  a 
metallic  state,  for  the  iron  found  in  the  sand  is  not  soluble 
in  acids. 

5.  Gold,  and,  oftener  than  is  supposed,  a  little  silver. 
The  latter  metal  is  generally  found  with  the  palladium, 
and  it  is  very  rarely  that  palladium  is  obtained  quite  free 
from  silver  when  it  is  prepared  by  the  old  processes. 

1.  Sand. — To  estimate  the  sand  we  take  a  small  assay 
crucible,  or  an  ordinary  crucible  with  smooth  sides,  and 
melt  in  it  a  little  borax,  so  as  to  glaze  the  inside.  We  now 
introduce  from  7  to  10  grammes  of  pure  granulated  silver,- 
and  2  grammes  of  the  ore  fairly  taken  and  weighed  very 
accurately.  Over  the  platinum  we  put  10  grammes  of 
fused  borax,  and  one  or  two  small  pieces  of  wood  charcoal. 
The  silver  is  now  melted,  and  care  must  be  taken  to  keep 


DEVILLE   AND    DEBRAY'S   PROCESS.  715 

it  for  some  time  a  little  hotter  than  the  melting  point,  so 
that  the  borax  may  be  very  liquid,  and  may  dissolve  the 
vitreous  matters  which  accompany  the  platinum  and  con- 
stitute the  sand.  The  crucible  is  now  allowed  to  cool,  and 
when  it  is  cold,  the  button,  which  will  contain  the  silver, 
osmium,  platinum,  and  all  the  other  metals,  is  detached, 
and  if  necessary  digested  for  a  time  with  weak  fluoric  acid 
to  remove  the  last  portions  of  borax.  It  is  now  heated  to 
a  faint  redness,  and  then  weighed.  The  weight  of  the 
button,  subtracted  from  the  sum  of  the  weight  of  the  ore 
and  silver  employed,  will  give  the  amount  of  sand  con- 
tained in  the  ore.  For  example  :— 

Milligr. 

Californian  ore 2000 

Silver 7221 

9221 
After  fusion,  the  button  weighed      .         .     9162 

Consequently,  the  ore  contained,  sand       .         59 

It  is  very  important  to  know  this  number,  for  it  represents 
the  only  matter  absolutely  destitute  of  value  which  the 
ore  contains  ;  and  this  simple  operation  may  be  considered 
the  most  important  performed  in  estimating  the  value  of 
an  ore.  It  is,  besides,  performed  so  quickly,  that  it  is  as 
well  to  do  at  the  same  time  two  or  three  specimens,  taken 
from  different  parts  of  a  lot  of  platinum  powder. 

2.  Osmiridium. — Another  2  grammes  of  the  ore  weighed 
very  accurately  are  treated  with  aqua  regia  at  70°  (Cent.) 
until  the  platinum  is  entirely  dissolved.  The  aqua  regia 
must  be  renewed  occasionally  for  12  or  15  hours,  or  until 
it  is  no  longer  coloured.  It  is  best  to  perform  this  opera- 
tion in  a  large  beaker,  and  to  place  a  cover  over  it  to  pre- 
vent loss.  The  solution  must  be  decanted  with  the  greatest 
care  from  the  metallic  spangles  of  the  osmiridium  and  the 
sand  which  remain  at  the  bottom  of  the  beaker.  If  neces- 
sary it  may  be  filtered,  but  as  little  as  possible  of  the 
osmide  must  be  allowed  to  go  on  the  paper.  The  insoluble 
residue  must  be  washed  by  decantation,  then  dried  and 
weighed,  after  having  added  what  remained  on  the  filter. 
By  subtracting  the  weight  of  the  residue  from  the  weight 


716  THE    ASSAY    OF    PLATINUM. 

of  the  sand  obtained  in  the  former  operation,  we  obtain  the 
weight  of  the  osmiridium.  For  instance,  in  the  Californian 
ore  we  had  : — 

Milligr. 

Osmiridium  and  sand  .         .       V      V        .     81 
Sand    .  •      .        »        »       '.      ~.       ••  /      •     59 

Osmiridium  •        .         .    „ ''  ,         .         .         .22 

The  button  obtained  in  determining  the  sand  might  be 
employed  in  this  operation.  In  that  case  it  is  necessary  to 
dissolve  out  the  silver  with  nitric  acid,  and  then  proceed 
with  the  residue,  as  we  have  just  directed. 

3.  Platinum  and  Iridium. — The  solution  in  aqua  regia 
obtained  in  the  last  operation  is  evaporated  to  dryness  at  a 
low  temperature,  and  the  residue  is  re-dissolved  in  a  small 
quantity  of  water  (if  it  should  not  entirely  dissolve  in  the 
water,  some  more  aqua  regia  must  be  added,  and  the  evapo- 
ration repeated),  to  which  is  added  about  twice  as  much 
pure  alcohol ;  lastly,  we  add  a  great  excess  of  sal  ammoniac 
in  crystals.  The  whole  is  now  slightly  warmed  to  com- 
plete the  solution  of  the  sal  ammoniac ;  it  is  then  stirred, 
and  afterwards  set  aside  for  24  hours.  The  orange-yellow, 
or  even  reddish-brown,  precipitate  which  is  formed  con- 
tains the  platinum  and  the  iridium,  but  some  remains  in 
the  solution.  The  precipitate  must  be  thrown  on  a  filter 
and  washed  with  alcohol.  Afterwards  the  filter  is  dried 
in  a  platinum  crucible,  placed,  for  greater  safety,  within  a 
larger  one,  and  afterwards  heated  by  degrees  to  low  redness- 
The  crucibles  are  now  uncovered,  and  the  filter  is  burnt  at 
the  lowest  possible  temperature.  Once  or  twice  after  the 
incineration  of  the  filter  a  piece  of  paper  saturated  with 
turpentine  should  be  introduced  into  the  crucible,  by 
which  means  the  iridium  oxide  will  be  reduced,  and  the 
expulsion  of  the  last  traces  of  osmium  will  be  effected. 
The  crucible  is  now  heated  to  whiteness  until  it  no  longer 
loses  weight,  or  the  reduction  is  finished  in  a  current  of 
hydrogen. 

The  liquid  separated  from  the  platinum-yellow  by  fil- 
tration is  evaporated  until  the  ammonium  chloride  crys- 
tallises in  great  quantity.  It  is  allowed  to  cool,  is  then 


DEVILLE   AND   DEBRAY'S   PROCESS.  717 

decanted,  arid  on  a  filter  is  collected  a  small  quantity  of 
a  deep  violet-coloured  salt,  which  is  the  iridium  ammonio- 
chloride  mixed  with  a  little  of  the  platinum  salt.  This  is 
first  washed  with  a  solution  of  sal  ammoniac,  and  then  with 
alcohol.  The  salt  is  then  ignited,  and  if  necessary  reduced 
by  hydrogen  like  the  platinum  salt.  The  mixture  of  pla- 
tinum and  iridium  obtained  by  the  two  reductions  is  then 
weighed.  The  two  metals  are  now  digested  at  about  40° 

o  o 

or  50°  (Cent.)  in  aqua  regia,  diluted  with  about  4  or  5 
times  its  weight  of  water — the  aqua  regia  being  renewed 
until  it  is  no  longer  coloured.  The  residue  is  pure  iridium. 
To  obtain  the  weight  of  the  platinum  the  weight  of  the 
iridium  is  subtracted  from  that  of  the  mixture  of  the  two. 
This  method  of  separating  the  two  metals  is  very  accurate 
if  the  aqua  regia  used  be  weak,  and  the  contact  with  it 
prolonged. 

4.  Palladium,  Iron,  and  Copper. — The  liquid  charged 
with  sal  ammoniac  and  alcohol,  from  which  the  platinum 
and  iridium  have  been  separated,  is  evaporated  to  get  rid 
of  the  alcohol,  and  then  treated  with  an  excess  of  nitric 
acid,  which  transforms  the  ammonium  chloride  into  nitro- 
gen and  hydrochloric  acid.  It  is  now  evaporated  almost 
to  dryness.  The  residue  is  removed  to  a  covered  porcelain 
crucible  which  is  weighed  with  great  care.  When  the 
matter  is  dry  it  is  moistened  with  concentrated  ammonium 
sulphide  and  afterwards  dusted  over  with  2  or  3  grammes 
of  pure  sulphur.  When  dry  this  crucible  is  placed  within 
a  larger  one  of  clay,  and  surrounded  with  pieces  of  wood 
charcoal.  The  two,  covered,  are  now  set  in  a  cold  furnace 
which  is  filled  up  with  charcoal,  and  the  fire  is  lighted 
at  the  top  to  avoid  the  projection  of  any  matter  from  the 
crucible,  if  it  were  too  quickly  heated.  After  reaching  a 
bright  red  heat,  the  crucibles  are  allowed  to  cool.  The 
porcelain  crucible  now  contains  palladium  in  a  metallic 
state,  with  the  sulphides  of  iron  and  copper,  and  also  the 
o-old  and  rhodium.  This  mixture  is  moistened  with  con- 
centrated nitric  acid,  which,  after  prolonged  digestion  at 
70°,  dissolves  the  palladium,  iron,  and  copper,  forming  at 
the  same  time  a  little  sulphuric  acid.  The  solution  of  the 


718  THE   ASSAY   OP   PLATINUM. 

nitrates  is  poured  off  from  the  residue,  which  is  washed  by 
decantation,  and  the  solutions  and  washings  are  evaporated 
to  dry  ness,  and  then  calcined  at  a  strong  red  heat.  In  this 
way  the  palladium  is  reduced,  and  the  iron  and  copper 
pass  to  the  state  of  oxides,  which  are  easily  separated  from 
the  palladium  by  means  of  strong  hydrochloric  acid.  The 
palladium  remains  in  the  crucible,  in  which  it  is  again 
strongly  ignited  and  then  weighed. 

The  iron  and  copper  chlorides  are  now  evaporated  to 
dryness  at  a  temperature  but  little  above  100°  (Cent.)  and 
are  then  treated  with  ammonia.  The  ferric  chloride  having 
lost  nearly  all  its  acid,  has  become  insoluble  ;  but  the  copper 
chloride  is  readily  dissolved,  and  may  be  filtered  from  the 
iron  which  is  washed,  ignited,  and  weighed.  The  copper 
solution  is  now  evaporated  almost  to  dryness,  and  then  mixed 
with  excess  of  nitric  acid,  and  heated  to  drive  off  the  am- 
monium chloride.  Afterwards  the  copper  nitrate  is  ignited 
and  weighed.  The  weight  of  the  copper  is  always  so  small 
that  the  hygroscopic  water  the  copper  oxide  may  absorb 
may  be  neglected. 

5.  Gold  and  Platinum. — The  residue  insoluble  in  nitric 
acid  is  weighed  and  treated  with  very  dilute  aqua  regia 
which  takes  up  the  gold,  and  sometimes,  but  very  rarely, 
traces  of  platinum.     To  ascertain  if  platinum  be  present, 
evaporate  to  dryness,  and  re-dissolve  by  alcohol  and  am- 
monium chloride.     If  any  platinum-yellow  remain,  it  must 
be  ignited  and  weighed.     The  difference  in  the  weight  of 
the  porcelain  crucible  before  and  after  the  treatment  by 
aqua  regia,  gives  the  weight  of  the  gold,  from  which,  if 
any  be  found,  the  weight  of  the  platinum  must  be  deducted. 

6.  Rhodium. — The  residue  left  in  the  crucible  is  rho- 
dium, which  must  be  reduced  in  a  current  of  hydrogen. 

We  append  the  results  of  some  analyses  of  platinum 
ores,  by  MM.  Deville  and  Debray.  (See  Table  on  next  page.) 

M.  A.  Guyard  gives  the  following  process  for  the  ex- 
traction of  metals  from  platiniferous  residues  : — 

'  This  process  comprises  three  different  operations,  which 
I  will  succinctly  describe. 

'  1.  Solution  of  the  Residues.  — The  mother  liquors  which 


GUYARDS    PROCESS. 


719 


ANALYSES  OF  PLATINUM:  ORES  FROM  VARIOUS  SOURCES. 


Columbia 

California 

Oregon 

Spain 

Australia 

Russia 

Platinum 

80-00 

79-85 

51-45 

45-70 

59-80 

77-50 

Iridiuiii 

1-55 

4-20 

0-40 

0-95 

2-20 

1-45 

Hhodium 

2-50 

0-65 

065 

2-65 

1-50 

2-80 

Palladium 

1-00 

1-95 

0-15 

0-85 

1-50 

0-85 

Gold   . 

1-50 

0-55 

0-85 

3-15 

2-40 

(*) 

Copper 

0-65 

0-75 

2-15 

1-05 

1-10 

2-15 

Iron    . 

7-20 

4-95 

4-30 

6-80 

4-30 

960 

Osmiridium 

1-40 

4-95 

37-30 

2-85 

25-00 

2-35 

Sand  . 

4-35 

260 

300 

35-95 

1-20 

1-00 

Osmium  and  loss 

— 

0-05 

— 

0-05 

0-80 

2-30 

100-15 

100-00 

100-25 

100-00 

100-00 

100-00 

remain  after  the  precipitation  of  platinum  by  sal  ammoniac 
come  from  solutions  of  crude  or  commercial  platinum. 
They  always  contain  iron,  mostly  produced  from  the  iron 
sulphate  used  for  the  precipitation  of  gold,  lead,  copper, 
palladium,  platinum,  and  especially  rhodium.  These  mother 
liquors  are  acidulated  by  hydrochloric  acid,  and  are  then 
ready  to  be  investigated.  To  recall  their  composition,  I 
shall  distinguish  them  here  only  as  residues  in  solution.  It 
need  only  be  mentioned  that  iron,  which  is  generally  used 
for  the  precipitation,  must  be  avoided. 

'  Solid  residues  are  melted  at  once  with  three  times 
their  weight  of  a  mixture  of  equal  parts  of  soda  and  sodium 
nitrate.  The  fusion  is  effected  at  a  bright  red  heat  in  a 
thick  iron  vessel.  It  is  accomplished  without  bubbling  or 
projection,  and  requires  about  an  hour.  During  the  last, 
twenty  minutes  the  mass  must  be  constantly  stirred  with 
an  iron  spoon.  The  operation  is  extremely  simple. 

'  These  residues  contain  osmiridium,  unattackable  by  all 
chemical  agents,  attackable  osmide,  some  grains  of  triple 
alloy  of  platinum,  iridium,  and  rhodium,  which  aqua  regia 
will  not  dissolve,  but  which  nitre  completely  oxidises  and 
completely  breaks  up.  They  also  contain  the  gangue 
characteristic  of  platinum  ores — quartz,  silicates  of  all 
bases,  titanates,  hyacinths,  &c.,  &c. 

'  The  mixture  I  make  use  of  oxidises  all  that  is  oxidis- 


*  Gold,  if  any,  counted  in  the  loss. 


720  THE   ASSAY   OF   PLATINUM. 

able,  and  breaks  up  the  gangue,  which  it  partly  dissolves. 
The  melted  mass  contains  all  the  bodies  above  mentioned, 
besides  a  large  quantity  of  iron  oxide  taken  from  the  sides 
of  the  vessel  in  which  the  operation  is  performed.  The 
fused  mass  is  poured  into  cast-iron  moulds.  When  solid 
it  is  broken  into  fragments  and  boiled  with  sufficient  water 
to  obtain  a  strong  solution  of  soda,  capable  of  holding  all 
the  gelatinous  acids  in  solution.  It  also  contains  osmium 
in  the  state  of  osmiate.*  It  is  filtered  from  insoluble 
matter,  and  then  supersaturated  with  hydrochloric  acid. 
The  insoluble  oxides  are  freed  by  washing  from  the  excess 
of  alkali,  and  are  then  dissolved  in  aqua  regia. 

'  This  solution  contains  iron,  copper,  lead,  iridium, 
rhodium,  platinum,  and  ruthenium.  It  is  separated  from 
the  undissolved  osmide,  evaporated  to  expel  the  excess  of 
aqua  regia,  and  dissolved  in  water  and  hydrochloric  acid. 

'  2.  Precipitation  of  Liquids  by  Sulphuretted  Hydrogen. — - 
Liquids  obtained  as  above  are  ready  for  precipitation  by 
hydrosulphuric  acid. 

'  The  apparatus  in  which  all  the  liquids  are  precipitated 
is  composed  of  a  sulphuretted  hydrogen  gas  generator  by 
the  action  of  sulphuric  acid  on  iron  sulphide.  This  gene- 
rator communicates  with  four  or  five  large  earthenware 
jars,  holding  about  seventy  litres,  arranged  precisely  as  in 
Wolffs  apparatus.  A  special  tube  conducts  to  each  of 
them  the  vapour  destined  to  heat  the  liquid  which  they 
contain. 

'  The  whole  apparatus  is  enclosed  in  a  well-fitted  wood 
stove  placed  near  a  chimney,  with  which  it  communicates. 
As  to  the  small  quantities  of  unabsorbed  gas,  they  are 
conducted  into  the  chimney,  where  the  fire  creates  a  strong 
draught.  By  this  means,  also,  all  smell  is  avoided  during  the 
precipitation  ;  but  after  the  operation  air  is  forced  through 
the  apparatus  from  large  gasometers.  It  expels  the  hydro- 
chloric acid  which  saturates  the  mother  liquors,  and  these 
can  then  be  manipulated  free  from  smell.f 

*  This  solution  is  separately  precipitated  by  hydrosulphuric  acid.  Osmium 
sulphide  is  thus  isolated. 

t  A  carbonic  acid  generator  may  be  substituted  for  the  prasometers  and  the 
air  with  no  difference  in  the  result. 


GUYARD'S  PROCESS.  721 

'  The  experiment  is  carried  on  during  the  precipitation 
in  the  following  manner :  when  the  generator  begins  to 
disengage  gas,  the  temperature  of  the  liquids  is  raised  to 
about  70°.  This  temperature  is  maintained  for  nearly  fif- 
teen hours,  that  being  the  time  required  for  the  complete 
precipitation  of  the  sulphides,  which  collect  better  under 
the  influence  of  heat.  The  operation  is  concluded  when 
there  remains  but  a  very  slight  yellow  tint  in  the  mother 
liquor,  arising  from  the  presence  of  a  little  soluble  iridium 
sulphide.  This  mother  liquor  is  poured  from  the  precipi- 
tated sulphides  into  a  vessel  with  pieces  of  iron,  which 
takes  off  a  little  of  the  iridium.  The  sulphides  are  filtered 
through  linen  filters. 

'  3.  Purification  and  Treatment  of  the  Sulphides. — The 
mass  of  sulphides  thus  separated  from  the  iron  and  from 
all  other  bodies  not  precipitated  by  the  sulphuretted  gas, 
contains,  in  addition  to  the  sulphides  of  the  platinum 
metals,  a  large  proportion  of  sulphur  and  the  sulphides 
of  copper  and  lead.  To  get  rid  of  these  bodies,  I  have 
thought  of  concentrated  sulphuric  acid,  which  changes 
them  to  sulphurous  acid  and  sulphates,  while  it  does  not 
act  on  the  sulphides  of  the  precious  metals.  This  refining 
can  be  effected  in  an  iron  vessel ;  but  Mr.  Mat  they,  who 
neglects  nothing  to  ensure  the  certainty  and  exactness  of 
the  results,  makes  use  of  platinum. 

'  When,  after  prolonged  boiling,  no  more  sulphurous 
acid  is  given  off,  the  refining  is  complete. 

'  The  mass  of  sulphides,  diluted  with  a  quantity  of 
water,  is  thrown  on  filters,  and  thoroughly  washed,  until 
ammonia  no  longer  shows  any  trace  of  copper  or  iron  in 
the  filtered  liquid. 

'  At  this  point  the  precious  metals  are  entirely  freed 
from  iron,  which  is  so  detrimental  to  them,  and  from 
copper,  and  contain  only  a  little  lead  sulphate,  which 
separates  by  itself  during  an  ulterior  reaction.  They  are 
then,  moreover,  in  a  condition  to  be  dissolved  by  simple 
nitric  acid  or  by  aqua  regia,  and  this  is  not  their  least 
valuable  condition. 

;  Treatment  of  the  Sulphides. — The  sulphides  are  next 

3  A 


722  THE   ASSAY    OF    PLATINUM. 

dissolved  in  aqua  regia,  which  should  not  be  previously 
prepared,  because  its  action  on  sulphates  is  sudden  and 
energetic ;  it  heats  so  rapidly,  and  the  disengagement  of 
gas  is  so  great  that,  were  it  previously  prepared,  it  would 
certainly  be  thrown  from  the  vessels. 

4 1  add  then  moderately  strong  cold  nitric  acid,  and 
add  it  gradually,  because  its  action  is  strong.  A  quantity 
of  rutilant  vapours  are  disengaged.  Hydrochloric  acid  is 
added  when  the  effervescence  ceases.  It  is  then  gradually 
heated  to  boiling,  which  is  necessary  to  obtain  a  complete 
solution. 

'  The  solution  is  poured  from  the  deposited  lead 
chloride,  and  the  ordinary  method  with  sal  ammoniac  is 
used  to  separate  the  different  metals  it  contains.  Experi- 
ments on  large  quantities  of  material  have  fully  proved 
the  advantages  of  this  process.' 

Analysis  of  Osmiridium. — Wohler's  method  of  resolv- 
ing osmiridium  consists  in  passing  moist  chlorine  over 
the  ore  mixed  with  common  salt  and  heated  to  low  red- 
ness in  a  glass  or  porcelain  tube.  This  method  is  invalu- 
able in  analysis,  and  gives  excellent  results  in  working  the 
ore  upon  a  small  scale.  In  all  cases,  however,  several 
repetitions  of  the  process  are  necessary  for  complete 
resolution  or  reduction  to  a  soluble  form.  On  the  other 
hand,  it  can  scarcely  be  doubted  that  this  method  could  be 
advantageously  employed  upon  the  large  scale,  if  vessels 
of  porcelain  of  large  size  and  of  a  proper  shape  could 
be  obtained.  Such  vessels  might  be  constructed  in  the 
form  of  long  and  flattened  ellipsoids,  furnished  at  each 
extremity  with  wide  tubes  several  inches  in  length,  and 
would  be  of  great  utility  in  various  chemical  processes. 
No  process  of  fusion  with  oxidising  agents  compares  with 
Wohler's  method  in  point  of  elegance,  as  no  iron  or  other 
impurities  afterwards  to  be  removed  are  introduced  by  the 
process  itself. 

Claus's  method  of  resolving  the  ore  consists  in  fusing 
for  an  hour,  at  a  red  heat,  a  mixture  of  one  part  of  ore 
with  one  part  of  caustic  potash  and  two  of  saltpetre.  The 
fused  mass  is  to  be  poured  out.  upon  a  ^s tone,  allowed  to 


WOLCOTT   GIBBS'S   PROCESS.  723 

cool,  broken  into  small  pieces  or  powdered,  and  then 
introduced  into  a  flask,  which  is  to  be  filled  with  cold 
water  and  allowed  to  stand  for  twenty-four  hours.  The 
clear  deep  orange-red  solution  of  potassium  osrniate  and 
rutheniate  is  then  to  be  drawn  off  by  means  of  a  syphon, 
and  the  black  mass  remaining  again  washed  in  the  same 
manner.  The  finely-divided  oxidised  portion  of  the  in- 
soluble matter  may  now  be  separated  from  the  unattacked 
ore  by  diffusion  in  water  and  pouring  off,  after  the  subsi- 
dence of  the  heavier  ore.  The  unattacked  ore  is  then  to 
be  fused  a  second  time  with  potash  and  saltpetre  and 
treated  as  before.  Glaus  asserts  that  he  has  been  able  in 
this  manner  to  resolve  the  Siberian  osmiridium  com- 
pletely in  two  operations. 

Dr.  Wolcott  Gibbs,  to  whom  the  chemistry  of  the 
platinum  metals  is  so  greatly  indebted,  recommends  the 
following  process  for  the  analysis  of  osmiridium : — The 
ore,  which  is  usually  very  impure,  is  in  the  first  place 
to  be  fused  with  three  times  its  weight  of  dry  sodium 
carbonate.  The  fused  mass  after  cooling  is  to  be  treated 
with  hot  water,  to  remove  all  the  soluble  portions,  and 
then  the  lighter  portions  are  to  be  separated  by  washing 
from  the  heavy  unattacked  ore.  In  this  manner  the 
greater  part  of  the  silica  and  other  impurities  present  may 
be  removed.  A  previous  purification  of  this  kind  is  not 
indispensable,  and  may  be  omitted  altogether  when  the 
ore  is  in  plates  or  large  grains ;  but  it  is  very  desirable 
when  the  ore  is  in  fine  powder,  and  greatly  facilitates  the 
subsequent  action  of  the  oxidising  mixture.  By  cutting 
off  the  top  of  a  mercury  bottle  a  wrought-iron  crucible  is 
obtained,  in  which  600  grms.  of  osmiridium  may  be  fused 
at  one  operation  with  potash  and  saltpetre  as  above. 
There  is  usually  little  or  no  foaming,  and  if  any  occur  it 
may  easily  be  checked  by  stirring  with  an  iron  rod.  No 
sensible  quantity  of  osmic  acid  is  given  off  during  the 
process,  which  with  a  little  care  is  entirely  free  from 
danger.  In  this  manner  1,500  grms.  of  ore  have  been 
worked  up  in  a  few  hours  in  three  successive  operations. 
The  fused  mass  is  to  be  broken  into  pieces  with  a  hammer, 

3  A  2 


724,  THE   ASSAY   OF   PLATINUM. 

and  placed  in  a  clean  iron  pot.  Boiling  water,  contain- 
ing about  one-tenth  of  its  volume  of  strong  alcohol,  is 
then  to  be  added,  and  the  whole  is  to  be  boiled  over  an 
open  fire  until  the  fused  mass  is  completely  disintegrated. 
The  potassium  osmiate  is,  in  this  manner,  reduced  to 
osmite,  while  the  potassium  rutheniate  is  completely 
decomposed,  the  ruthenium  being  precipitated  as  a  black 
powder.  It  is  advantageous,  after  boiling  for  some  time, 
to  pour  off  the  supernatant  liquid  with  the  lighter  por- 
tions of  the  oxides,  and  boil  a  second  time  with  a  fresh 
mixture  of  alcohol  and  water.  In  this  manner  we  obtain 
a  solution  of  potassium  osmite,  a  large  quantity  of  black 
oxides,  and  a  heavy  black  and  coarse  powder.  This  last 
consists  chiefly  of  undecomposed  ore,  mixed  with  a  small 
quantity  of  the  iridium  oxides,  &c.,  with  scales  of  iron 
oxide  from  the  crucible,  and,  if  the  ore  has  not  been 
previously  purified,  with  the  impurities  of  the  ore  itself. 
The  greater  specific  gravity  of  this  residual  mass  renders 
it  very  easy  to  pour  off  from  it  the  mixture  of  black 
oxides  with  the  solution  of  osmite  of  potash  and  alkaline 
salts.  This  solution  with  the  suspended  powder  is  to  be 
poured  into  a  beaker  and  allowed  to  settle.  The  heavy 
black  powder  remaining  in  the  iron  pot  is  then  to  be 
perfectly  dried  over  the  fire,  and  fused  a  second  time  with 
potash  and  saltpetre  as  before.  The  fused  mass  is  to  be 
treated  exactly  as  after  the  first  fusion.  The  heavy  por- 
tions remaining  after  this  operation  may  be  fused  a  third 
time  with  the  oxidising  mixture.  When,  however,  the  ore 
has  been  previously  purified  by  fusion  with  sodium  carbon- 
ate, or  when  it  was  originally  in  the  form  of  clean  scales, 
the  heavy  portion  remaining  after  two  successive  oxidations 
will  be  found  to  consist  chiefly  of  scales  of  iron  oxide. 

The  solutions  containing  potassium  osmite  and  alka- 
line salts  are  to  be  carefully  drawn  off  by  a  syphon  from 
the  black  oxides  which  have  settled  to  the  bottom  of  the 
containing  vessels.  The  oxides  may  then  be  washed  with 
hot  water  containing  a  little  alcohol,  and  introduced  into 
a  capacious  retort.  By  this  process,  when  carefully 
executed,  no  trace  of  osmic  acid  escapes — an  advantage 


WOLCOTT   GIBBS'S   PROCESS.  725 

not  to  be  despised,  as  the  deleterious  effects  of  this  body 
upon  the  lungs  have  not  been  exaggerated,  and  too  much 
care  cannot  be  taken  to  avoid  inhaling  it. 

The  solution  of  alkaline  salts  contains  only  a  portion 
of  the  osmium  in  the  ore.  The  other  portion  exists  in  the 
mixture  of  oxide,  and  must  be  separated  by  distillation. 
For  this  purpose  the  retort  should  be  provided  with  a 
safety-tube,  passing  through  the  tubulure,  and  with  a 
receiver  kept  cold,  and  connected  by  a  wide  bent  tube 
with  a  series  of  two  or  three  two-necked  bottles  contain- 
ing a  strong  solution  of  caustic  potash  with  a  little  alcohol, 
and  also  kept  cold.  All  the  tubulures  and  connections 
must  be  made  perfectly  tight.  Strong  hydrochloric  acid 
is  then  to  be  cautiously  poured  into  the  retort,  through 
the  safety-tube,  in  small  portions  at  a  time.  The  reaction 
which  ensues  is  often  violent ;  great  heat  is  evolved,  and 
a  portion  of  the  osmic  acid  distils  over  immediately,  and 
condenses  in  the  receiver  in  the  form  of  colourless  needles. 
When  a  large  excess  of  acid  has  been  added,  the  action 
has  entirely  ceased,  and  the  retort  has  become  cold,  heat 
may  be  applied  by  means  of  a  sand-bath.  The  osmic  acid 
gradually  distils  over,  and  condenses  in  the  receiver  and 
in  the  two-necked  bottles.  Especial  care  must  be  taken 
that  the  beak  of  the  retort  is  not  too  snrall  at  the  ex- 
tremity, as  it  may  otherwise  become  completely  stopped 
up  with  the  condensed  osmic  acid.  The  same  applies  to 
the  tubes  which  connect  the  receivers  and  two-necked 
bottles.  The  distillation  should  be  continued  for  some 
time  after  osmic  acid  ceases  to  appear  in  the  neck  of  the 
retort ;  when  this  has  once  become  hot,  the  acid  condenses, 
and  passes  into  the  receiver  in  the  form  of  oily  drops. 

When  the  distillation  is  finished,  the  retort  is  to  be 
allowed  to  cool,  and  then  separated  from  the  receiver, 
which  is  to  be  immediately  closed  with  a  cork.  By  gently 
heating  the  receiver  in  a  water-bath,  the  contained  osmic 
acid  may  be  driven  over  into  the  two-necked  bottles, 
where  it  condenses  in  the  alkaline  solution,  and  is  reduced 
by  the  alcohol  to  potassium  osmite.  The  sokition  thus 
obtained  may  be  added  to  that  obtained  directly  from  the 


726  THE   ASSAY   OF   PLATINUM. 

fused  mass  of  ore,  and  on  evaporation  in  a  water-bath  and 
cooling,  will  yield  crystals  of  potassium  osmite,  the  salt 
being  but  slightly  soluble  in  strong  saline  solutions.  The 
mother  liquor  from  the  crystals  contains  only  traces  of 
osmium,  and  may  be  thrown  away  as  worthless. 

The  dissolved  portions  drawn  off  from  the  retort  have 
a  very  dark  brown-red  colour.  The  solution  is  to  be 
evaporated  to  dryness,  re-dissolved  in  hot  water  and  again 
evaporated,  after  adding  a  little  hydrochloric  acid,  and 
this  process  repeated  till  no  smell  of  osmic  acid  can  be 
perceived.  A  cold  and  saturated  solution  of  potassium 
chloride  is  then  to  be  added  in  large  excess.  This  dissolves 
the  iron  and  palladium  chlorides  which  may  be  present, 
leaving  platinum,  iridium,  rhodium,  and  ruthenium  as 
double  chlorides,  insoluble  in  a  strong  solution  of  the 
alkaline  chloride. 

The  undissolved  mass  is  to  be  well  washed  with  a 
saturated  solution  of  potassium  chloride,  which  is  prefer- 
able to  sal-ammoniac.  In  this  manner  nearly  the  whole 
of  the  iron  and  palladium  may  be  removed,  while  any 
insoluble  impurities  contained  in  the  ore  remain  with  the 
mixed  double  chlorides. 

For  the  separation  of  osmium  from  the  other  metals  of 
the  group,  the  best  plan  seems  to  be  the  one  which  is 
universally  employed,  namely,  the  volatilisation  of  the 
osmium  in  the  form  of  osmic  acid. 

Mr.  Nelson  W.  Perry  ('  Engineering  and  Mining  Jour- 
nal ')  proposes  the  following  method  for  the  assay  of 
platinum  alloys  containing  base  metal,  silver,  platinum, 
gold,  and  osmiridium. 

Charge,  platinum  alloy  200  milligrammes,  pure  silver 
150  milligrammes,  or  sufficient  to  produce  perfect  cupella- 
tion  (exact  weight). 

Wrap  charge  in  sheet  lead  and  cupel.  Weigh  button. 
Loss  =  base  metal. 

Flatten  button,  anneal,  roll  out  thin,  anneal  again,  and 
make  into  cornet  as  in  gold  bullion  assay.  Introduce 
cornet  into  parting  flask  and  part  with  concentrated 
sulphuric  acid.  Wash,  anneal,  and  weigh.  Loss  from 


NELSON  w.  PERRY'S  PROCESS.-  727 

previous  weight  =  silver  in  original  alloy  +  silver  added 
for  cupellation. 

Alloy  cornet  with  at  least  twelve  times  the  amount  of 
silver  that  there  is  platinum  present,  and  as  before,  form 
cornet,  and  part  first  with  nitric  acid,  sp.  gr.  1-16,  and 
then  nitric  acid,  sp.  gr.  T26.  Wash  thoroughly,  anneal  in 
annealing  cup,  and  weigh.  Loss  =  platinum. 

Treat  residue  with  aqua  regia,  obtain  gold  by  loss,  the 
residue  is  osmiridium. 

Time  to  complete  assay  in  duplicate,  2  hours,  45  min. 

The  quality  of  the  silver  added  should  at  least  be 
sufficient,  so  that  after  the  addition  of  the  silver  the  alloy 
will  be  to  the  gold  as  3  :  1. 

As  platinum  and  osmiridium  add  greatly  to  the  in- 
fusibility  of  the  compound,  silver  in  sufficient  quantity 
must  be  added  to  prevent  '  freezing '  and  give  a  perfect 
cupellation.  Any  large  excess  over  these  requirements  is  to 
be  avoided,  first,  because  the  residue,  after  parting,  will 
in  that  case  be  non-adherent,  and  in  a  more  or  less  fine 
state  of  subdivision,  which  may  occasion  loss  in  washing 
by  decantation;  second,  the  larger  the  button  cupelled, 
the  more  difficult  it  is  to  obtain  a  good  cupellation,  and 
the  greater  loss  of  silver  during  the  process.  It  may, 
for  this  reason,  sometimes  be  necessary  to  use  only  100 
milligrammes  of  the  alloy  for  assay  instead  of  200  milli- 
grammes as  above. 

The  cupellation  should  take  place  at  a  moderate 
temperature,  until  near  the  '  blick,'  when  the  assay  should 
be  thrust  back  into  the  hottest  part  of  the  furnace  to 
prevent  *  freezing.'  The  button  must  remain  in  the  muffle 
until  all  the  lead  is  gone. 

In  parting  with  sulphuric  acid  boil  for  several  minutes. 
In  other  respects  this  operation  is  identical  with  the  gold 
bullion  assay.  Any  large  excess  of  silver  over  twelve 
times  the  amount  of  platinum  in  alloy  is  to  be  avoided,  as 
it  causes  the  residue,  after  parting,  to  be  too  fine  and 
float,  thereby  occasioning  loss  in  washing.  Insufficient 
silver  is  even  worse,  as  the  platinum  will  then  be  only 
incompletely  dissolved. 


728 


CHAPTER  XIX. 

THE   ASSAY   OF    BISMUTH. 
,-'<^-\    L*  ,•'.  £    ,.-,:;:,,  .     .  .';,' 

THE  following  varieties  of  bismuth  ores  are  met  with,  but 
are  somewhat  rare  : — 

Native  Bismuth. 

Bismuth  Oxide. 

Bismuth  Sulphide. 

Bismuth  Persulphide. 

Cupriferous  Bismuth  Sulphide. 

Plurnbo-cupriferous  Bismuth  Sulphide. 

Plumbo-argentiferous  Bismuth  Sulphide. 

Native  Bismuth  possesses  a  tolerably  bright  metallic 
lustre  ;  its  colour  yellowish- white,  often  iridescent.  It 
fuses  in  the  candle  flame.  It  is  generally  found  in  small 
amorphous  lamellar  masses,  yet  it  occasionally  occurs  in 
acute  rhomboidal  as  well  as  cubical  and  octahedral 
crystals. 

This  substance  does  not  seem  to  form  veins  by  itself, 
but  generally  accompanies  other  minerals,  particularly 
those  of  cobalt,  nickel,  arsenic,  and  lead. 

To  within  a  recent  period  the  chief  source  of  the  com- 
mercial product  has  been  native  bismuth.  But  this 
limited  source  is  becoming  well-nigh  exhausted,  whilst  the 
demand  for  this  metal,  especially  in  a  great  state  of  purity, 
is  increasing  every  day.  It  has  thus  become  a  matter  of 
necessity  to  look  for  fresh  fields  of  exploration,  for  new 
deposits  :  and  as  bismuth  ores  of  every  description  mixed 
up  with  other  ores  of  various  kinds  are  now  used  for  the 
extraction  of  bismuth,  the  assay  of  this  metal  has  lost  some 
of  its  former  simplicity.  Mr.  Hugo  Tamm  has  done  more 
than  any  metallurgist  towards  perfecting  the  assay  of 


ASSAY   OF   BISMUTH   ORES.  729 

bismuth,  and  from  his  papers  on  this  subject  in  the 
'•  Chemical  News,'  Nos.  639  and  640,  the  following  method 
of  assay  is  condensed  : — 

Assaying  of  Bismuth  Ores. — Whenever  the  ore  to  be 
tried  is  of  a  simple  nature,  is  free  from  admixture  with 
other  ores,  and  contains  bismuth  in  the  metallic  state,  or 
in  the  state  of  sulphide,  of  oxide,  or  of  carbonate,  or,  as 
sometimes  occurs,  consists  of  a  mixture  of  oxide,  carbon- 
ate, sulphate,  and  oxy chloride,  the  assaying  of  bismuth  is 
reduced  to  the  very  simple  operation  of  mixing  the  ore  with 
as  fusible  a  flux  as  can  easily  be  obtained,  to  which  a 
reducing  substance,  generally  charcoal  powder,  is  added 
in  proper  quantity. 

It  is  of  course  useless  to  lay  down  particular  rules 
concerning  the  nature  or  the  quantity  of  the  flux,  and  of 
the  reducing  substance  to  be  employed  in  this  operation  ; 
indeed,  it  is  not  advisable  to  do  so,  and  it  is  by  far  the 
best  to  be  guided  by  the  nature  of  the  materials  at  hand, 
and  by  the  results  of  a  few  trials  with  varied  proportions 
of  flux  and  of  the  reducing  agent ;  the  aim  of  the  assayer 
being  the  highest  amount  of  metal  that  can  be  obtained  in 
a  given  instance.  Still,  one  of  the  best  fluxes,  as  well  as 
one  of  the  most  simple,  consists  of  a  mixture  of  two  parts 
of  potassium  or  sodium  carbonate,  and  one  part  of  sodium 
chloride,  to  which  a  proper  amount  of  red  argol  or  of 
potassium  cyanide  on  the  small  scale,  and  powdered 
charcoal  on  the  large  scale,  are  added. 

Assaying  of  Bismuth  in  Ores  containing  a  large  amount 
of  Copper. — The  problem  of  the  direct  separation  of  bis- 
muth from  ores  containing  large  proportions  of  copper  has 
hitherto  been  one  of  difficulty,  and  its  solution,  which  was 
of  considerable  importance,  offered  great  interest.  The 
difficulty  consisted  chiefly  in  the  fact  that  both  copper 
and  bismuth  behave,  in  nearly  every  instance,  in  an 
identical  manner  with  docimastic  reagents ;  but  Mr. 
Tamm  has  happily  hit  upon  a  most  simple  and  practical 
means  of  effecting  the  direct  separation  of  those  two 
metals. 

The  chief  kinds  of  ores  containing  both  bismuth  and 


730  THE   ASSAY   OP   BISMUTH. 

copper  are  the  bismuth-copper  pyrites  or  sulphuretted 
ores,  and  the  double  bismuth  and  copper  oxides  or  car- 
bonates, or  oxidised  ores. 

Both  kinds  of  ores  may  be,  and  generally  are,  con- 
taminated with  other  metals,  but  these  foreign  metals  con- 
stitute only,  as  a  rule,  a  small  fraction  of  the  whole,  and 
the  problem  of  their  elimination  will  be  given  further  on. 

The  reaction  upon  which  the  separation  of  bismuth 
from  copper  is  founded  consists  in  the  fact  that,  in  pre- 
sence of  alkaline  fluxes,  carbonaceous  reagents,  and,  of 
course,  among  them  .carbon  itself,  reduce  bismuth  sul- 
phide to  the  metallic  state,  while  copper  sulphide  is  not 
reduced. 

In  the  treatment  of  sulphuretted  ores,  both  metals 
being  already  in  the  state  of  sulphides,  all  that  is  required 
is  to  run  them  down  with  a  mixture  of  potassium  carbo- 
nate or  soda,  and  salt,  to  which  a  little  flowers  of  sulphur 
or  ground  sulphur,  and  charcoal  or  any  other  carbonaceous 
substance,  are  added. 

In  this  operation  metallic  bismuth  is  extracted  quite 
easily,  and  the  metal  thus  obtained  is  tolerably  free  from 
copper.  It  is  recommended  to  add  a  little  sulphur  in 
order  to  insure  a  complete  sulphurisation  of  copper  during 
the  whole  of  the  operation,  and  especially  to  prevent  any 
desulphurisation  of  copper  by  the  alkali,  and,  consequently, 
to  prevent,  as  much  as  possible,  this  metal  from  being 
reduced. 

With  oxidised  ores  the  operation  is  very  similar  in 
every  respect  to  the  one  just  described,  and  it  differs  from 
it  only  in  the  amount  of  sulphur  used,  which  is  greater 
in  this  instance,  since  the  whole  of  the  metals  have  to  be 
sulphurised. 

Three  parts  of  the  ore  are  mixed  with  from  two  to 
three  parts  of  a  flux  composed  of : — • 

Sodium  carbonate      f  ,.    .     ;       . .    J.  .    Sparta 

Salt      .      ...,".    ,.,.     ...   ,,    ,_.    .  2     „ 

Sulphur        .        .      "«*'..''''•   ';  "  .2    „ 

Charcoal  powder  .'  ,..:..     '  ,« "  •     1     » 

Both  the  composition  of  the  flux  and  the  amount  to  be 
used  may  be  altered  with  advantage  to  suit  each  particular 


ASSAYING   BISMUTH    ORES   WITH   MUCH   COPPER.  731 

case.  A  few  synthetical  trials,  in  the  hands  of  a  person 
accustomed  to  metallurgical  operations,  are  all  that  are 
required  to  make  the  best  use  of  this  reaction. 

In  general,  it  is  to  be  observed  that  the  amount  of  flux 
and  of  reagents  required  for  the  assaying  may  be  con- 
siderably reduced  when  the  operation  is  carried  on  on  a 
larger  scale.  On  the  other  hand,  it  is  scarcely  worth 
while  mentioning  that,  in  the  operation  of  assaying,  potas- 
sium cyanide  forms  an  admirable  substitute  for  carbon. 

During  the  process  of  extracting  bismuth  by  means  of 
sulphur  and  carbon  there  is  a  loss  of  about  8  per  cent,  of 
the  bismuth  contained  in  the  ore.  This  loss  is  unavoidable, 
but  there  is  a  more  than  proportionate  loss  of  the  metals 
arsenic,  antimony,  and  lead,  which  in  this  operation  are 
reduced  with  bismuth,  and  the  crude  metal  obtained  by 
this  process  is  not  so  impure  as  the  corresponding  metal 
obtained  by  the  direct  reduction  of  the  oxidised  ores  ; 
besides  the  whole  of  the  copper  remains  in  the  slag. 

Whenever  the  sulphur-carbon  process  is  employed,  the 
use  of  iron  stirrers  must  be  carefully  avoided,  for  the  reason 
that  copper  sulphide  is  rapidly  reduced  to  the  metallic  state 
by  this  metal,  especially  in  the  presence  of  alkalies. 

This  process  for  the  separation  of  bismuth  from  copper 
will  be  found  chiefly  useful  and  important  for  the  separa- 
tion of  bismuth  in  minerals  containing  large  quantities  of 
copper.  When,  on  the  contrary,  this  metal  exists  only  in 
smaller  proportions,  it  is  more  advantageous  to  run  down 
the  whole  of  the  metals,  and  to  separate  them  afterwards 
in  the  special  operations  of  refining.  But  it  is  recom- 
mended that  the  sulphur-carbon  process  be  used  for  the 
*  treatment  of  the  somewhat  abundant  ores  of  bismuth 
formed  of  bismuth  and  lead  oxides,  and  small  proportions 
of  arsenious  acid  and  antimonious  acid,  with  a  little  copper 
oxide  ;  for  there  is  as  yet  no  direct  means  of  smelting  pure 
bismuth  from  ores  containing  large  proportions  of  lead, 
but  it  has  been  observed  that  bismuth  extracted  by  the 
sulphur  process  contains  less  lead  than  the  corresponding 
metal  obtained  direct  from  the  oxidised  ore.  The  same 
remark  applies  to  arsenic  and  antimony,  and  this  is  in 


732  THE   ASSAY   OF   BISMUTH. 

accordance  with  the  behaviour  of  the  sulphides  of  these 
metals  with  alkaline  sulphides. 

Refining  Crude  Bismuth. — The  various  ores  of  bismuth 
above  described,  whether  sulphuretted  or  oxidised,  are 
seldom  formed  of  bismuth  and  iron  only,  or  of  only 
bismuth,  copper,  and  iron.  They  nearly  always  are  con- 
taminated by  various  proportions  of  lead,  arsenic,  or  anti- 
mony, metals  which  are  reduced  with  bismuth,  partially  at 
least,  whatever  process  has  been  used  for  the  extraction  of 
bismuth,  and  besides,  the  metal  obtained  by  the  sulphur 
process  from  copper  bismuth  ores  still  contains  a  small 
quantity  of  copper,  which  it  is  important  to  remove. 

Bismuth  extracted  by  any  process  is  so  generally  free 
from  iron  that  no  notice  need  be  taken  of  this  metal,  which 
remains  wholly  in  the  slags. 

The  fracture  of  good  bismuth  and  that  of  its  various 
alloys  is  so  characteristic  that  it  is  not  often  necessary  to 
have  recourse  to  tests  in  order  to  determine  what  particular 
processes  will  have  to  be  used  for  the  refining  of  the  crude 
metal. 

Pure  bismuth  is  tougher  than  most  of  its  alloys.  Its 
fracture  is  bright,  and  it  possesses  a  fine  reddish  colour. 
Bismuth  containing  arsenic  gives  a  beautiful  fracture  con- 
sisting of  large  laminae  of  a  whiter  colour  than  that  of  pure 
bismuth.  Copper  mixes  with  bismuth  without  alloying 
with  it,  and  is  almost  always  discernible.  The  fracture  of 
bismuth  containing  antimony  is  dull  and  is  mostly  composed 
of  very  small  crystals.  Lead  does  not  prevent  bismuth  from 
crystallising  in  large  crystals,  but  these  crystals  are  studded 
all  over  with  fine  crystals.  Sulphur  imparts  a  black  tinge 
to  metallic  bismuth. 

To  these  appearances,  which  almost  suffice  to  an  ex- 
perienced eye,  may  be  added  a  few  simple  tests. 

It  is  difficult  to  detect  arsenic  in  the  presence  of  a  large 
quantity  of  bismuth  by  means  of  reagents,  and  the  most 
simple  way  of  detecting  this  substance  is  to  heat  the  bis- 
muth on  charcoal,  with  the  oxidising  fiame  of  the  blow- 
pipe. Very  small  quantities  of  arsenic  may  be  detected 
by  the  garlic  odour  evolved. 


PURIFICATION   OF   BISMUTH.  733 

To  detect  copper  the  metal  is  dissolved  in  nitric  acid, 
the  solution  is  supersaturated  by  ammonia,  and  filtered. 
The  blue  colour  of  the  filtrate  indicates  the  presence  of 
copper. 

When  bismuth  dissolves  in  strong  nitric  acid,  with  the 
formation  of  a  cloudy  white  precipitate  which  does  not 
disappear  on  the  addition  of  water,  it  is  because  antimony 
is  present. 

When  bismuth  dissolves  in  strong  nitric  acid,  with  the 
formation  of  a  very  white  granular  or  crystalline  precipi- 
tate which  dissolves  freely  on  the  addition  of  water,  the 
presence  of  lead  is  indicated. 

But  to  detect  with  absolute  certainty  the  presence  of 
even  very  small  proportions  of  lead,  the  metal  i?  dissolved 
in  nitric  acid.  The  solution  is  supersaturated  with  am- 
monia, and  re-acidulated  with  the  smallest  amount  of  hydro- 
chloric acid  which  will  give  a  clear  liquor.  This  liquor  is 
then  precipitated  by  a  large  excess  of  boiling  water.  Water 
must  be  added  until  no  further  precipitation  takes  place. 
The  whole  is  then  filtered,  and  the  filtrate  is  saturated  with 
a  mixture  of  ammonia  and  ammonium  carbonate ;  when 
a  yellowish-white  precipitate  is  formed  it  is  because  lead 
exists  in  the  bismuth. 

It  may  be  useful  to  submit  the  metal  to  be  refined  to 
these  various  tests  in  order  to  ascertain  beforehand  which 
refining  process  should  be  used.  But  it  is  essential  to  apply 
each  test  to  the  refined  metal,  so  as  to  verify  its  degree  of 
purity. 

PURIFICATION   OF   THE   REDUCED   BISMUTH. 

Purification  of  Bismuth  from  Arsenic. — The  separation 
of  bismuth  from  arsenic  is  founded  on  the  almost  absolute 
want  of  affinity  of  bismuth  for  iron,  on  the  readiness  with 
which  arsenic  combines  with  iron,  and  on  the  fact  that  the 
iron  arsenide  thus  formed  does  not  alloy  with  bismuth. 
This  operation  is  conducted  in  the  following  manner : — 

Bismuth  is  melted  at  a  relatively  high  temperature,  at 
a  bright  red  heat,  under  cover  of  borax  or  flux,  to  avoid 
loss  of  bismuth  by  volatilisation,  and  strips  of  iron  are 


734  THE   ASSAY    OF   BISMUTH. 

plunged  into  the  molten  metal.  Iron  is,  according  to  the 
technical  expression,  rapidly  '  eaten  away,'  forming  iron 
arsenide,  which  rises  to  the  surface  of  the  metal. 

When  it  is  ascertained  that  fresh  pieces  of  iron  are  no 
]onger  attacked,  the  whole  is  allowed  to  cool.  The  iron 
arsenide  sets  rapidly,  and  the  bismuth,  which  is  still  fluid, 
is  poured  out  of  the  crucible  into  moulds.  Singularly 
enough,  this  process,  which  succeeds  in  perfection  for  the 
separation  of  arsenic,  is  valueless  when  applied  to  the 
separation  of  bismuth  from  antimony ;  although,  be  it 
noticed,  the  affinity  of  this  metal  for  iron  is  very  great. 
Some  antimony  is  removed  by  this  process,  but  part  of  it 
only,  and  it  must  be  admitted  that  bismuth  has  as  much, 
Or  more,  affinity  for  antimony  than  iron. 

Purification  of  Bismuth  from  Antimony. — The  best  way 
of  separating  the  two  metals  is  to  melt  the  alloy  with  a 
quantity  of  bismuth  oxide,  equal  to  two  and  a  half  or  three 
times  the  weight  of  the  antimony  contained  in  the  alloy. 
The  bismuth  oxide  is  instantaneously  reduced  to  the 
metallic  state,  and  antimony  is  liberated  under  the  form  of 
antimony  oxide,  which  combines  with  a  little  bismuth  oxide, 
and  floats  on  the  surface  of  the  pure  metal,  whence  it  can 
easily  be  removed. 

This  operation  must  be  performed  in  clay  crucibles,  and 
both  carbon  and  iron  must  be  carefully  excluded,  to  avoid 
any  reduction  of  antimony  oxide.  The  least  traces  of 
antimony  may  be  removed  by  this  process  without  any 
difficulty  whatever. 

Purification  of  Bismuth  from  Copper. — When  bismuth 
ores  contain  only  a  small  percentage  of  copper,  and  when 
the  ores  are  oxidised  ores,  it  is  advantageous  to  reduce 
them  at  once  by  carbon  and  fluxes,  without  going  through 
the  sulphurising  process  ;  and,  as  a  matter  of  course,  all 
the  copper  is  alloyed  with  the  bismuth. 

On  the  other  hand,  bismuth  extracted  from  copper 
ores  by  the  sulphur  process  contains,  even  in  the  best  con- 
ducted operation,  a  certain  proportion  of  copper  which 
must  be  removed.  This  elimination  has  hitherto  presented 
very  great  difficulties,  and  could  not  be  effected  without 


PURIFICATION    OF   BISMUTH.  735 

losing  a  large  amount  of  bismuth.  Mr.  Tamm  has,  how- 
ever, devised  the  following  method,  by  melting  the  alloy 
with  potassium  sulphocyanide. 

The  sulphocyanide  is  prepared  during  the  process  of 
refining,  by  mixing  together  eight  parts  of  potassium  cya- 
nide and  three  parts  of  flowers  of  sulphur.  One  part  of 
this  mixture  is  thrown  on  to  sixteen  parts  of  the  metal 
melted  at  a  low  temperature. 

A  reaction  soon  takes  place,  by  which  the  mass  of  the 
metal  is  brought  to  a  bright  red  heat,  and,  at  the  same 
time,  the  sulphocyanide  begins  to  burn  vividly,  throwing, 
in  every  direction,  showers  of  scintillating  sparks  emitting 
a  blue  light. 

The  crucible  is  covered  over,  and  great  care  must  be 
taken  to  prevent  the  heat  from  rising  above  the  burning 
point  of  the  sulphocyanide,  a  temperature  at  which  bismuth 
sulphide  begins  to  volatilise. 

The  reaction  is  allowed  to  exhaust  itself,  and,  when 
all  is  quiet,  and  after  the  metal  has  been  well  stirred  with 
a  clay  stirrer  (iron  must  be  avoided),  the  flux  is  allowed  to 
set,  and  the  metal,  which  is  still  fluid,  is  poured  out  into 
moulds. 

Purification  of  Bismuth  from  Sulphur. — The  metal  ob- 
tained in  the  above  operation  contains  some  sulphur.  To 
remove  this  substance,  the  metal  is  melted  with  iron  or 
carbon ;  the  separation  is  thus  effected  easily. 

The  several  processes  here  proposed  are  chiefly  useful 
for  the  refining  of  bismuth  alloyed  with  one  metal. 

There  is  no  dry  method  of  refining  by  one  process 
bismuth  alloyed  with  several  metals;  but  the  succes- 
sive use  of  these  different  methods  can  safely  be  recom- 
mended. 

Copper  should  be  removed  first,  for  the  reason  that 
some  lead,  antimony,  and  arsenic  are  eliminated  at  the  same 
time. 

Bismuth  should  next  be  freed  from  antimony,  and, 
lastly,  from  arsenic  and  sulphur. 

Herr  Thurach  ('  Journal  fur  Prakt.  Chemie,'  P.  S.  14, 
315)  precipitates  with  sulphuretted  hydrogen  from  a  hot 


736  THE   ASSAY   OF   BISMUTH. 

solution,  washes  with  hot  water,  heats  for  a  considerable 
time  to  200-300°  in  a  covered  crucible,  roasts  in  the  open 
crucible,  and  finally  ignites  strongly  and  weighs  as  bismuth 
oxide. 

VOLUMETRIC   ASSAY   OF   BISMUTH. 

Mr.  E.  W.  Pearson  has  given  the  following  process  for 
the  Volumetric  Assay  of  Bismuth. 

Preparation  of  Standard  Solution. — '7135  grain  of 
pure  crystallised  potassium  bichromate  is  dissolved  in 
100  grains  of  water.  Call  this  solution  the  bichrome  test 
A,  In  a  similar  way,  prepare  a  second  solution,  one-tenth 
the  strength  of  bichrome  test  A  ;  '07135  grain  of  potassium 
bichromate  dissolved  in  100  grains  of  water,  will  furnish 
such  a  solution  ;  call  it  the  bichrome  test  B.  Bichrome 
test  C,  one-tenth  the  strength  of  solution  B,  is  also  prepared 
by  dissolving  -007135  grain  of  the  potassium  bichromate  in 
100  grains  of  water. 

These  figures  can  be  multiplied  to  any  convenient 
number.  These  solutions  will  contain  potassium  bichro- 
mate, in  100  grains  of  bichrome  test  A,  equal  to  1  grain  of 
bismuth  ;  in  100  grains  of  bichrome  test  B,  equal  to  O'l 
grain  of  bismuth ;  and  in  100  grains  of  bichrome  test  C, 
equal  to  '01  grain  of  bismuth. 

The  bismuth  should  be  in  the  form  of  nitrate,  and  the 
solution  kept  hot  during  the  experiment,  as  the  precipi- 
tated chromate  collects  more  readily  then  ;  after  com- 
plete precipitation  of  the  bismuth  the  solution  will  exhibit  a 
characteristic  colour,  produced  by  excess  of  the  bichromate 
of  potash. 

By  employing  a  standard  solution  of  bismuth  it  has 
been  ascertained  that  71'35  parts  of  potassium  bichromate 
are  required  to  combine  with  100  parts  of  bismuth. 

For  alloys  of  tin,  lead,  and  bismuth  (fusible  metal)  the 
alloy,  finely  divided,  is  oxidised  in  a  roomy  flask  with 
nitric  acid,  the  liquid  is  somewhat  diluted,  supersaturated 
with  ammonia,  and  digested  for  a  long  time  and  with  fre- 
quent agitation  with  ammonium  hydrosulphide,  to  which 


VOLUMETRIC   ASSAY    OF   BISMUTH.  737 

a  little  sulphur  has  been  added.  The  tin  is  thus  dissolved 
as  sulphide.  The  lead  and  bismuth  sulphides  are  filtered 
off  and  washed  with  cold  water.  The  liquid  containing 
the  tin  sulphide  is  slightly  supersaturated  with  dilute  sul- 
phuric acid  and  very  gently  warmed,  the  vessel  being 
loosely  covered  with  paper  tUl  the  odour  of  sulphuretted 
hydrogen  has  disappeared.  The  yellow  tin  sulphide  is 
washed  on  a  filter  with  cold  water,  and  treated  as  directed 
for  the  analysis  of  tin  ore. 

The  lead  and  bismuth  sulphides  are  dried,  detached  from 
the  filter,  which  is  incinerated  with  the  usual  precaution5', 
the  whole  digested  with  nitric  acid,  and  the  solution  con- 
centrated at  last  with  the  addition  of  hydrochloric  acid  till 
it  is  reduced  to  a  small  bulk,  and  the  greatest  part  of  the 
lead  is  separated  as  chloride.  The  proportion  of  acid  must 
be  so  large  that  the  liquid  is  not  rendered  turbid  by  a 
slight  addition  of  water.  Sulphuric  acid  is  added,  and  the 
whole  let  stand,  but  with  frequent  stirring.  After  the  lead 
chloride  has  been  converted  into  sulphate  a  little  alcohol 
of  0-80  sp.  gr.  is  added,  and  the  whole  brought  upon 
a  weighed  filter,  where  it  is  washed,  first  with  alcohol 
acidulated  with  hydrochloric  acid,  and  afterwards  with 
water. 

In  the  filtrate  all  the  bismuth  is  precipitated  as  basic 
chloride  by  the  addition  of  water  in  large  excess,  and  fil- 
tered off  (the  filtrate  being  tested  with  sulphuretted  hydro- 
gen), washed  with  cold  water,  dried,  and  melted  at  a 
moderate  heat  with  four  parts  potassium  cyanide  in  a 
covered  porcelain  crucible  (Bamnielsberg). 

Mr.  M.  Patteson  Muir  ('  Chem.  News,'  April  27,  1877) 
finds  the  following  solution  a  most  sensitive  test  for  bis- 
muth : — 12  grms.  crystalline  tartaric  acid,  and  4  grms. 
stannous  chloride  are  dissolved  in  caustic  potash,  producing 
a  clear  liquid  of  a  decidedly  alkaline  reaction,  which 
should  remain  clear  at  60°  to  70°  C.  To  the  liquid  to  be 
tested  is  added  a  considerable  quantity  of  tartaric  acid. 
It  is  warmed  and  made  alkaline  with  caustic  potash.  A 
few  c.c.  of  the  stannous  chloride  solution  (called  from  its 

3    B 


738  THE   ASSAY    OF   BISMUTH. 

first  discoverer  Schneider's  reagent)  are  added,  and  the 
liquid  warmed  to  60°  to  70°  C.  for  a  few  minutes.  If  bis- 
muth is  present  to  the  extent  of  one  parkin  210,000  parts, 
a  brownish- black  colour  is  produced.  Mercury  must  be 
absent ;  copper  and  manganese  interfere  slightly. 


739 


CHAPTEE  XX. 

THE   ASSAY   OF   CHROMIUM, 

THE  principal  ore  of  this  metal  which  occurs  in  commerce 
is  known  as  chrome  iron,  or  chrome  iron  ore.  It  is  found 
in  amorphous  masses  of  a  brownish-black  colour,  approach- 
ing an  iron  grey.  Its  fracture  is  uneven,  sometimes  la- 
mellar ;  and  its  powder  is  greyish. 

The  two  following  analyses  will  give  a  general  idea  of 
its  composition  : — 


Chromium  oxide 
Feme  oxide 
Alumina     .        . 
Silica 

.    36-0 
.     37-0 
.    21-5 
5-0 

43-7 
34-7 
20-3 
20 

f 

"995 

100-7 

Assay  of  Chrome  Iron  Ore. 

Chrome  iron  ore,  like  native  tin  oxide,  is  very  difficultly 
decomposable  by  ordinary  reagents. 

Dr.  Gen th,  of  Philadelphia,  who  has  had  much  experi- 
ence in  the  analysis  of  chrome-iron  ore,  gives  the  following 
process  ;  it  is  very  trustworthy,  although  long  and  some- 
what tedious. 

Of  the  chrome  ore,  reduced  to  an  impalpable  powder, 
put  0'5  gramme  in  a  platinum  crucible  about  2  inches 
high,  nearly  1|  inch  wide,  and  holding  52  grammes  of 
water,  and  place  upon  it  6  grammes  of  pure  fused  potas- 
sium bisulphate,  and  heat  with  the  greatest  care  for  about 
15  minutes,  at  a  temperature  scarcely  above  the  fusing 
point  of  the  bisulphate ;  then  the  heat  is  gradually  raised, 
but  not  higher  than  to  make  the  bottom  of  the  crucible 
red  hot,  and  kept  at  this  temperature  from  15  to  20 
minutes.  Never  permit  the  mass  to  rise  to  half  the  height. 

3  B  2 


740  THE   ASSAY   OF   CHROMIUM. 

of  the  crucible.  (If  the  fusion  with  potassium  bisulphate 
is  done  too  rapidly  a  portion  of  the  analysis  is  very  apt  to 
be  lost  by  spattering,  from  the  escape  of  sulphurous  acid, 
resulting  from  the  oxidation  of  the  ferrous  oxide  by  the 
sulphuric  acid.)  The  mass  begins  now  to  fuse  quietly, 
and  vapours  of  sulphuric  acid  go  off  more  freely  ;  it  should 
then  be  kept  at  a  red  heat  for  about  twenty  minutes,  and 
the  heat  next  raised  as  high  as  necessary  to  drive  off  the 
second  equivalent  of  sulphuric  acid,  and  even  to  decom- 
pose a  portion  of  the  iron  and  chromium  sulphates.  To 
the  fused  mass  add  about  three  grammes  of  pure  sodium 
carbonate,  and  fuse  the  mixture,  and  then,  by  degrees, 
keeping  the  temperature  for  about  one  hour  at  a  dull  red 
heat,  about  the  same  quantity  of  saltpetre  ;  next  heat  for 
fifteen  minutes  at  a  bright  red  heat.  The  fused  mass  is 
dissolved  in  boiling  water,  filtered  whilst  boiling,  and 
washed  with  boiling  water. 

The  insoluble  residue,  containing  the  greater  portion  of 
the  silicic  acid,  titanic  acid,  and  alumina,  the  ferric  oxide, 
zirconia,  and — if  the  fusion  has  been  conducted  at  a  tem- 
perature sufficiently  high  to  convert  the  saltpetre  into 
caustic  potash,  and  the  above  precautions  have  been  used 
— all  the  magnesia,  is  re-dissolved  in  dilute  warm  hydro- 
chloric acid,  which  generally  dissolves  it  readily  and  com- 
pletely, and  rarely  leaves  undecomposed  ore  behind  ;  but 
if  so,  this  residue  must  invariably  be  fused  in  a  small  cru- 
cible as  before,  adding,  after  the  separation  of  the  insoluble 
portion,  the  solution  containing  the  small  quantity  of 
chromic  acid  to  the  first  filtrate.  (The  certainly  less 
troublesome  method,  to  deduct  the  insoluble  portion  from 
the  original  weight,  is  bad  ;  such  residues  have  never  the 
composition  of  the  original  ore.)  The  filtrate  contains  the 
whole  quantity  of  the  chromium  as  chromic  acid,  some- 
times a  trace  of  manganic  acid,  small  quantities  of  silicic 
acid,  alumina,  and  rarely  titanic  acid.  To  this  solution 
add  an  excess  of  ammonium  nitrate,  and  evaporate  over  a 
water-bath  nearly  to  dry  ness,  and  until  all  the  liberated 
ammonia  has  been  expelled.  The  precipitate,  remaining 
on  addition  of  water,  contains  the  silicic  acid,  titanic  acid, 


ASSAY   OF   CHROME   IRON   ORE.  741 

alumina,  and  manganic  oxide,  which  had  gone  into  solution 
with  the  chromic  acid ;  it  is  filtered  off,  and  the  filtrate 
made  strongly  acid  with  sulphurous  acid,  carefully  heated 
to  boiling,  precipitated  with  a  slight  excess  of  ammonia, 
boiled  for  a  few  minutes,  and  filtered.  Dr.  Genth  says  he 
formerly  acidulated  the  chromic  acid  solution  by  hydro- 
chloric acid  and  then  added  sulphurous  acid,  but  he  several 
times  observed  that,  although  an  excess  of  sulphurous 
acid  had  been  used,  a  small  portion  of  the  chromic  acid 
escaped  reduction,  the  filtrate  from  the  ammonia  pre- 
cipitate being  yellow.  He  has  in  vain  tried  to  find  the 
reason  for  this  singular  behaviour.  Since  using  sul- 
phurous acid  only,  he  has  never  been  troubled  with  any- 
thing similar. 

It  is  exceedingly  difficult  to  wash  out  the  chromic 
oxide ;  it  succeeds  best  in  the  following  way : — After  the 
precipitate  has  settled,  the  clear  liquid  is  passed  through 
the  filter,  then  boiling  water  is  added  to  the  precipitate, 
and  after  settling,  the  supernatant  liquid  is  filtered  ;  the 
precipitate  then  is  put  on  the  filter,  and  washed  twice  or 
three  times  with  boiling  water ;  it  is  then  washed  back  again 
into  the  dish  and  boiled  with  water  until  the  little  lumps 
which  clog  together  are  completely  broken  up,  and  it  is 
then  filtered  again,  and  this  operation  repeated  until  the 
wash-waters  do  not  show  the  presence  of  any  sulphates 
when  tested  with  barium  chloride.  The  precipitate  is 
then  dried  and  burned.  No  matter  how  well  it  may  have 
been  washed,  it  almost  invariably  contains  minute  quanti- 
ties of  alkalies,  in  the  presence  of  which  a  little  chromic 
oxide  is  converted  into  chromic  acid.  The  ignited  pre- 
cipitate is  therefore  put  into  a  dish,  boiled  with  water,  a 
few  drops  of  sulphurous  acid  added,  precipitated  by  am- 
monia, filtered,  washed,  dried,  ignited,  and  weighed. 

n  this  manner  the  chromic  oxide  is  obtained  quite 
pure,  and  repeated  analyses  of  the  same  sample  of  ore 
never  vary  0*25  per  cent,  of  chromic  acid. 

Mr.  O'Neill  uses  a  volumetric  method  to  estimate  the 
chromic  acid,  depending  upon  the  capability  of  sulphurous 
acid  to  deoxidise  chromic  acid  at  the  ordinary  temperature 


742  THE   ASSAY   OF    CHROMIUM. 

in  the  presence  of  free  sulphuric  acid.  Prepare  a  strong 
solution  of  sodium  bisulphite,  by  passing  sulphurous  acid 
through  caustic  soda  to  saturation,  and  then  make  it 
alkaline  with  caustic  soda,  so  as  to  have  a  neutral  sulphite, 
which  is  less  readily  oxidised  by  keeping  than  the  bisulphite. 
Use  a  dilute  solution  made  from  this  concentrated  sulphite, 
of  such  a  strength  that  one  grain  of  pure  potassium  bichro- 
mate requires  about,  and  not  less  than,  200  grains  measure 
of  the  sulphite  to  deoxidise  it.  The  value  of  the  sulphite 
must  be  determined  for  every  operation,  since  it  is  con- 
tinually absorbing  oxygen.  This  is  done  twice  by  weighing 
out  three  grains,  and  four  grains  of  pure  bichromate,  dis- 
solving each  of  them  in  ten  ounces  of  water  and  acidulating 
freely  with  sulphuric  acid,  then  adding  the  sulphite  from 
the  burette,  with  continual  stirring,  until  the  chromic  acid 
is  destroyed.  The  stopping-point  may  be  ascertained  by 
the  colour  when  one  is  accustomed  to  the  reaction,  but 
even  an  experienced  eye  will  often  be  glad  of  additional 
evidence.  A  mixture  of  potassium  iodide  and  boiled 
starch,  slightly  acidulated,  forms  a  delicate  test ;  it  has 
usually  a  faint  colour,  which  is  even  preferable  to  a  colour- 
less mixture.  An  exceedingly  small  quantity  of  chromic 
acid  developes  the  blue  colour  in  spots  of  this  mixture, 
and  a  very  slight  excess  of  sulphite  makes  it  colourless. 
One  division  of  the  sulphite  test-liquor,  or  0*05  grain  of 
potassium  bichromate  in  twelve  ounces  of  water,  easily 
and  quickly  influences  the  test  mixture.  The  chromate 
from  the  chrome  ore  is  tested  in  the  same  manner,  and  the 
quantity  of  chromium  oxide  or  chromic  acid  calculated 
from  the  equivalents  of  potassium  bichromate.  The  tenth 
of  a  grain  more  than  five  is  taken  to  allow  for  all  losses, 
and  the  results  are  multiplied  by  twenty  for  the  per- 
centage. 151  of  potassium  bichromate  is  reckoned  equi- 
valent to  80  of  green  oxide  of  chromium,  and  104  of 
chromic  acid.  A  determination  can  be  made  by  this 
process  in  three  or  four  hours,  and  a  double  determination 
in  a  little  longer  time. 

Dr.  Wolcott  Gibbs  has  shown  that  chrome-iron  ore 
may  be  completely  resolved  by  fusion  with  fluohydrate  of 


WOLCOTT    GIBBS  S   PROCESS.  743 

potassium  fluoride.  In  this  and  in  all  similar  applications 
of  the  fluohydrate  it  is  best  to  evaporate  the  finely-pul- 
verised mineral  to  dryness  with  a  concentrated  solution  of 
the  salt.  On  subsequently  heating  to  low  redness,  the 
resolution  of  the  mineral  is  effected  with  the  utmost  ease, 
a  portion  of  the  chromium  being  usually  oxidised  to 
chromic  acid  by  the  oxygen  of  the  air.  After  expelling 
the  fluorine  by  heating  the  fused  mass  with  sulphuric  acid, 
the  remaining  mass  is  dissolved  in  water,  rendered  nearly 
neutral  by  a  solution  of  sodium  carbonate,  and  sodium 
acetate  is  added  in  excess.  A  current  of  chlorine  gas,  or 
a  solution  of  chlorine  water,  then  readily  converts  the 
whole  of  the  chromium  present  into  chromic  acid,  espe- 
cially when  the  solution  is  hot,  and  when  it  is  kept  nearly 
neutral  by  the  occasional  addition  of  sodium  carbonate. 
The  excess  of  chlorine  is  easily  got  rid  of  by  boiling. 

The  iron  and  alumina  may  then  be  precipitated  to- 
gether by  boiling  the  solution  in  the  presence  of  excess  of 
sodium  acetate.  It  is  more  convenient  and  equally  accu- 
rate to  neutralise  the  solution  with  ammonia,  separate  the 
ferric  oxide  by  filtration,  and  determine  the  chromium  in 
the  filtrate  by  reduction  and  precipitation  with  ammonia. 

For  the  technical  determination  of  chromium  in  chro- 
mite,  Mr.  Clarke  fuses  with  cryolite  and  potassium  bisul- 
phate.  The  mass  is  then  treated  with  a  little  strong 
hydrochloric  acid,  and  allowed  to  digest  for  about  ten 
minutes.  Then  upon  boiling  with  water,  the  whole  dis- 
solves. The  solution  should  then  be  neutralised,  sodium 
acetate  added,  and  the  chromium  oxidised  to  chromic  acid 
by  a  current  of  chlorine  gas,  or  by  boiling  with  sodium 
hypochlorite  solution.  The  chromium  may  then  be  sepa- 
rated from  other  substances,  as  directed  by  Dr.  W.  Gibbs. 
When  chromite  is  fused  with  potassium  bisulphate  and 
cryolite,  and  saltpetre  is  added  to  the  mass,  as  soon  as  clear 
fusion  is  obtained,  the  chromium  is  nearly  all  oxidised  to 
chromic  acid.  If  the  mass  be  boiled  with  a  solution  of 
sodium  carbonate,  and  the  liquid  filtered,  a  filtrate  is 
obtained  which  contains  nearly  all,  but  not  quite  all,  the 
chromium  as  alkaline  chromates,  free  from  iron  or  alumina ; 


744  THE   ASSAY    OF   CHROMIUM. 

but  invariably  the  residue  upon  the  filter  contains  traces 
of  chromium.  When  chromite  is  fused  with  the  acid 
potassium  fluoride,  a  part  of  the  chromium  is  usually 
oxidised  to  chromic  acid  by  the  oxygen  of  the  air  ;  and  in 
one  case  that  came  under  Mr.  Clarke's  observation,  when 
he  heated  the  resulting  mass  with  sulphuric  acid,  red  fumes 
were  given  off,  which  were  probably  the  so-called  chromium 
terfluoride. 

When  potassium  bisulphate  alone  is  used  for  the  de- 
composition of  chromite,  &c.,  it  is  necessary  that  the 
mineral  should  be  reduced  to  extremely  fine  powder ;  but 
when  the  mixture  of  bisulphate  and  fluoride  is  employed, 
although  the  mineral  should  be  in  fine  powder,  such  an 
extreme  state  of  subdivision  is  by  no  means  required,  and 
thus  much  labour  is  saved. 

Determination  of  Chromium  by  means  of  Standard 
Solution. — This  process  is  the  converse  of  the  determination 
of  iron  by  means  of  solution  of  potassium  chromate. 

The  chrome  ore  is  treated  with  potassium  nitrate  and 
sodium  carbonate,  as  above  described  ;  and  the  solution  of 
potassium  chromate  so  obtained  has  an  excess  of  hydro- 
chloric acid  added  to  it. 

It  is  stated  at  page  321,  under  the  head  of  Iron  Assay 
by  Standard  Solution,  that  100  parts  of  metallic  iron  cor- 
respond to  and  are  represented  by  88 '6  grains  of  potassium 
bichromate.  Now  88 -6  grains  of  potassium  bichromate 
contain  32-96  grains  of  chromium  ;  therefore  100  grains  of 
iron  are  equal  to  32-96  of  chromium.  From  these  data  a 
standard  solution  can  be  readily  made  :  thus — Dissolve  50 
grains  of  harpsichord  wire  in  excess  of  hydrochloric  acid  ; 
place  the  solution  in  a  burette,  and  fill  up  to  100  on  the 
instrument  with  water,  and  well  mix :  it  is  now  evident 
that  every  division  of  the  burette  will  equal  or  represent 
-1648  grain  of  chromium.  The  assay  is  now  thus  proceeded 
with  : — Gradually  add  the  standard  solution  of  iron  to  the 
solution  of  potassium  bichromate  acidulated  with  hydro- 
chloric acid,  until  a  drop  of  the  solution  mixed  with  a  drop 
of  solution  of  potassium  ferrocyanide  gives  a  pale  blue 
colour :  a  slight  excess  of  ferrous  oxide  is  then  present, 


DETERMINATION    OF   CHROMIUM   IN   IRON   AND   STEEL.       745 

showing  that  all  the  chromic  acid  has  been  reduced  to  the 
state  of  chromium  oxide.  Now  observe  how  many  divi- 
sions of  the  iron  solution  have  been  required,  and  multiply 
them  by  -1648  :  the  resulting  number  will  represent  the 
amount  of  metallic  chromium  in  the  sample  submitted  to 
assay. 

For  the  determination  of  chromium  in  iron  and  steel 
Mr.  J.  0.  Arnold  (<  Chem.  News,5  Dec.  10,  1880,  p.  285) 
weighs  out  from  1  to  5  grms.  of  steel  (in  drillings)  accord- 
ing to  the  amount  of  chromium  present  (this  may  be 
ascertained  by  a  rough  colorimetric  test).  Place  the 
metal  in  a  wide,  covered  beaker,  and  add  20  c.c.  of  strong 
hydrochloric  acid  ;  heat  till  all  action  is  at  an  end  ;  rinse 
the  cover  and  sides  of  the  beaker  from  splashings,  and  eva- 
porate the  solution  gently  to  complete  dryness.  If  the 
evaporation  has  not  been  too  rapid,  the  chlorides  may  be 
almost  entirely  detached  from  the  bottom  of  the  beaker  in 
a  brittle  cake.  This  is  broken  up  into  small  pieces  by  means 
of  a  platinum  spatula,  and  as  much  as  possible  is  brushed 
out  into  a  clean  dry  porcelain  dish.  A  small  quantity  of 
the  chlorides  will,  however,  remain  adhering  to  the  beaker  ; 
this  may  be  lemoved  with  2  or  3  c.c.  of  dilute  hydro- 
chloric acid.  The  solution  is  poured  into  a  deep  platinum 
crucible,  the  beaker  rinsed  with  1  or  2  c.c.  of  water,  the 
washings  added  to  the  crucible,  the  contents  of  which  are 
now  evaporated  to  dryness  on  a  sand-bath.  When  dry 
the  main  quantity  of  the  chlorides  is  carefully  brushed  out 
of  the  porcelain  into  the  platinum  dish,  and  is  reduced  to 
a  fine  powder  by  means  of  a  little  pestle  made  from  glass 
rod.  The  spatula  and  pestle  are  cleaned  into  the  crucible. 
The  finely-divided  chlorides  are  now  thoroughly  mixed 
with  an  excess  of  fusion  mixture  (1  part  dry  sodium  car- 
bonate to  1  part  powdered  nitre),  a  cover  is  placed  over 
the  crucible,  and  its  contents  are  fused  over  a  gas  blow- 
pipe till  quite  liquid.  By  this  treatment  the  iron  is  con- 
verted into  insoluble  oxide,  the  manganese,  silica,  and 
chromium  respectively  into  alkaline  manganate,  silicate, 
and  chromate.  When  cool  the  crucible  is  placed  in  a 
beaker  containing  80  c.c.  of  boiling  water,  and  is  gently 


746  THE    ASSAY   OF   CHROMIUM. 

boiled  till  the  fused  mass  is  detached  and  dissolved  out. 
This  may  be  assisted  by  occasional  stirring  with  a  glass 
rod.  When  clear  from  oxide,  remove  the  crucible  and 
cover,  washing  them  well  with  hot  water.  Add  3  or  4 
drops  of  alcohol  to  decompose  the  manganate,  and  allow 
the  iron  and  manganese  oxides  to  settle  thoroughly, 
When  the  supernatant  liquid  is  quite  clear  it  is  decanted 
on  a  close  double  filter,  the  filtrate  being  received  into  a 
clean  beaker.  The  precipitates  are  disturbed  as  little  as 
possible.  When  all  the  clear  liquid  has  passed  through,  the 
filter  is  well  washed  with  hot  water.  The  precipitates  are 
now  washed  twice  by  decantation  with  30  c.c.  of  hot  water  ; 
at  the  second  washing  the  contents  of  the  beaker  are  allowed 
to  drain  gently  into  the  filter,  which  is  now  allowed  to 
drain  thoroughly,  and  is  removed  without  further  washing. 
These  precautions  in  washing  must  be  strictly  carried  out, 
as  the  ferric  oxide  is  in  such  an  exceedingly  fine  state  of 
division  that  any  attempt  to  wash  or  disturb  it  on  the 
filter  will  inevitably  cause  some  of  it  to  pass  through  into 
the  chromium  solution.  The  clear  yellow  filtrate  contains 
chromium  and  silica,  to  it  is  added  20  c.c.  of  hydrochloric 
acid,  the  cover  being  kept  on  the  beaker,  to  prevent  the 
projection  of  the  solution  by  the  evolved  carbonic  acid. 
The  solution  is  now  well  boiled  until  all  the  carbonic  acid 
and  nitrous  fumes  are  driven  off.  Its  colour  will  now  be 
green,  owing  to  reduction  to  chloride.  Dilute  ammonia 
is  added  until  alkaline,  and  the  solution  heated  nearly  to 
boiling.  The  resulting  precipitates  consist  of  chromium 
silicate  mixed  with  alkaline  salts.  It  is  collected  on  a 
filter  (previously  well  washed  with  hot  dilute  hydrochloric 
acid  to  free  it  from  iron),  and  is  slightly  washed.  When 
the  washings  have  drained  through,  the  precipitate  is  dis- 
solved off  the  filter  with  hot  dilute  hydrochloric  acid,  the 
filtrate  being  received  into  the  beaker  in  which  the  precipi- 
tation took  place.  The  solution  is  now  evaporated  to  dry- 
ness  to  render  the  silica  insoluble.  The  soluble  is  taken 
up  with  10  c.c.  hydrochloric  acid  and  90  c.c.  of  water, 
and  is  filtered  through  a  washed  filter  into  a  clean  beaker, 
the  filter  being  well  washed.  The  precipitation  is  now 


VOLUMETRIC   ESTIMATION   OF   CHROMIUM.  747 

repeated  as  above,  and  the  chromic  hydrate  comes  down 
free  from  silica  and  alkaline  salts.  It  is  collected,  washed, 
dried,  ignited,  and  weighed  as  chromic  oxide. 

Precautions. — Only  three  or  four  drops  of  alcohol 
should  be  added,  as  this  quantity  is  sufficient,  not  only  to 
precipitate  the  manganese,  but  also  to  effect  the  reduction 
to  chloride.  If  too  much  is  added  organic  compounds  are 
formed,  which  tend  to  prevent  the  complete  precipitation 
of  the  hydrate.  The  ammonia  in  the  last  precipitation 
should  be  added  in  the  least  possible  excess,  and  the  solu- 
tion should  be  heated  gently  nearly  to  boiling.  If  any 
great  excess  of  ammonia  be  present,  and  if  the  solution  is 
boiled,  the  glass  of  the  beaker  is  attacked  and  the  result  is 
high.  The  method,  if  properly  carried  out,  is  accurate. 

Mr.  W.  J.  Sell  has  devised  the  following  method  for 
the  volumetric  estimation  of  chromium.  The  solution, 
containing  chromium  acidified  with  sulphuric  acid,  is 
boiled,  and  a  dilute  solution  of  permanganate  added  to  the 
boiling  liquid  until  a  purplish  tint  remains  after  boiling  for 
three  minutes.  The  solution  is  then  rendered  slightly 
alkaline  with  sodium  carbonate,  alcohol  is  added,  and  the 
manganese  filtered  off.  The  chromic  acid  in  the  filtrate  is 
estimated  by  titration  with  iodine  and  sodium  hyposul- 
phate.  The  author  has  successfully  applied  the  method 
to  the  estimation  of  chromium  in  chromic  iron  ore.  He  re- 
commends the  following  plan  of  effecting  its  decomposition. 
The  chromic  iron  ore  is  placed  on  the  top  of  about  ten  times 
its  weight  of  a  mixture,  composed  of  one  molecule  of  well- 
fused  and  powdered  sodium  bisulphate  to  two  molecules  of 
sodium  fluoride,  and  the  whole  is  ignited  for  fifteen  minutes. 
An  amount  of  sodium  bisulphate  is  now  added  equal  to 
that  of  the  mixture  taken,  and  when  thoroughly  fused  a 
further  addition  of  an  equal  quantity  of  bisulphate  is 
made,  the  mass  fused,  and  then  rapidly  cooled.  The  fused 
mass  so  obtained  dissolves  completely  in  boiling  water 
acidified  with  sulphuric  acid.  In  this  way  a  determination 
can  be  made  in  an  hour  and  a  quarter. 

Dr.  S.  Kayser  ('  Zeitschrift  ftir  Analy tische  Chemie, ' 
1876,  p.  187)  mixes  one  part  of  the  finely-powdered  ore, 


748  THE   ASSAY   OF   CHROMIUM. 

preferably  elutriated  with  two  parts  pure  soda- ash  and 
three  parts  hydrate  of  lime,  the  latter  ingredient  pre- 
pared by  treating  calcined  marble  with  water  till  it  falls 
to  powder.  The  mixture  is  heated  to  bright  redness  for 
an  hour  in  an  open  crucible,  stirring  frequently. 


749 


CHAPTEE  XXI. 

THE   ASSAY   OF   ARSENIC. 


THE  minerals  from  which    arsenic   is    produced   are  the 
following  : — 

Native  arsenic. 

Arsenical  pyrites,  FeS2  +  FeAs,  containing  46-6  As  and  19'6  S. 

Arsenical  pyrites,  Fe4As3,  containing  66'8  As. 

Speiskobalt  (Co,NiFe),  As. 

Glanzkobalt,  CoS2  +  CoAs. 

Coppernickel,  Ni^As. 

Nickel  and  cobalt  arsenical  pyrites  (Co,Ni,Fe)S2  +  (Co,Xi,Fe),As. 

White  arsenical  nickel,  Ni As  ;  Tennantite  (Ou2S,SeS)4,AsS3. 

Kealgar,  AsS2  and  yellow  arsenic  AsS3. 

Assay  for  Arsenic. — 50  grains  of  the  finely  pulverised 
mineral  are  deflagrated  with  200  of  potassium  nitrate  and 
200  of  sodium  carbonate  in  a  porcelain  crucible.  When 
the  crucible  is  cold,  it  and  its  contents  are  to  be  treated 
with  water,  as  in  the  case  of  chromium.  The  solution  will 
contain  potassium  arseniate,  and  (if  the  ore  had  in  its  con- 
stitution sulphur,  which  is  most  likely)  potassium  sulphate. 
Lead  nitrate  must  be  added  to  the  solution  (made  neutral 
with  nitric  acid,  if  requisite)  :  a  mixture  of  lead  arseniate 
and  sulphate  is  precipitated  ;  this  precipitate  is  well  washed 
on  a  filter,  and  digested  with  dilute  nitric  acid  ;  this  agent 
dissolves  out  the  lead  arseniate,  and  leaves  the  sulphate. 
Filter,  and  saturate  the  filtered  solution  with  soda,  which 
will  throw  down  the  arseniate  ;  this  must  be  collected  on 
a  filter,  washed,  dried,  and  weighed.  Every  100  parts  cor- 
respond to  22 -2  of  metallic  arsenic,  or  29  parts  of  arsenioua 
acid  (the  common  white  arsenic  of  commerce). 

This  method  is  only  approximative :  the  following  is- 
the  better  plan  : — 

Digest  the  ore  in  strong  nitric  acid  until  nothing  more  is 


750  THE   ASSAY   OF   ARSENIC. 

taken  up  (the  action  may  be  facilitated  by  the  occasional 
addition  of  a  crystal  or  two  of  potassium  chlorate),  and  all 
action  on  the  addition  of  fresh  acid  is  at  an  end  :  dilute 
with  water,  and  filter :  to  the  filtered  solution  add  lead 
nitrate,  and  proceed  as  above. 

For  estimating  the  amount  of  arsenic  in  ores,  Mr. 
Parnell  says  that  the  neatest,  simplest,  and  most  accurate 
mode  of  procedure  is  to  heat  the  finely-divided  sample  in 
a  gentle  stream  of  chlorine  gas  to  a  temperature  of  about 
200°  C.,  and  to  collect  the  escaping  arsenic  chloride  in 
chlorine -water.  If  free  from  antimony,  the  liquid  may  be 
well  boiled,  to  expel  free  chlorine,  and  the  arsenic  preci- 
pitated with  sulphuretted  hydrogen,  and  weighed  as  penta- 
sulphide. 

In  cases  where  the  arsenic  is  obtained  in  the  form  of 
arsenio-magnesian  phosphate  (as  in  separation  of  the  metal 
from  antimony  or  copper),  the  most  accurate  plan  would 
be  to  dissolve  the  precipitate  in  hydrochloric  acid,  and  pre- 
cipitate the  arsenic  as  peritasulphide.  When  the  amount 
of  arsenic  is  small,  it  may  be  weighed  as  the  double  arse- 
niate.  The  sample  should  not,  however,  be  dried  at  a  higher 
temperature  than  that  of  an  ordinary  water-bath — namely, 
about  95°  C.  Perfectly  accurate  results  could,  no  doubt, 
be  obtained  by  drying  the  precipitate  over  sulphuric  acid, 
when  it  retains  its  six  equivalents  of  water.  The  only 
objection  is  that  it  would  take  many  days  for  a  filter  con- 
taining a  precipitate  to  be  properly  dried  by  this  means. 


751 


CHAPTER  XXII. 

THE   ASSAY   OF   MANGANESE. 

THE  following  are  the  commercially  valuable  minerals  con- 
taining manganese. 

Pyrolusite,        Mn02,  containing  1 8'0  p.c.  of  available  oxygen. 
Braunite,          Mn2O3,  „  10-0  „  „ 

Manganite,       Mn203,  „  9-0  „  „ 

Varvicite,         Mn202  +  Mn203,HO,          „  13-8  „  „ 

Hausmannite,  MnO  +  Mn203,  „  6'8  „  •        „ 

Psilomelane,    Mn2Os. 

The  assay  of  this  metal  is  confined  to  the  amount  of 
peroxide  any  one  of  its  ores  may  contain.  There  are 
several  methods  of  effecting  this,  and  the  best  of  these  will 
be  described  below. 

Valuation  of  Manganese  Ores. — The  best  methods  used 
for  the  valuation  of  manganese  ores  are  not  necessarily 
those  which  give  in  the  most  rapid  and  accurate  manner 
the  absolute  amount  of  manganese  peroxide  present  in  the 
ore.  The  analyst  must  bear  in  mind  that  the  commercial 
value  of  manganese  ore  depends  on  its  power  of  liberating 
chlorine  from  hydrochloric  acid  ;  and  it  not  unfrequently 
happens  that  an  ore,  which  on  accurate  analysis  would  be 
reported  to  contain  a  high  percentage  of  manganese  per- 
oxide, likewise  contains  some  other  mineral  (iron  protoxide 
or  magnetic  oxide),  which  will  materially  reduce  the  value 
of  the  manganese  as  a  chlorine-yielding  ore.  It  is  on  this 
account  that  some  processes — excellent  though  they  be 
from  a  purely  analytical  point  of  view — have  fallen  into 
discredit  amongst  manufacturers,  whilst  other  processes 
which  do  not  profess  to  give  the  amount  of  manganese  per- 
oxide actually  present,  but  only  that  available  for  liberating 
chlorine,  are  now  generally  adopted.  In  the  following 


752  THE   ASSAY   OF   MANGANESE. 

pages  are  given  the  methods  of  testing  manganese  ore  for 
the  available  peroxide  which  have  best  stood  the  test  of 
practical  experience. 

Messrs.  Sherer  and  Kumpf,  after  examining  all  the  most 
approved  methods  in  Dr.  Fresenius's  laboratory  at  Wies- 
baden, have  come  to  the  conclusion  that  Bunsen's  method 
is  the  best  for  rapidly  giving  the  amount  of  available  man- 
ganese in  an  ore.  This  process  is  carried  out  by  dissolving  a 
weighed  quantity  of  the  sample  in  strong  hydrochloric  acid 
in  a  small  flask,  until  complete  decomposition  has  taken 
place.  The  escaping  chlorine  is  received  in  a  strong  solution 
of  potassium  iodide,  and  the  liberated  iodine  subsequently 
estimated  by  means  of  a  standard  solution  of  sodium  hypo- 
sulphite and  a  solution  of  starch.  To  prevent  the  solution 
of  potassium  iodide  from  being  sucked  back  into  the  gene- 
rating flask,  a  few  small  pieces  of  magnesiteare  introduced 
with  the  manganese,  so  that  a  continual  slight  escape  of 
carbonic  acid  takes  place  through  the  solution.  The  solu- 
tion of  sodium  hyposulphite  is  tested  by  means  of  carefully 
prepared  pure  iodine,  dissolved  in  potassium  iodide.  The 
solution  should  be  of  such  a  strength  that  1000  c.c.  of 
sodium  hyposulphite  solution  corresponds  to  from  2  to  3 
grins,  of  manganese  peroxide.  In  this  estimation  the 
iodine  liberated  by  the  chlorine  should  be  tested  as  soon 
as  possible  after  the  decomposition  ;  it  gives  higher  results 
after  standing  24  hours  than  before.  These  higher  results 
are  caused  by  the  liberation  of  iodine  by  spontaneous 
decomposition  of  hydriodic  acid,  set  free  by  the  hydro- 
chloric acid,  distilled  over  during  the  process.  The  follow- 
ing experiment  proves  this : — A  few  drops  of  hydrochloric 
acid  were  added  to  a  solution  of  potassium  iodide.  The  solu- 
tion remained  for  some  hours  colourless,  but,  after  standing 
twenty-four  hours,  had  become  quite  yellow,  and  was  found 
to  contain  free  iodine  sufficient  to  indicate  8  per  cent,  of 
manganese  peroxide  when  titrated  with  hyposulphite. 

Messrs.  Sherer  and  Eumpf  have  made  the  suggestion 
that  the  value  of  manganese  ores  should  be  measured  by 
chlorometrical  degrees  rather  than  by  the  actual  percentage 
of  binoxide ;  thus  tending  in  the  same  direction  as .  the 


VALUATION    OF   MANGANESE   ORES.  753 

resolution  *  passed  by  the  Association  of  Alkali  Manu- 
facturers in  1869,  in  reference  to  this  subject — a  decision 
which  would  seem  also  to  indicate  a  desire  on  the  part  of 
manufacturers  that  tests  of  manganese  ore  should  express 
the  amount  of  peroxide  available  for  liberating  chlorine, 
and  not  the  amount  actually  present  in  the  ores. 

For  the  above  reasons,  Dr.  Paul  adopts  Mohr's  method 
of  using  a  known  quantity  of  a  standard  solution  of  oxalic 
acid,  together  with  excess  of  sulphuric  acid,  for  dissolving 
the  ore ;  if  necessary,  boiling  until  the  ore  is  completely 
dissolved,  and  then,  by  means  of  a  standard  solution  of 
permanganate,  determining  the  quantity  of  oxalic  acid 
remaining  undecom posed.  This  method  is  very  conve- 
nient for  testing  manganese  ores,  and  involves  only  one 
weighing  for  each  test.  The  results  obtained  are  also 
very  uniform. 

This  method  has  also  the  advantage  of  giving  results 
which  fairly  represent  the  amount  of  available  peroxide 
in  manganese  ores  ;  for  any  iron  that  may  be  present  as 
metal  or  protoxide  would  consume  an  equivalent  quantity 
of  permanganate  solution,  and  thus  apparently  reduce  the 
quantity  of  oxalic  acid  decomposed  by  the  peroxide  to  an 
extent  proportionate  to  the  amount  of  iron  existing  in  the 
ore.  Thus,  for  instance,  if  the  quantity  of  oxalic  acid 
decomposed  by  100  grains  of  manganese  ore  free  from 
iron  or  ferrous  oxide  were  109* 53  grains,  the  ore  would 
contain  76-5  per  cent,  of  peroxide,  and  the  whole  of  that 
would  be  available.  But,  if  the  100  grains  of  ore  also 
contained  5- 6  grains  of  metallic  iron,  or  an  equivalent  of 
protoxide,  the  permanganate  solution  required  for  per- 
oxidising  that  iron  would  represent  6*3  grains  of  oxalic 
acid,  and  the  quantity  of  oxalic  acid  decomposed  by  the 
peroxide  would  appear  so  much  less  than  it  really  was,  or 
103-23  grains  instead  of  109-53  grains.  Accordingly,  the 
amount  of  peroxide  would  be  represented  as  72*1  per 
cent,  instead  of  76'5  per  cent. :  and  that  would,  in  fact, 

*  ( That,  as  the  testing  of  manganese  according  to  the  method  of  Will  and 
Fresenius,  is,  in  the  opinion  of  the  meeting,  incorrect,  and  yields  uncertain  results, 
it  is  recommended  to  members  of  this  Association  not  to  buy  by  that  test.' 

3  c 


754  THE   ASSAY   OF   MANGANESE*     < 

be  the  amount  of  peroxide  available  for  generating  chlo- 
rine. 

This  method  of  testing  recommends  itself  by  its  sim- 
plicity, and  by  the  fact  that  the  standard  solutions  of 
oxalic  acid  and  permanganate  will  keep  for  a  long  time 
without  alteration  of  value.  The  oxalic  acid  solution 
contains  63  grms.  in  the  litre,  and  1  c.c.  is  equivalent  to  5 
c.c.  of  the  permanganate  solution. 

Mr.  John  Pattinson  prefers  a  modification  of  Otto's 
process  for  the  valuation  of  manganese,  which  consists  in 
boiling  the  ore  with  a  known  weight  of  a  proto-salt  of  iron, 
arid  then  estimating  the  excess  of  iron  by  a  standard 
solution  of  potassium  bichromate.  This  modified  process, 
in  his  opinion,  requires  less  skill  and  care  at  the  hands  of 
the  operator  than  Bunsen's  method,  as  described  by 
Messrs.  Scherer  and  Eumpf.  30  grs.  of  clean  iron  wire 
are  placed  in  a  20-oz.  flask,  along  with  3  ozs.  of  dilute 
sulphuric  acid,  made  by  adding  3  parts  of  water  to  1  of 
oil  of  vitriol.  A  cork,  through  which  passes  a  tube  bent 
twice  at  right  angles,  is  inserted  in  the  neck  of  the  flask, 
and  the  flask  is  heated  over  a  gas  flame  until  the  iron  is 
dissolved.  The  bent  tube  is  placed  so  as  to  dip  into  a 
small  flask  or  beaker  containing  a  little  water.  When  the 
iron  is  quite  dissolved,  30  grs.  of  the  finely-pounded  and 
dried  sample  of  manganese  ore  to  be  tested  are  put  into 
the  flask,  the  cork  replaced,  and  the  contents  again  made 
to  boil  gently  over  a  gas  flame  until  it  is  seen  that  the 
whole  of  the  black  part  of  the  manganese  is  dissolved. 
The  water  in  the  small  flask  or  beaker  is  then  allowed  to 
recede  through  the  bent  tube  into  the  larger  flask,  more 
distilled  water  is  added  to  rinse  out  the  small  flask  or 
beaker  and  bent  tube,  the  cork  well  rinsed,  and  the  con- 
tents of  the  flask  made  up  to  about  8  or  10  ozs.  with  dis- 
tilled water.  The  amount  of  iron  remaining  unoxidised 
'in  the  solution  is  then  ascertained  by  means  of  a  standard 
solution  of  potassium  bichromate.  The  amount  the  bi- 
chromate indicates,  deducted  from  the  total  amount  of 
iron  used,  gives  the  amount  of  iron  which  has  been 
peroxidised  by  the  manganese  ore,  and  from  this  can  be 


VALUATION   OF   MANGANESE    ORES.  755 

calculated  the  percentage  of  manganese  peroxide  contained 
in  the  ore.  Thus,  supposing  it  were  found  that  4  grs.  of 
iron  remained  unoxidised,  then  30  —  4  =  26  grs.  of  iron, 
which  have  been  oxidised  by  the  30  grs.  of  ore.  By  a 
simple  calculation  it  is  found  that  this  26  grs.  of  iron  are 
equivalent  to  20'43  grs.  of  manganese  peroxide,  the 
amount  of  peroxide  in  the  30  grs.  of  ore.  The  percent- 
age is,  therefore,  68'10. 

It  must  be  understood  that  if  an  ore  contains  a  mix- 
ture of  one  atom  of  manganic  oxide,  and  two  atoms  of 
magnetic  iron  oxide,  or  27*3  per  cent,  of  the  former,  with 
7 2- 7  per  cent,  of  the  latter  ;  in  such  a  mixture  the  method 
of  Fresenius  and  Will  will  indicate  with  precision  the 
amount  of  manganese  peroxide,  but  on  adding  hydrochloric 
acid  to  this  mixture  not  a  trace  of  chlorine  will  be  given 
off,  since  the  free  atom  of  oxygen  of  the  manganese 
peroxide  is  just  sufficient  for  the  oxidation  of  the  2  atoms 
of  iron  protoxide  of  the  magnetic  iron  ore  ;  in  the  same 
way  a  mixture  of  manganese  binoxide  with  iron  protosul- 
phate  or  protocarbonate  of  that  metal  will  be  perfectly 
worthless  as  an  article  for  chlorine-making  use. 

Dr.  Mohr  accordingly  recommends  that  manganese 
ores  and  samples  of  manganese  peroxide  should  be 
always  tested,  previous  to  analysis,  with  an  astatic  mag- 
netic needle,  and  he  further  recommends  Dr.  Bunsen's 
process  (given  on  p.  752)  as  the  best  and  surest  method 
of  analysis.  This  process  is  really  the  same  as  that  which 
the  manufacturer  employs  for  making  chlorine ;  any 
magnetic  iron  ore  present  will  become  oxidised  in  both 
processes,  and  a  special  examination  for  magnetic  iron 
oxide  is  rendered  unnecessary,  while  the  available  manga- 
nese for  the  production  of  chlorine  only  is  estimated. 

Mr.  J.  Pattinson  proposes  the  following  method  of 
precipitating  manganese  entirely  as  peroxide,  and  applies 
it  to  the  volumetric  determination  of  manganese.  He 
finds  that  the  whole  of  the  manganese  in  a  solution  of 
manganous  chloride  can  be  precipitated  as  peroxide,  if  a 
certain  amount  of  ferric  chloride  be  present,  by  a  suf- 
ficient excess  of  a  solution  of  chloride  of  lime  or  bromine 

3  c  2 


756  THE   ASSAY   OF   MANGANESE. 

water,  adding,  after  heating  the  solution  to  from  140°  to 
160°  F.,  an  excess  of  calcium  carbonate,  and  then  well 
stirring  the  mixture.  Zinc  chloride  may  be  substituted 
for  ferric  chloride.  The  author  recommends  the  follow- 
ing solutions,  etc.  The  clear  liquid  obtained  by  decanta- 
tion  from  a  1'5  per  cent,  solution  of  bleaching-powder, 
light  granular  calcium  carbonate  obtained  by  precipitating 
an  excess  of  calcium  chloride  by  sodium  carbonate  at 
180°  P.,  a  1  per  cent,  solution  of  ferrous  sulphate  in 
dilute  (1  in  4)  sulphuric  acid,  standard  solution  of  potas- 
sium dichromate  equivalent  to  1  part  of  iron  in  100  of 
solution.  The  application  of  the  process  to  manganiferous 
iron  ores  is  as  follows : — 10  grains  of  the  ore,  dried  at 
212°,  are  dissolved  in  a  20  oz.  beaker  in  about  100  fluid 
grains  of  hydrochloric  acid  (sp.  gr.  1*18).  Calcium 
carbonate  is  then  added,  until  the  free  acid  is  neutralised 
and  the  liquid  turns  slightly  reddish.  6  or  7  drops  of 
hydrochloric  acid  are  now  added,  and  1000  grains  of 
the  bleaching-powder  solution,  or  500  grains  of  saturated 
bromine  water,  and  boiling  water  run  in  until  the  tempe- 
rature is  raised  from  140°  to  160°  F. ;  25  grains  of  calcium 
carbonate  are  added,  and  the  whole  well  stirred.  If  the 
supernatant  solution  has  a  pink  colour,  the  permanganate 
is  reduced  by  a  few  drops  of  alcohol.  The  precipitated 
oxides  of  iron  and  manganese  are  filtered  off  and  washed. 
1000  grains  of  the  acidified  ferrous  sulphate  solution  are 
carefully  measured  into  the  20-oz.  beaker  already  used  ; 
the  filter,  with  its  washed  contents,  added.  A  certain  quan- 
tity of  the  ferrous  sulphate  is  oxidised  by  the  manganese 
binoxide,  this  quantity  is  estimated  with  the  standard 
dichromate  solution,  when  the  quantity  of  manganese  bin- 
oxide  can  easily  be  calculated.  The  iron  present  must  be 
at  least  equal  in  weight  to  the  manganese  during  the  pre- 
cipitation, in  order  to  ensure  the  absence  of  lower  oxides. 


757 


CHAPTEE  XXni. 

THE   ASSAY   OF   NICKEL   AND   COBALT 

ORES  OF  NICKEL. 

Nickel  oxide. 

Nickel  sulphide 

Nickel  arsenide ;  kupfernickel. 

Nickel  ars«»nio-sulphide  ;  grey  nickel. 

Nickel  antimonio-sulphide. 

Nickel  arseniate. 

Nickel  arsenite. 

Nickel  silicate. 

ORES  OP  COBALT. 

Cobalt  oxide. 

•          Cobalt  sulphide  ;  cobaltine. 
Cobalt  sulphate. 
The  cobalt  arsenides. 
Arsenio-sulphide,  or  grey  cobalt. 
Cobalt  arsenite. 

THE  analysis  of  cobalt  ores  is  the  most  tedious,  with  the 
exception  of  those  of  platinum,  of  any  that  fall  under  the 
assayer's  notice — the  greatest  difficulty  being  in  the  sepa- 
ration of  cobalt  and  nickel.  The  following  is  Mr.  Hadow's 
process : — 

The  only  examination  which  the  ore  need  undergo 
previously  to  the  solution  of  a  weighed  quantity  is  with  the 
view  of  obtaining  a  rough  idea  as  to  the  amount  of  arsenic 
and  cobalt  or  nickel  present  in  the  sample ;  for  this  purpose 
a  little  may  be  roasted  on  charcoal,  or  ignited  in  a  tube, 
to  see  whether  arsenic  readily  sublimes  ;  another  portion, 
of  a  few  grains  weight,  may  be  dissolved  in  aqua  regia  in  a 
test-tube,  when  the  depth  of  the  blue  or  green  colour  will 
serve  as  an  indication  of  the  degree  of  richness  of  the  ore 
in  cobalt  and  nickel. 

If  the  ore  is  rich,  from  20  to  30  grains ;  if  poor,  from 


758  THE   ASSAY   OF   NICKEL   AND    COBALT. 

50  to  100  grains,  in  a  state  of  fine  division,  are  weighed 
out  for  the  analysis.  If  much  arsenic  has  been  found,  the 
portion,  after  weighing,  had  better  be  ignited  in  a  small 
porcelain  capsule  or  crucible  over  a  gauze  burner,  when  it 
generally  ignites  and  smoulders  away,  evolving  abundance 
of  arsenious  acid.  The  powder  ready  for  solution  is  trans- 
ferred to  a  small  4-oz.  flask  by  means  of  glazed  letter-paper 
and  a  camel's-hair  paint-brush  to  sweep  in  the  last  par- 
ticles ;  the  mouth  of  the  flask  is  then  partially  closed  by  a 
small  funnel  placed  to  catch  the  drops  projected  during 
solution.  The  ore  is  .then  drenched  with  hydrochloric 
acid,  nitric  acid  being  added  from  time  to  time,  until  all 
heavy  metallic-looking  particles  are  found  to  have  disap- 
peared from  the  bottom  of  the  flask.  The  solution  may 
then  be  decanted  from  the  insoluble  matters  into  a  half- 
pint  beaker,  together  with  the  washings  of  the  flask  ;  and 
as  sulphur  frequently  remains,  entangling  portions  of  undis- 
solved ore,  it  is  advisable  to  transfer  the  undissolved  residue 
from  the  flask  into  a  capsule,  drying  and  igniting  the  con- 
tents of  the  latter,  and  then  digesting  again  the  ignited 
matters  in  a  little  more  aqua  r-egia  ;  the  whole  of  the  latter, 
both  dissolved  and  undissolved,  may  now  be  added  to  the 
first  portion  in  the  half-pint  beaker. 

To  separate  out  iron,  arsenic,  phosphoric  acid,  and 
aluminium  from  the  solution,  sodium  acetate  may  be  added 
at  once,  and  the  liquid  boiled  ;  a  far  better  mode,  however, 
is  to  effect  a  partial  separation  of  these  ingredients  by  the 
addition  of  calcium  carbonate  in  excess  to  the  solution  of 
the  ore,  and  after  filtering  out  the  solution  containing  the 
greater  portion  of  the  cobalt  and  nickel,  and  partly  wash- 
ing the  precipitate,  to  extract  the  last  traces  of  cobalt  and 
nickel  from  the  latter  by  dissolving  it  in  hydrochloric  acid, 
adding  excess  of  sodium  acetate  and  boiling.  The  first 
filtrate  from  the  precipitate  by  calcium  carbonate  had 
better  be  collected  apart  from  the  second  filtrate  from  the 
precipitate  produced  by  sodium  acetate,  and  received  in  a 
beaker  capable  of  holding  at  least  a  quart.  The  solution 
of  the  precipitate  by  calcium  carbonate  is  best  effected  in 
a  beaker,  after  the  removal  of  the  precipitate  from  the 


-       COBALT   AND   NICKEL   ORES.  75S 

filter ;  this  is  easily  effected  by  inclining  the  funnel  Over 
the  beaker  and  sending  a  stream  of  water  from  the  wash- 
bottle  between  the  filter  and  the  upper  edge  of  the  mass 
of  precipitate,  when  the  latter  will  soon  become  detached 
and  slide  off  into  the  beaker  below  :  it  is  here  treated  with 
dilute  hydrochloric  acid,  to  dissolve  all  but  the  insoluble 
residues  of  the  ore  which  had  not  been  previously  filtered 
off,  and  then  a  solution  of  sodium  acetate  is  added  in 
excess  (indicated  by  the  deep  red  colour  of  liquid)  and  the 
whole,  heated  to  boiling,  may  be  filtered  at  once.  Iron 
thus  separated  out,  in  presence  of  free  acetic  acid,  has  less 
tendency  to  retain  cobalt  than  when  precipitated  by  means 
of  calcium  carbonate,  besides  which  the  cobalt  and  nickel 
in  the  filtrate  are  left  in  the  condition  of  acetates,  a 
necessary  step  preparatory  to  their  separation  from  man- 
ganese, &c. 

This  method  of  separating  out  iron,  &c.,  though  very 
effectual,  was  often  at  first  found  to  be  attended  with  diffi- 
culties, for  if  much  arsenic  were  not  present  the  basic  iron 
acetate  frequently  became  slimy  towards  the  end  of  the 
filtration,  only  allowing  the  boiling  washing  water  to  pass 
with  such  extreme  slowness  as  to  render  the  method  almost 
useless,  until  it  was  found  that  the  addition  of  a  little 
sodium  sulphate  during  the  washing  at  once  and  perma- 
nently effected  a  cure,  causing  filtration  to  proceed  rapidly, 
and  diminishing  the  tendency  of  the  iron  to  pass  the  filter ; 
another  difficulty  was,  that  when  sodium  acetate  was  added 
at  once  to  the  original  solution  of  the  ore,  the  solution, 
often  containing  much  cobalt  and  nickel  as  acetates,  and 
filtered  in  a  concentrated  state,  yielded  to  the  filter  paper 
sufficient  cobalt  and  nickel  to  occasion  distinct  loss  ;  this 
was  avoided  by  separating  out  the  great  bulk  of  the  cobalt 
and  nickel  in  solution  as  chlorides  by  means  of  calcium 
carbonate,  as  above  recommended,  and  then  the  weaker 
solution,  being  comparatively  strongly  acid,  could  be 
filtered  without  loss.  This  second  filtrate  may  still  retain 
traces  of  iron  ;  a  little  sodium  acetate  may  be  added  to 
make  sure  that  none  remains  in  the  condition  of  chloride, 
which  would  be  indicated  at  once  by  a  reddening  of  the 


760         THE  ASSAY  OF  NICKEL  AND  COBALT. 

liquid,  and  the  whole  is  then  boiled  thoroughly  once  more; 
if  rendered  at  all  turbid  passed  through  a  filter  again,  then 
nearly  neutralised  with  ammonia,  and  finally  added  to  the 
bulk  of  the  cobalt  and  nickel  solution  in  the  quart  beaker. 
There  will  in  all  probability  be  enough  of  the  sodium  and 
ammonium  acetates  present  to  convert  the  entire  quantity 
of  cobalt  and  nickel  into  acetates  without  further  addition, 
and  rendering  it  thus  ready  for  the  next  operation. 

If  sulphuretted  hydrogen  be  now  transmitted  through 
the  solution  containing  cobalt  and  nickel,  these  metals  are 
perfectly  and  completely  separated  without  a  trace  of 
manganese,  magnesium,  calcium,  aluminium,  or  soluble 
silica,  which,  when  present,  invariably  accompany  the  sul- 
phides precipitated  by  ammonium  sulphide ;  the  sulphides, 
moreover,  thus  precipitated  from  an  acetic  solution,  have 
much  less  tendency  to  oxidise  while  on  the  filter,  so  that 
their  washing  may  be  more  perfectly  accomplished  than 
in  the  former  case.  The  passage  of  sulphuretted  hydrogen 
may  be  conveniently  effected  at  the  end  of  the  day,  and 
the  next  morning  the  sulphides  will  be  found  perfectly 
settled  at  the  bottom  of  the  beaker,  permitting  the  great 
bulk  of  the  liquid  (tested  first  to  make  sure  of  the  removal 
of  cobalt  and  nickel)  to  be  drawn  off  and  thrown  away,  or 
at  least  rapidly  run  through  a  filter  ;  the  sulphides  collected 
at  the  bottom,  together  with  that  which  always  adheres  to 
the  sides  of  the  beaker,  and  which  may  be  detached  with- 
out loss  by  a  caoutchouc-covered  glass  rod,  are  then  well 
washed  on  the  filter  with  boiling  water  until  all  soluble 
matters  are  perfectly  removed.  The  sulphides,  perfectly 
washed,  are  now  to  be  dried  by  placing  the  funnel  with 
the  filter  in  a  broken  beaker  on  wire  gauze,  at  a  safe 
distance  over  a  lamp,  and  when  dry  they  may  be  detached 
from  the  filter  into  a  small  beaker  of  from  1  to  2  oz.  capa- 
city, capable  of  being  covered  with  a  watch-glass ;  the 
filter  itself  is  ignited,  and  the  well-burnt  ashes  added  to 
the  sulphides,  which  are  then  to  be  cautiously  treated  with 
nitric  acid,  the  action  being  rather  violent,  and,  if  care  be 
not  taken,  liable  to  occasion  loss.  With  the  aid  of  a  little 
heat,  the  whole  should  pass  into  solution. 


ASSAY   OF   NICKEL    ORES.  761 

In  addition  to  cobalt  and  nickel  the  solution  may  still 
contain  zinc,  together  with  copper,  and  other  metals  pre- 
cipitable  by  sulphuretted  hydrogen  from  hydrochloric 
solutions  ;  by  passing  sulphuretted  hydrogen  now  through 
the  nitric  solution,  somewhat  diluted,  these  latter  are 
readily  precipitated  and  removed  by  filtration.  Zinc,  how- 
ever, may  still  remain,  to  detect  and  remove  which  it  is 
necessary  to  expel  the  sulphuretted  hydrogen  still  remain- 

Jing  in  the  solution  by  boiling,  to  add  solution  of  ammonia 
until  a  precipitate  occurs,  and  then  to  acidify  pretty  strongly 
with  acetic  acid  ;  if  sulphuretted  hydrogen  slowly  trans- 
mitted, or  fresh  sulphuretted  hydrogen  water,  occasions 
a  milkiness,  zinc  is  present,  and  the  slow  passage  of  the 
gas  is  to  be  continued  until  the  precipitate  begins  to  show 
signs  of  darkening.  The  liquid  is  then  filtered.  The  zinc 
may  be  identified  as  such  by  collecting  and  igniting  the 
precipitate,  when  a  trace  of  cobalt  carried  down  with  it 
(and  which  may  be  separated  out,  if  desired,  by  a  repetition 
of  the  process  on  the  precipitate)  will  produce  the  beautiful 
and  well-known  Rinman's  green. 

The  filtrate,  containing  only  nickel,  cobalt,  and  salts 
of  ammonia,  is  treated  with  some  pure  sulphuric  acid  and 
evaporated  to  dryness  in  a  weighed  capsule,  and  heated 
sufficiently  to  ^xpel  the  excess  of  sulphuric  acid  and  all 
the  ammoniacal  salts.  The  residual  cobalt  and  nickel  sul- 
phates may  now  be  weighed  in  a  covered  crucible.  This 
form  of  weighing  these  metals  is  easy,  exact,  and  may  be 
rapidly  executed.  The  weight  of  the  ash  of  a  filter  of  the 
size  used  for  collecting  the  sulphides  must  be  ascertained 
after  treatment  with  sulphuric  acid,  and  subsequent  ex- 
pulsion of  the  excess,  and  this  weight  deducted  from  the 
total  sulphates,  in  order  to  obtain  perfectly  correct  results. 

Assay  of  Nickel  Ores. — The  ore  of  nickel  usually  met 
with  is  the  arsenide,  containing  variable  quantities  of 
cobalt  and  iron,  and  frequently  also  copper  and  bismuth. 
It  is  finely  powdered,  mixed  with  2  parts  of  solid  caustic 
soda  and  l.j>  part  of  sulphur,  and  fused  in  an  earthen 
crucible,  gradually  increasing  the  heat  to  dull  redness, 
at  which  temperature  it  is  to  be  kept  for  some  time.  The 


762  THE   ASSAY    OF   NICKEL    AND    COBALT. 


mass  is  then  digested  in  water,  which  dissolves  the  soluble 
sodium  sulpho-arseniate,  and  leaves,  when  washed  by  de- 
cantation,  crystallised  nickel  sulphide.  Attack  this  with 
warm  hydrochloric  acid  containing  a  little  nitric  acid. 

The  solution  heated  to  about  70°  C.  is  then  submitted 
to  a  current  of  sulphuretted  hydrogen,  which  must  be 
continually  passed  until  the  liquid  is  cold.  It  is  then  to 
be  covered  over  and  left  at  rest  for  24  hours ;  the  arsenic, 
copper,  and  bismuth  come  down  as  sulphides.  These  are 
filtered  off,  and  the  filtrate  is  heated  with  potassium  chlo- 
rate or  sodium  hypochlorite  to  bring  the  iron  to  the  state 
of  sesquioxide,  which  is  then  precipitated  by  ebullition 
with  excess  of  sodium  acetate.  The  filtrate  from  the  basic 
iron  acetate  is  concentrated  by  evaporation  and  mixed 
with  a  saturated  solution  of  potassium  nitrite,*  which  will 
precipitate  all  the  cobalt. 

The  yellow  precipitate  washed  with  a  saturated  solu- 
tion of  potassium  chloride  may  be  treated  as  described 
below.  The  nickel  is  precipitated  from  the  liquid  either 
in  the  state  of  oxide  by  means  of  caustic  potash,  or  after 
concentration,  by  a  saturated  and  warm  solution  of  potas- 
sium binoxalate.  The  precipitated  oxalate  upon  calcination 
leaves  pure  nickel. 

Assay  of  Commercial  Metallic  Nickel. — Dissolve  the 
metal  in  hydrochloric  acid  containing  a  little  nitric  acid. 
Pass  sulphuretted  hydrogen  through  the  solution  until  the 
metallic  impurities  are  thrown  down,  and  then  precipitate 
the  nickel  and  cobalt  by  a  warm  saturated  solution  of 
potassium  binoxalate.  The  precipitate  after  being  washed 
and  calcined  leaves  the  nickel  (containing  a  little  cobalt) 
in  the  metallic  state. 

p:i  Assay  of  Cobalt  Ores. — Metallic  cobalt  may  be  prepared 
from  its  ores  (arsenide  or  sulphide)  by  a  similar  process  to 
that  adopted  in  the  case  of  nickel.  When  the  mineral 

*  Potassium  nitrite  is  prepared  by  fusing,  in  an  iron  crucible,  1  part  of  nitre 
with  2  parts  of  granulated  lead,  stirring  well  with  an  iron  spatula,  and  then 
heating  to  redness  until  the  lead  is  completely  oxidised.  The  fused  mass,  after 
cooling,  is  extracted  with  water,  and  the  small  amount  of  lead  which  is  dissolved 
is  precipitated  by  carefully  adding  a  mixture  of  caustic  ammonia  and  ammonium 
carbonate  or  sulphide. 


SEPARATION  OF  NICKEL  AND  COBALT.         763 

contains  more  than  70  per  cent,  of  arsenic,  a  preliminary 
fusion  should  be  performed  with  chloride  of  sodium,  to 
remove  most  of  the  arsenic.  This  may  be  continued  by 
roasting  or  by  fusion  with  a  mixture  of  sodium  carbonate 
and  sulphur. 

As  nickel  is  almost  invariably  present  in  cobalt  ores, 
this  metal  will  require  to  be  separated.  Wohler  recom- 
mends for  this  purpose  the  potassium  nitrite  process.  The 
yellow  cobalt  precipitate  is  dissolved  in  as  small  a  quantity 
of  hydrochloric  acid  as  possible,  and  sodium  acetate  is  then 
added  ;  the  addition  of  a  warm  saturated  solution  of  oxalic 
acid  now  precipitates  the  cobalt  as  oxalate.  This  oxalate 
after  being  washed  and  dried  may  be  packed  closely  in  a 
crucible  of  biscuit  porcelain,  protected  by  enclosure  in  a 
Hessian  crucible.  The  covers  being  well  luted  on,  the  whole 
is  heated  in  a  wind  furnace  or  a  forge.  If  a  sufficient  tem- 
perature has  been  obtained  the  cobalt  will  be  in  the  form 
of  a  fused  button. 

Separation  of  Nickel  and  Cobalt. — A  method  of  sepa- 
rating these  metals,  given  some  years  since  by  Liebig, 
consists  in  boiling  the  mixed  double  nickel  and  potassium 
cyanides,  cobalt  and  potassium  cyanides,  with  oxide  of 
mercury.  Nickel  oxide  is  precipitated,  while  an  equiva- 
lent quantity  of  mercury  is  dissolved  as  cyanide.  The 
method  certainly  gives  good  results,  but  is  not  free  from 
objection.  Long  boiling  is  necessary  before  the  precipi- 
tation is  complete,  and  it  is  difficult  to  prevent  bumping 
during  ebullition.  The  excess  of  mercury  oxide  must  be 
separated  from  the  nickel  oxide  by  a  special  operation, 
and  the  nickel  afterwards  again  precipitated  by  caustic 
alkali. 

According  to  Wolcott  Gibbs,*  these  inconveniences 
may  be  completely  avoided  by  employing,  instead  of  the 
oxide  alone,  a  solution  of  the  oxide  in  the  mercury 
cyanide.  When  this  solution  is  added  to  a  hot  solution 
of  the  double  cyanide  of  nickel  and  potassium,  the  whole 
of  the  nickel  is  immediately  thrown  down  as  a  pale  green 
hydrate  of  the  protoxide.  Under  the  same  circumstances 

*  '  Chemical  News/  March  17, 1865. 


764  THE   ASSAY   OF    NICKEL   AND    COBALT. 

cobalt  is  not  precipitated  from  the  double  cobalt  and  potas- 
sium cyanide.  Mr.  W.  N.  Hill,  who  has  repeatedly 
employed  this  method  and  carefully  tested  it,  has  found 
that  the  separation  effected  is  complete.  No  cobalt  can 
be  detected  in  the  precipitated  nickel  oxide  by  the  blow 
pipe,  nor  can  the  nickel  be  detected  in  the  cobalt  (finally 
separated  as  oxide)  by  Plattner's  process  with  the  gold 
bead.  The  solution  of  mercury  oxide  is  easily  obtained 
by  boiling  the  oxide  with  a  strong  solution  of  the  cyanide, 
and  filtering.  According  to  Kuhn,  the  cyanide  formed  in 
this  manner  has  the  formula  HgCy  +  3HgO.  The  hydrated 
nickel  oxide  precipitated  may  be  filtered  off,  washed,  dried, 
ignited,  and  weighed.  The  cobalt  is  more  readily  and 
conveniently  determined  by  difference,  when,  as  it  is  always 
possible,  the  two  metals  have  been  weighed  together  as 
sulphates.  We  are  not  prepared  to  say  that  this  modifi- 
cation of  Liebig's  method  of  separating  nickel  and  cobalt 
gives  better  results  than  Stromeyer's  process  by  means  of 
potassium  nitrite,  but  it  is  at  least  very  much  more  con- 
venient, and  requires  much  less  time.  The  complete  pre- 
cipitation of  cobalt  in  the  form  of  Co.203,2N03  +  3KO,N03 
usually  requires  at  least  forty-eight  hours,  and  rarely 
succeeds  perfectly  except  in  experienced  hands. 

M.  Terreil  has  proposed  a  very  excellent  method  for 
separating  these  two  metals.  The  author's  method  is 
founded — (1)  on  the  insolubility  of  roseocobaltic  hydro- 
chlorate  in  acid  liquids  and  ammoniacal  salts,  discovered 
by  M.  Fremy  ;  (2)  on  the  rapid  transformation  of  ordinary 
salts  of  cobalt  into  roseocobaltic  salts,  under  the  double 
influence  of  ammonia  and  oxidising  bodies — such  as  potas- 
sium permanganate  and  alkaline  hypochlorites  ;  (3)  on 
the  complete  precipitation  of  manganese  in  ammoniacal 
liquids  by  alkaline  hypochlorites,  and  potassium  perman- 
ganate. 

To  separate  cobalt  from  nickel,  operate  in  the  follow- 
ing manner : — 

To  the  solution  of  the  two  metals  add  an  excess  of 
ammonia,  which  re-dissolves  the  two  oxides ;  add  to  the 
hot  ammoniacal  liquid  a  solution  of  potassium  permanga- 


DETECTION   OF   NICKEL   BEFORE   THE   BLOWPIPE.  765 

nate,  sufficient  to .  cause  the  liquid  to  remain  coloured 
violet  for  a  few  instants  by  the  excess  of  permanganate. 
Boil  the  liquid  for  a  few  minutes,  then  add  a  slight  excess 
of  hydrochloric  acid,  to  re-dissolve  the  manganese  oxide 
which  will  have  formed.  Heat  the  liquid  gently  for  twenty 
or  twenty-five  minutes,  then  let  it  stand  for  about  twenty- 
four  hours.  All  the  cobalt  will  then  be  deposited  in  the 
form  of  a  beautiful  red-violet  crystalline  powder ;  the  pre- 
cipitate is  roseocobaltic  hydrochlorate,  which  collect  on  a 
weighed  filter,  wash  it  on  the  filter  with  cold  water,  then 
with  diluted  hydrochloric  acid,  or  with  a  solution  of  am- 
moniacal  salt,  and  then  with  ordinary  alcohol,  which  frees 
it  from  ammoniacal  salt.  Dry  it  at  110°,  and  weigh.  100 
parts  of  roseocobaltic  hydrochlorate  correspond  to  22-761 
of  metallic  cobalt,  or  to  28 -95 9  of  protoxide  of  cobalt. 

It  is,  however,  better  to  take  a  given  quantity  of  the 
roseocobaltic  salt,  and  reduce  it  by  dry  hydrogen ;  this 
leaves  perfectly  pure  cobalt  to  be  weighed. 

Next  boil  the  solution  containing  nickel  to  expel  the 
alcohol  which  has  been  introduced  in  washing  the  cobaltic 
salt ;  saturate  it  with  ammonia,  add  another  small  excess 
of  permanganate  of  potash,  and  boil.  All  the  manganese 
will  be  precipitated ;  filter  the  liquid,  and  all  the  nickel 
will  be  found  in  the  filtrate,  from  which  it  may  easily  be 
separated  in  the  state  of  sulphide,  and  then  transformed 
into  oxide. 

By  this  process  the  presence  of  a  ten-thousandth  part 
of  cobalt  in  a  salt  of  nickel  may  be  ascertained. 

In  this  operation  an  alkaline  hypochlorite  may  take 
the  place  of  the  potassium  permanganate,  but  then  the 
deposit  of  roseocobaltic  salt  takes  place  with  extreme 
slowness,  and  several  days  are  required  to  complete  it. 
This  reagent  is  preferable  to  permanganate  when  manga- 
nese is  to  be  separated  from  nickel  and  cobalt. 

Quantitative  Assay  of  Small  Proportions  of  Cobalt  in 
Nickel. — The  following  method  is  proposed  by  Dr.  Fleit- 
mann.  It  is  well  known  that  from  solutions  containing 
both  these  metals  the  cobalt  is  first  precipitated  by  hypo- 
chlorites,  as  a  brown  hydrate,  and  the  nickel  hydrate  does 


766  TPIE   ASSAY   OF   NICKEL   AND    COBALT. 

not  fall  until  after  a  further  addition.  The  partial  pre- 
cipitation with  sodium  hypochlorite  is  so  conducted  that 
at  least  two  parts  of  nickel  may  be  thrown  down  to  one  of 
cobalt.  The  proportion  may  be  judged  by  the  colour  of 
the  solution  of  the  precipitate.  If  this  solution  is  decidedly 
red,  more  of  the  precipitant  must  be  added.  After  a 
slight  washing  the  precipitate  is  dissolved  on  the  filter 
with  warm  hydrochloric  acid,  the  excess  of  chlorine  re- 
moved by  boiling,  and  the  mixture  of  cobaltous  and 
nickelous  oxides  is  precipitated  from  the  warm  solution 
with  potash  lye.  The  precipitate  is  filtered,  slightly  washed 
with  water,  dissolved  in  acetic  or  nitric  acid,  and  the 
cobalt  is  then  precipitated  in  the  ordinary  manner  with 
potassium  nitrite. 

Detection  of  Nickel  before  the  Blowpipe. — The  following 
is  Plattner's  method  for  detecting  nickel,  when  contained 
in  large  quantities  of  cobalt : — 

Fuse  in  the  oxidising  flame  a  moderate  quantity  of 
borax  to  a  bead  in  the  loop  of  platinum  wire,  with  suffi- 
cient oxide  of  cobalt  to  give  an  opaque  glass ;  remove  the 
assay,  and  prepare  one  or  two  similar  beads,  and  place  the 
whole  in  a  charcoal  cavity,  with  a  button  of  pure  gold 
weighing  from  fifty  to  eighty  milligrammes.  The  operator 
must  now  heat  in  the  reducing  flame,  until  he  is  satisfied 
that  the  whole  of  the  nickel  is  in  a  metallic  state  ;  the 
charcoal  during  the  action  must  be  inclined  alternately 
backwards  and  forwards,  so  that  the  gold  button  may 
flow  through  the  melted  glass,  and  form  an  alloy  with  the 
reduced  particles  of  nickel.  When  the  golden  globule 
solidifies,  it  must  be  extracted  with  a  forceps,  placed  be- 
tween paper,  and  struck  with  a  hammer,  so  as  .to  detach 
all  the  adhering  vitreous  parts.  The  auriferous  button, 
which  has  become  more  or  less  grey,  from  the  presence  of 
.nickel,  and  also  more  brittle  than  pure  gold,  is  now  to  be 
mixed  with  microcosmic  salt,  and  heated  for  some  time  in 
the  oxidising  flame.  If  the  borax-glass  has  not  been  in 
the  first  instance  oversaturated  with  oxide  of  cobalt,  a 
bead  will  now  be  obtained,  which  is  coloured  only  by 
oxide  of  nickel,  and  will  therefore  appear  brownish-red 


ASSAY/ OF   COMPLEX   NICKEL   AND    COBALT  ORES.  767 

while  hot,  and  when  cold  reddish-yellow.  Should  por- 
tions of  oxide  of  cobalt  be  also  reduced,  as  the  cobalt  is 
oxidised  before  the  nickel,  either  a  blue  glass,  coloured  by 
oxide  of  cobalt,  or  a  green  one- — if  some  nickel  was  also 
oxidised— will  be  obtained.  In  either  case  the  glass  must 
be  separated  from  the  button,  mixed  with  more  micro- 
cosmic  salt,  and  heated  in  the  oxidising  flame  until  it 
acquires  a  tinge.  If  the  borax-glass  had  not  been  over- 
saturated  at  the  commencement,  the  colour  now  obtained 
will  proceed  from  nickel,  although  the  cobalt  oxide  con- 
tains a  trace  only  ;  but  if  nickel  oxide  be  not  present,  the 
microcosmic  bead  remains  perfectly  colourless. 

In  the  assay  of  substances  containing  cobalt,  nickel, 
and  zinc,  Alex.  Olassen  ('  Zeitschrift  fur  Anal.  Chemie,' 
1879,  p.  189)  proceeds  as  follows  : — 

To  the  solution  rendered  as  neutral  as  possible,  he  adds 
so  much  neutral  potassium  oxalate  (1  part  of  the  salt  and 
3  parts  water)  that  the  precipitate  is  redissolved.  He  then 
adds,  with  stirring,  acetic  acid  about  equal  to  the  volume 
of  the  liquid.  The  precipitate  becomes  crystalline  at  a 
temperature  of  50°  to  60°  C.,  and  the  liquid  remains  clear. 
The  precipitate  is  washed  with  a  mixture  of  equal  volumes 
concentrated  acetic  acid,  alcohol,  and  water.  The  dry 
precipitates,  after  the  filter  has  been  burnt  on  a  platinum 
wire,  are  first  ignited  very  slightly  in  a  covered  platinum 
crucible,  so  that  no  particles  may  be  expelled  by  the  es- 
caping carbonic  oxide,  and  finally  are  ignited  in  an  open 
crucible. 

Ores  containing  Sulphur,  Arsenic,  Nickel,  Cobalt,  and 
Iron. —  (Arsenical  nickel-glance,  cobalt-glance,  red  and 
white  nickel  pyrites,  cobalt  speiss,  commercial  nickel.) 

In  nickel  and  cobalt-glance  sulphur  is  present  in  great 
quantity,  and  is  rarely  absent  in  the  remaining  ores.  Its 
determination  is  best  affected  in  a  separate  portion.  For 
the  separation  and  estimation  of  the  metals  the  finely- 
powdered  sample  is  oxidised  either  with  aqua  regia  or 
with  hydrochloric  acid  and  potassium  chlorate,  and  the 
arsenic  is  determined  as  directed  for  the  arsenides  and 
sulph-arsenides  of  iron. 


7C8  THB   ASSAY   OF    NICKEL    AND    COBALT. 

The  liquid  filtered  from  the  arsenic  sulphide  is  freed 
from  sulphuretted  hydrogen  by  heat,  the  iron  is  oxidised 
with  potassium  chlorate,  the  free  chlorine  expelled  by 
heat  and  the  addition  of  a  little  alcohol,  the  liquid  is 
largely  diluted,  placed  in  a  basin  and  mixed  with  sodium 
carbonate,  till  the  acid  reaction  becomes  very  faint. 
Barium  carbonate  levigated  in  water  to  a  fine  paste  is 
then  added,  till  it  lies  at  the  bottom  of  the  vessel.  After 
repeated  stirring  the  iron  is  all  precipitated.  It  is  filtered 
off,  dissolved  in  dilute  hydrochloric  acid,  sulphuric  acid 
is  added,  the  precipitate  of  barium  sulphate  removed, 
and  the  ferric  oxide  precipitated  with  ammonia.  The 
liquid  containing  the  nickel  and  cobalt  is  freed  from 
soluble  barium  compounds  by  means  of  sulphuric  acid, 
and  the  barium  sulphate  is  removed  by  filtration. 

The  filtrate,  containing  the  nickel  and  cobalt r  is  placed 
in  a  basin,  supersaturated  with  potash,  heated  to  a  boil, 
filtered,  washed  with  hot  water,  and  the  mixture  of  both 
oxides  dissolved  in  acetic  acid.  To  this  liquid  is  added  a 
concentrated  solution  of  potassium  nitrite  (if  it  contains 
free  potash  an  excess  of  acetic  acid  must  be  present),  and 
the  whole  is  let  stand  for  24  hours. 

*  A  yellow  precipitate  of  potassium  cobaltic  nitrite  is 
produced,  which  is  filtered  off  and  washed  in  the  cold  with 
a  saturated  solution  of  potassium  chloride.  More  potas- 
sium nitrite  is  added  to  the  filtrate  to  ascertain  whether 
anything  further  is  deposited.  The  yellow  precipitate  is 
digested  writh  hydrochloric  acid,  in  which  it  dissolves, 
diluted,  filtered  into  a  basin,  and  the  cobalt  oxide  is  pre- 
cipitated by  boiling  with  an  excess  of  potash.  The  pre- 
cipitate is  washed  hot,  and  when  dry  it  is  placed  in  a 
porcelain  crucible  and  strongly  ignited  in  a  current  of 
hydrogen.  After  being  allowed  to  cool  in  the  same  current, 
it  is  weighed  in  the  covered  crucible  as  metallic  cobalt.  It 
is  then  well  washed  with  water,  ignited  again  in  the  stream 
of  hydrogen,  and  finally  weighed. 

In  the  liquid  filtered  from  the  cobaltic  precipitate  the 
nickel  is  thrown  down  by  boiling  with  potash.  When 
carefully  washed,  dried,  and  ignited,  it  yields  pure  nicke] 


COPPER,   ZIXC,    AXD    NICKEL   ALLOYS.  769 

oxide,  from  the  weight  of  which  that  of  the  metal  is  cal- 
culated. 

Many  substances  of  this  class  contain  other  constituents 
in  smaller  proportion. 

Commercial  nickel  contains  silicon,  which  on  dissolving 
the  metal  in  nitric  acid,  etc.,  is  separated  out  as  silica.  For 
its  determination  the  whole  is  evaporated  to  dryness  in  the 
water-bath,  the  residue  when  cold  is  moistened  with  acid 
and  treated  with  water.  The  silica  is  then  filtered  off,  and 
the  other  constituents  are  determined  in  the  filtrate  in  the 
usual  manner. 

The  ores  of  nickel  and  cobalt  and  speiss-nickel  contain 
antimony.  It  is  precipitated  by  sulphuretted  hydrogen 
along  with  arsenic.  The  precipitate  is  dissolved  in  aqua 
regia,  and  the  two  metals  are  separated  in  the  usual 
manner. 

The  above  ores  and  furnace  products  may  also  contain 
copper,  bismuth,  and  lead.  In  presence  of  small  quantities 
of  these  metals  sulphuretted  hydrogen  should  be  passed 
through  the  solution  of  the  mixture  for  a  rather  shorter 
time  at  first.  These  are  precipitated  before  arsenic,  but  are 
accompanied  by  a  part  of  it.  The  precipitate  is  filtered  off, 
and  the  passage  of  the  sulphuretted  hydrogen  through  the 
filtrate  is  continued  till  the  arsenic  is  completely  deposited. 

The  precipitated  sulphides  whilst  still  moist  are  placed 
in  a  flask  together  with  the  filter,  and  are  digested  for  a 
considerable  time  with  concentrated  yellow  ammonium 
hydrosulphide.  When  cold  the  solution  is  diluted  and 
filtered  with  exclusion  of  air,  washed  with  water,  to  which 
a  few  drops  of  ammonium  hydrosulphide  have  been  added  ; 
the  filtrate  is  slightly  supersaturated  with  hydrochloric 
acid,  and  the  precipitate  of  arsenic  sulphide  is  filtered  off 
and  added  to  the  main  arsenical  precipitate.  The  sulphides 
(copper,  bismuth,  and  lead)  if  their  quantity  permits  are 
separated  by  methods  already  given.  If  the  quantities  of 
these  metals  are  considerable,  as  is  the  case  in  many  furnace 
products,  their  assay  is  conducted  as  pointed  out  for  lead- 
and  copper-speiss. — Rammekberg. 

Alloys  of  Copper,  Zinc,  and  Nickel. — The  assay  is  con- 

3  D 


770  THE   ASSAY   OF   NICKEL   AND   COBALT. 

ducted  as  has  been  directed  for  alloys  of  copper  and  zinc. 
The  solution  filtered  from  the  copper  sulphide,  and  con- 
taining the  zinc  and  nickel,  is  concentrated  by  evaporation 
in  order  to  remove  the  excess  of  sulphuretted  hydrogen. 
It  is  then  poured  into  a  flask,  supersaturated  with  pure 
potash  and  hydrocyanic  acid,  enough  to  dissolve  the  whole 
to  a  yellow  liquid.  From  this  solution  the  zinc  is  precipi- 
tated as  zinc  sulphide  by  means  of  potassium  monosulphide 
(prepared  by  reducing  potassium  sulphate  with  charcoal), 
and  caused  to  settle  by  digestion.  It  is  then  passed 
through  a  covered  filter,  the  filtrate  being  collected  in  a 
flask,  washed  with  cold  water,  to  which  a  little  potassium 
sulphide  has  been  added,  redissolved  by  digestion  with 
hydrochloric  acid  in  a  covered  beaker  till  the  odour  of 
sulphuretted  hydrogen  has  entirely  disappeared ;  the  di- 
luted solution  is  filtered  into  a  capsule,  and  the  zinc  oxide 
is  thrown  down  by  means  of  sodium  carbonate. 

The  filtrate  from  the  zinc  sulphide  is  boiled  in  the  flask 
with  aqua  regia  till  the  odour  both  of  sulphuretted 
hydrogen  and  hydrochloric  acid  are  expelled,  and  do  not 
return  on  the  addition  of  a  little  acid.  The  liquid  is  then 
placed  in  a  basin,  supersaturated  with  potash,  and  kept  at 
a  boil  for  a  few  minutes.  The  hydrated  nickel-oxide  is 
washed  with  hot  water,  dried,  ignited  and  weighed,  the 
proportion  of  the  metal  being  calculated  from  the  weight 
of  the  nickel-oxide. 

In  the  electrolytic  assay  of  copper  and  nickel  Herpin 
proceeds  as  follows  in  the  assay  of  alloys  of  these  metals : 
He  dissolves  1  grm.  of  the  sample  in  nitric  acid  in  a  flask 
capable  of  holding  250  c.c.,  evaporates  almost  to  dryness, 
and  adds  4-5  c.c.  sulphuric  acid,  and  water  enough  to 
make  up  a  volume  of  60-70  c.c.  The  liquid  is  rinsed  into 
a  platinum  capsule  and  submitted  to  electrolysis.  The 
copper  only  is  deposited  from  an  acid  solution. 

The  liquid,  still  containing  the  nickel,  is  poured  into  a 
flask  like  the  one  used  for  dissolving  the  alloy  ;  the  plati- 
num capsule  is  rinsed  first  with  water,  then  with  alcohol, 
dried  and  weighed  to  determine  the  copper. 

The  nickeliferous  liquid,  plus  the  washings,  is  heated  to, 


COPPER,   ZINC,   AND   NICKEL   ALLOYS.  771 

a  boil,  partially  neutralised  with  sodium  carbonate,  and 
supersaturated  with  ammonia  till  it  takes  a  blue  colour. 
It  is  then  placed  in  the  platinum  capsule,  and  submitted  to 
electrolysis.  Traces  of  lead  and  iron  do  not  interfere. 

W.  Ohl  ('  Zeitschrift  fur  Anal.  Chemie,'  1879, 523)  gives 
the  following  process  for  the  assay  of  a  nickel  speiss :  1 
grm.  finely-ground  is  placed  in  a  beaker  holding  300  c.c., 
and  covered  with  nitric  acid  or  aqua  reyia.  The  beaker  is 
covered  with  a  watch-glass  and  set  on  the  sand-bath. 
When  it  is  completely  dissolved  the  watch-glass  is  taken 
off  and  the  liquid  evaporated  to  dryness.  About  5  m.m.  of 
pure  concentrated  'hydrochloric  acid  are  added,  and  after 
the  mass  is  dissolved  the  beaker  is  half-filled  with  water. 
When  the  solution  is  hot,  sulphuretted  hydrogen  is  passed 
through  it  till  cold.  It  is  again  set  to  warm,  and  again 
treated  with  the  same  gas  till  cold.  The  precipitate  of 
copper  and  arsenic  is  quickly  deposited,  and  the  super- 
natant liquid  becomes  clear.  As  arsenic  sulphide  is  slightly 
soluble  in  water  containing  sulphuretted  hydrogen,  the 
beaker  is  set  in  a  warm  place  till  the  smell  becomes  very 
faint.  If  the  precipitate  is  a  fine  uniform  yellow  it  is 
washed  on  filtering  with  cold  pure  water  ;  if  darker,  and 
therefore  containing  more  water,  it  is  washed  with  sulphu- 
retted hydrogen  water. 

The  filtrate  containing  cobalt  and  nickel  is  evaporated 
to  dryness  in  a  capsule  holding  f  litre,  adding  a  little 
potassium  chlorate  to  oxidise  iron.  The  residue  is  taken 
up  with  a  little  hot  water  and  hydrochloric  acid,  preci- 
pitated with  pure  solution  of  soda  till  the  reaction  is 
alkaline,  redissolved  in  pure  acetic  acid,  largely  diluted 
and  heated  to  a  boil.  The  iron  is  all  deposited  as  basic 
ferric  acetate,  which  is  filtered  off  and  washed  wich  hot 
water  till --a  drop  of  ammonium  sulphide  produces  no 
turbidity  in  a  drop  of  the  washings.  The  solution,  freed 
from  the  iron,  is  evaporated  to  dryness,  dissolved  in  water, 
and  a  few  c.c.  of  dilute  sulphuric  acid,  placed  in  a  beaker 
holding  600  c.c.,  supersaturated  with  ammonia,  and  sub- 
mitted to  the  electric  current. 

When  the  electrolysis  is  complete,  a  drop  of  the  liquid 

3  D  2 


772  THE   ASSAY   OF   NICKEL   AND    COBALT. 

is  withdrawn  with  a  pipette,  filtered  and  mixed  with  a 
drop  of  ammonium  sulphide.  If  no  turbidity  is  formed  the 
platinum  cone  is  withdrawn,  washed  first  in  water,  and  then 
in  absolute  alcohol,  and  dried.  The  increase  of  weight 
gives  the  sum  of  the  cobalt  and  nickel. 


LEAD-   AND    COPPER-SPEISS. 

These  substances  are  very  complicated  products  formed 
during  the  metallurgical  treatment  of  arseniferous  and 
antimoniferous  ores  of  lead  and  copper.  They  may  con- 
tain copper,  lead,  iron,  nickel,  cobalt,  zinc,  bismuth,  silver, 
arsenic,  antimony,  and  sulphur. 

A.  Speiss  containing  little  or  no  Lead  or  Antimony. — 
One  portion  is  taken  for  the  determination  of  sulphur, 
and  another  is  dissolved  in  aqua  regia,  or  in  a  mixture  of 
hydrochloric  acid  and  potassium  chlorate.  The  proportion 
of  silver  is  generally  so  small  that  no  silver  chloride 
remains.  If  any  lead  chloride  is  separated  it  is  dissolved 
by  heating  in  water.  The  solution  is  treated  with  sulphu- 
retted hydrogen,  when  lead,  copper,  bismuth,  antimony, 
and  arsenic  are  deposited.  To  ascertain  that  the  arsenic 
is  completely  precipitated  the  liquid  is  heated  and  again 
treated  with  sulphuretted  hydrogen.  The  metallic  sul- 
phides are  digested  with  concentrated  yellow  ammonium 
hydrosulphide,  in  order  to  dissolve  the  arsenic  and  anti- 
mony sulphides. 

After  filtration  both  are  precipitated  by  hydrochloric 
acid,  and  separated  as  directed  under  arsenical  iron. 

The  undissolved  sulphides  of  copper,  lead,  and  bismuth 
are  allowed  to  become  air-dry,  and  are  then  detached  from 
the  filter,  which  is  incinerated  in  a  small  porcelain  crucible. 
Firstly,  these  ashes  and  then  the  total  sulphides  are  dis- 
solved in  nitric  acid.  The  sulphur,  which  is  not  quite 
pure,  is  filtered  off  and  gently  heated  in  a  porcelain 
crucible,  the  slight  residue  being  digested  again  with  nitric 
acid  and  added  to  the  main  solution  (if  lead  sulphate 
remains  unattacked  it  must  be  collected  on  a  weighed, 
filter).  The  nitric  solution  of  the  three  metals  is  concen- 


ASSAY   OF   NICKEL   SPEISS.  773 

trated  by  evaporation,  and  the  lead  separated  as  already 
directed.  The  filtrate  is  saturated  with  sodium  carbonate, 
potassa  is  added,  the  whole  heated  to  a  boil,  the  oxides 
are  filtered  off,  washed  slightly,  dissolved  in  the  smallest 
quantity  of  hydrochloric  acid,  and  the  bismuth  is  precipi- 
tated by  the  addition  of  much  water  as  basic  oxychloride, 
which  is  reduced  by  potassium-cyanide,  as  already  de- 
scribed. Copper  is  precipitated  from  the  filtrate  by  sul- 
phuretted hydrogen. 

In  the  filtrate  from  the  first  sulphuretted  hydrogen 
precipitate  there  are  still  found  iron  (as  ferrous  oxide), 
nickel,  cobalt,  and  zinc.  The  liquid  is  concentrated  to 
expel  sulphuretted  hydrogen  and  most  of  the  free  acid ; 
the  iron  is  peroxidised  by  the  addition  of  a  little  potassium 
chlorate,  diluted,  the  free  chlorine  expelled  by  heating 
with  a  few  drops  of  alcohol,  and  the  iron  oxide  is  separated 
from  zinc,  nickel,  and  cobalt  as  directed  for  arsenical 
nickel-glance,  &c. 

B.  Speiss  containing  much  Lead  or  Antimony. — The 
process  to  be  followed  is  tedious,  and  requires  much  care. 
The  substance,  finely  powdered,  is  decomposed  by  heating 
in  a  current  of  chlorine  gas. 

The  apparatus  requisite  consists  of  a  capacious  flask,  in 
which  the  necessary  chlorine  gas  is  evolved  from  a  mixture 
of  2  parts  black  oxide  of  manganese,  3  parts  of  common 
salt  and  dilute  sulphuric  acid  (1.^  to  2  parts  water  to  1 
part  of  the  monohydrated  acid).  The  flask  is  closed  with 
a  cork,  through  which  passes  a  tube  bent  twice  at  right 
angles.  Its  longer  leg  dips  into  concentrated  sulphuric 
acid  contained  in  a  second  flask,  where  the  gas  is  partially 
dried  and  whence  it  issues  to  pass  by  another  tube  into  a 
chloride  of  calcium  apparatus,  and  thence  into  the  bulb- 
tube  in  which  the  reaction  is  to  take  place.  The  tube  is 
tared,  from  1  to  2  grms.  of  the  finely-ground  sample  is 
inserted  into  the  bulb  through  its  wider  tube,  both  ends 
are  cleaned  with  a  feather,  so  that  none  remains  except  in 
the  bulb,  and  the  whole  is  weighed  to  find  the  exact  quantity 
which  has  been  taken  for  analysis.  The  shorter  tube  is 
then  connected  to  the  chloride  of  calcium  apparatus,  and 


774         THE  ASSAY  OF  NICKEL  AND  COBALT. 

the  longer,  or  bent  tube,  is  conducted  through  a  cork  into 
a  receiver,  which  resembles  a  Liebig's  bulb-tube  on  a  larger 
scale,  and  with  parallel  limbs.  It  is  filled  with  dilute 
hydrochloric  acid,  to  which  a  little  tartaric  acid  is  added, 
if  the  body  under  analysis  contains  antimony.  From  the 
second  limb  of  this  receiver  a  bent  tube  passes  into  a 
Woolfs  bottle,  and  dips  into  the  same  solution.  From 
the  other  aperture  passes  a  tube  which  carries  away  the 
escaping  chlorine.  When  all  parts  of  the  apparatus  are 
full  of  chlorine  heat  is  carefully  and  gradually  applied  to 
the  bulb,  which  must  not  reach  visible  redness.  After  the 
completion  of  the  operation  the  bulb  contains  the  non- 
volatile lead,  silver,  bismuth,  copper,  nickel,  cobalt  chlo- 
rides, and  in  part  those  of  iron  and  zinc.  They  are  dis- 
solved out  by  means  of  water  and  hydrochloric  acid  ; 
undecomposed  portions  of  the  sample  and  silver  chloride 
may  remain,  and  are  collected  upon  a  weighed  filter,  and 
after  weighing  treated  with  ammonia,  which  dissolves  the 
silver  chloride,  leaving  the  undecomposed  matter  behind. 
The  hydrochloric  solution  is  filtered  into  dilute  sulphuric 
acid,  evaporated,  and  the  lead  separated  as  lead  sulphate. 
The  filtrate  is  precipitated  with  sulphuretted  hydrogen, 
and  copper  and  bismuth  are  separated  by  dissolving  the 
sulphides  in  hydrochloric  acid,  to  which  a  little  nitric  acid 
is  added,  the  solution  concentrated  to  a  small  bulk,  the 
bismuth  precipitated  by  water,  the  basic  bismuth  chloride 
reduced  by  potassium  cyanide,  and  in  the  filtrate  the 
copper  precipitated  by  sulphuretted  hydrogen  in  the  ordi- 
nary manner.  The  filtrate  from  which  the  copper  and 
bismuth  sulphides  were  removed,  contains  iron,  zinc, 
nickel,  and  cobalt,  and  is  treated  as  already  pointed  out. 

From  the  volatile  chlorides  contained  in  the  liquid 
from  the  receivers  the  sulphuric  acid  is  removed  by  barium 
chloride,  and  any  excess  of  the  latter,  by  the  cautious  addi- 
tion of  sulphuric  acid.  Antimony  and  arsenic  are  precipi- 
tated by  sulphuretted  hydrogen,  and  separated  in  the  usual 
manner.  The  filtrate  contains  the  volatilised  portions  of 
iron  and  zinc,  which  are  also  dealt  with  by  ordinary 
methods. 


775 


CHAPTEE  XXIV. 

THE   ASSAY   OF   SULPHUR. 

THE  only  commercially  valuable  Sulphur-minerals  are  : — 

I.  Sulphurous  Earth  (native  sulphur). 

In  Sicily  these  minerals  are  divided  into  five  classes  : — 

1.  Very  rich  ores,  containing  32 — 34  per  cent,  sulphur 

2.  Rich  „  „          24-26      „ 

3.  Good  „  „          16-18      „ 

4.  Middling     „  „  8—  9      „ 

5.  Poor  „  „  3—5      „  „ 

II.  Iron  and  Copper  Pyrites  (FeS2),  and  (Cu2S,Fe2S3). 

These  ores  are  used  to  a  very  large  extent  for  the 
manufacture  of  sulphuric  acid. 

In  order  to  approximatively  estimate  the  value  of  ores 
of  the  first  class  for  such  manufacture,  the  following  method 
of  assay  may  be  used. 

Assay  by  Distillation. — A  certain  quantity  of  the  pul- 
verised sulphurous  earth  is  heated  in  a  glass  retort,  which 
is  furnished  with  a  receiver.  The  retort  is  then  heated, 
gradually  raising  the  temperature,  till  no  more  sulphur  is 
evolved.  The  latter  will  collect  in  the  neck  of  the  retort 
and  receiver,  which  may  be,  in  all  cases,  of  glass,  and  must 
be  kept  cool. 

The  sulphur  derived  from  sulphurous  earth  is  generally 
pure,  whilst  that  from  pyrites  frequently  contains  arsenic 
and  selenium,  and  sometimes  traces  of  thallium. 

ASSAY   OF   IRON   AND    COPPER    PYRITES. 

A.  Assay  of  Sulphur  in  the  Dry  Way. — Fuse  the 
weighed  ore  with  a  weighed  quantity  of  anhydrous  sodium 
carbonate,  twice  as  much  potassium  chlorate  as  ore,  and 


776  THE   ASSAY   OF   SULPHUR. 

from  12  to  20  times  as  much  sodium  chloride  (added  to 
moderate  the  action)  ;  carbonic  acid  is  expelled,  potassium 
chloride  formed,  and  all  the  sulphur  converted  into  sodium 
sulphate  ;  by  dissolving  the  residue  in  water  and  esti- 
mating alkalimetrically  the  unaltered  sodium  carbonate  by 
a  standard  acid  solution,  the  portion  converted  into  sul- 
phate, and  hence  the  sulphur  in  the  ore,  is  known.  Besides 
the  difficulty  of  preventing  loss  by  deflagration,  this  method 
is  open  to  the  small  errors  caused  by  the  reckoning  all 
arsenic  present  to  be  sulphur  :  this,  however,  is  usually  of 
no  moment  for  commercial  purposes  ;  and  calcium  carbo- 
nate in  the  ore  may,  if  required,  be  previously  dissolved 
out  by  dilute  hydrochloric  acid. 

In  performing  fusions  of  sulphur  compounds  with 
nitre  or  potassium  chlorate  the  operator  must  bear  in  mind 
a  source  of  error,  first  pointed  out  by  Dr.  David  S.  Price, 
in  consequence  of  sulphur  compounds  being  contained  in 
the  coal-gas  which  frequently  serves  as  fuel  in  these  experi- 
ments. By  exposing  a  small  quantity  of  fused  nitre,  on 
the  outside  of  a  platinum  capsule,  to  the  flame  of  a  Bunsen 
gas-burner  for  three-quarters  of  an  hour,  Dr.  Price  suc- 
ceeded in  detecting  the  presence  of  sulphuric  acid  to  an 
amount  equivalent  to  12  milligrammes  of  sulphur.  This 
sulphuric  acid  had  been  formed  by  the  oxidation  of  the 
sulphur  in  the  coal-gas,  and,  when  dissolved  in  water,  it 
gave  an  immediate  precipitate  with  chloride  of  barium. 
By  making  a  similar  experiment  with  the  use  of  a  spirit- 
lamp  as  the  source  of  heat,  no  trace  of  potassium  sulphate 
was  formed  ;  nor  was  any  appreciable  amount  of  sulphuric 
acid  generated  in  another  trial  made  by  fusing  a  small 
quantity  of  nitre  inside  a  platinum  capsule  heated  over 
gas  ;  but  whenever  the  fused  salt  crept  over  the  edges  of 
the  capsule,  some  potassium  sulphate  was  sure  to  be  formed. 
This  observation  may  become  a  matter  of  importance  when 
the  amount  of  sulphur  in  pig-iron  is  determined  by  fusion 
with  pure  nitre,  for  the  author  has  remarked  that  samples 
containing  much  manganese  are  especially  liable  to  impart 
to  the  fused  salt  a  tendency  to  creep  up  and  escape  over  the 
sides  of  the  crucible. 


ASSAY   OF   SULPHUR   IX   PYRITES.  777 

B.  Assay  of  Sulphur  in  the  Wet  Way. — Mr.  C.  E.  A. 
Wright  recommends  the  following  process  as  being  the  one 
best  adapted  for  commercial  purposes : — A  known  weight 
of  the  ore  reduced  to  fine  powder  is  oxidised  (best  in  a 
small  flask  with  a  funnel  in  the  mouth  to  avoid  loss  by 
spirting,  and  heated  on  a  sand-bath),  either  by  strong 
nitric  acid,  or  aqua  regia,  perfectly  free  from  sulphuric 
acid ;  after  the  oxidation  is  complete,  the  liquid  is  evapo- 
rated down  as  far  as  possible  to  expel  the  majority  of  the 
remaining  nitric  or  hydrochloric  acid  ;  the  residue  is  boiled 
with  a  little  water,  and  almost  but  not  quite  neutralised  by 
ammonia  ;  a  solution  of  barium  chloride  of  known  strength 
is  then  added  until  no  further  precipitate  is  produced,  the 
exact  point  being  found  by  filtering  off  a  little  of  the  liquid 
after  each  addition  of  barium  chloride,  and  adding  to  it  a 
few  more  drops  of  the  standard  solution,  care  being  always 
taken,  in  case  of  a  further  precipitate  being  thus  produced, 
to  add  this  filtrate  to  the  original  solution,  and  mix  well 
before  filtering  a  second  time.  In  case  of  overstepping  the 
mark,  it  is  convenient  to  have  at  hand  a  solution  of  sodium 
sulphate  of  strength  precisely  equal  to  that  of  the  barium 
chloride  ;  this  solution  may  then  be  cautiously  added, 
with  repeated  filtration  and  examination  of  the  filtrate 
with  the  sulphate  solution,  until  the  point  is  just  reached 
when  addition  of  sulphate  solution  produces  no  further 
precipitate ;  by  subtracting  the  volume  of  sulphate  solu- 
tion thus  used  from  the  total  volume  of  barium  solution 
added,  the  exact  quantity  of  this  latter  consumed  is 
known.  If  1  grm.  of  sulphur  ore  be  taken,  and  32 -5 
grms.  of  pure  anhydrous  barium  chloride  be  dissolved  in 
a  litre  of  fluid,  each  cubic  centimetre  of  barium  solution 
used  will  represent  ^  per  cent,  of  sulphur  in  the  ore 
examined :  22*19  grms.  of  anhydrous  sodium  sulphate 
being  dissolved  to  a  litre  for  the  second  solution.  In  case 
of  lead  being  contained  in  the  ore,  an  error  is  introduced 
from  the  formation  of  insoluble  lead  sulphate ;  as  lead, 
however,  rarely  occurs  in  any  perceptible  quantity,  this 
error  is  negligible,  the  process  only  giving  approximate 
results. 


778  THE   ASSAY   OF   SULPHUR. 

Where  greater  accuracy  is  required,  it  is  advisable  to 
precipitate  the  sulphuric  acid  formed  from  the  original 
liquid  (filtered  from  insoluble  residue)  by  barium  nitrate 
or  chloride,  and  to  weigh  the  barium  sulphate  produced. 
Instead  of  oxidising  by  acids,  the  powdered  ore  may  be 
suspended  in  caustic  potash  (free  from  sulphate),  and 
oxidised  by  passing  washed  chlorine  into  the  liquid ;  lead, 
being  converted  into  dioxide,  is  thus  rendered  non-injurious ; 
the  alkaline  liquid  obtained  is  acidified,  and  precipitated 
by  chloride  of  barium  as  before.  In  the  volumetric  deter- 
mination usually  pursued,  a  curious  circumstance  is  occa- 
sionally observable  when  much  free  acid  exists  in  the 
solution,  viz.,  that  a  point  may  be  reached  when  the  fil- 
tered liquid  is  clear,  and  remains  so  even  on  standing  for 
a  short  time,  but  yields  a  cloud,  or  even  a  precipitate,  on 
the  addition  either  of  barium  solution  or  sulphate  solution  ; 
this  source  of  error  is  mostly  avoidable  by  nearly  neutra- 
lising the  free  acid  with  ammonia. 

Instead  of  chlorine,  hypochlorous  acid  may  be  used  to 
transform  the  sulphur  of  pyrites  into  sulphuric  acid,  which 
is  then  estimated  by  barium  chloride.  Finely  pulverise 
the  mineral  and  suspend  it  in  water,  through  which  a 
current  of  gaseous  hypochlorous  acid,  or.  better  still, 
hypochloric  acid  is  passed ;  this  entirely  dissolves  the 
pyrites.  Hypochlorous  acid  is  prepared  by  heating  a  milk 
of  calcium  carbonate  through  which  a  current  of  chlorine 
is  passed  to  saturation.  Hypochloric  acid  is  obtained  by 
heating  in  a  water-bath  a  tube,  supplied  with  a  cork  and 
delivery  tube,  and  containing  a  mixture  of  nine  equivalents 
of  oxalic  acid  and  one  equivalent  of  chlorate  of  potash. 

Mr.  A.  H.  Pearson  has  given  the  following  very  accu- 
rate method  of  estimating  sulphur  in  pyrites -.—Weigh  out 
1  grm.  or  less  of  the  powdered  ore,  place  the  powder  in  a 
porcelain  dish,  together  with  a  small  quantity  of  potassium 
chlorate,  pour  upon  it  some  50  c.c.  of  pure  nitric  acid  of 
39°  B.,  and  cover  the  mixture  with  an  inverted  glass  funnel 
with  bent  stem.  Set  the  dish  upon  a  water-bath,  and 
heat  the  water  to  boiling.  From  time  to  time  throw 
crystals  of  potassium  chlorate  into  the  hot  acid.  By  adding 


ASSAY   OF   SULPHUR   IX   PYRITES.  779 

rather  large  crystals  of  the  .chlorate  at  frequent  intervals, 
it  is  easy  to  oxidise  the  whole  of  the  sulphide  in  half  an 
hour  ;  but,  since  the  solution  obtained  in  that  case  is 
highly  charged  with  saline  matter,  it  will  usually  be  found 
more  advantageous  to  use  less  of  the  potassium  chlorate, 
and  to  allow  a  somewhat  longer  time  for  the  process  of 
oxidation. 

When  all  the  sulphur  has  been  oxidised,  rinse  the 
funnel  with  water,  and  remove  it  from  the  dish.  Evapo- 
rate the  liquid  to  a  small  bulk,  then  add  to  it  a  little 
concentrated  hydrochloric  acid,  and  again  evaporate  to 
absolute  dryness,  in  order  to  render  silicic  acid  insoluble. 
Moisten  the  residue  with  concentrated  hydrochloric  acid, 
mix  it  with  water,  and  filter  to  separate  silicic  acid  and 
gangue. 

To  the  filtrate  from  the  silicic  acid  add  a  quantity  of 
solid  tartaric  acid,  about  as  much  as  that  of  the  pyrites 
originally  taken ;  heat  the  liquid  almost  to  boiling,  and 
add  to  it  an  excess  of  barium  chloride,  to  precipitate  the 
sulphuric  acid.  After  the  barium  sulphate  has  been 
allowed  to  subside,  wash  it  thoroughly  by  decantation, 
first  with  hot  water,  and  afterwards  with  a  dilute  solution 
of  ammonium  acetate  (the  latter  may  be  prepared  at  the 
moment  of  use  by  mixing  ammonia-water  and  acetic  acid). 
The  purpose  of  the  ammonium  acetate  is  to  dissolve  any 
barium  nitrate  which  may  adhere  to  the  sulphate ;  that  of 
the  tartaric  acid  is  to  prevent  the  precipitation  of  iron 
compounds  together  with  the  barium  sulphate.  In  an 
experiment  where  O7  grm.  of  pyrites  was  oxidised  with 
potassium  chlorate  and  nitric  acid,  and  the  filtrate  from 
silica  was  acidulated  with  hydrochloric  acid  without  the 
addition  of  tartaric  acid,  there  was  thrown  down,  on  the 
addition  of  barium  chloride,  a  bright  yellow  precipitate, 
which  became  darker-coloured  when  the  solution  was 
boiled.  It  was  not  only  found  to  be  impossible  to  wash 
out  the  iron  with  which  this  precipitate  was  contaminated, 
but  the  consistency  of  the  precipitate  was  such  that  it  was 
a  difficult  matter  even  to  wash  away  the  saline  liquor  in 
which  it  was  formed. 


780  THE    ASSAY   OF    SULPHUR. 

M.  A.  Houzeau,  in  his  so-called  gravi- volume  trie  pro- 
cess, attacks  1  gramme  of  the  powdered  ore  with  a 
mixture  of  4  parts  pure  potassium  nitrate,  and  3  parts 
sodium  carbonate,  likewise  pure.  The  saline  mass  is 
dissolved  in  hot  water,  and  the  ferric  oxide  filtered  from 
the  alkaline  sulphate.  The  washing  waters  are  added  to 
the  filtrate,  and,  after  cooling,  it  is  made  up  with  distilled 
water  to  half  a  litre.  A  portion  is  then  taken  (10  c.c.) 
and  acidulated  with  a  few  drops  of  pure  acetic  acid,  and 
the  sulphuric  acid  is  rapidly  determined,  as  the  author 
has  elsewhere  indicated  for  selenitic  waters,  by  making  use 
of  a  standard  solution  of  barium  chloride,  applied  by  the 
aid  of  the  gravi-volumeter  in  place  of  the  ordinary  burette, 
the  use  of  which,  in  such  determinations,  yields  merely 
erroneous  results.  In  the  gravi-volumeter  the  weight  of 
the  standard  solution  shows  the  quantity  of  the  reagent 
which  has  been  used.  But  each  drop  of  the  barytic 
liquid  delivered  by  the  gravi-volurneter  weighs  at  the 
temperature  of  13°  exactly  0-050  grm. 

In  the  Freiberg  works,  1  grm.  of  finely-ground  ore  is 
mixed  with  3  grms.  anhydrous  sodium  carbonate,  and  an 
equal  weight  of  saltpetre.  This  mixture  is  placed  in  an 
iron  crucible,  melted  in  a  muffle.  At  a  red  heat,  the  mass 
is  dissolved  in  hot  water,  and  the  liquid  is  filtered  into 
a  beaker,  in  which  there  is  a  little  hydrochloric  acid  to 
saturate  the  excess  of  soda.  The  liquid,  which  should 
have  an  acid  reaction,  is  then  boiled  for  a  short  time,  and 
the  sulphuric  acid  is  determined  volumetrically  with  a 
solution  of  barium  chloride  standardised,  so  that  1  c.c. 
indicates  2  per  cent,  of  sulphur. 

B.  Deutecom  adopts  the  following  process: — 1  grm. 
pyrites  was  mixed  in  a  large  covered  crucible  with  8  grms. 
of  a  mixture  of  equal  parts  potassium  chlorate,  sodium 
carbonate,  and  sodium  chloride.  The  crucible  is  heated  at 
first  gently,  so  as  to  dry  the  contents,  which  are  after- 
wards melted  at  a  high  temperature.  The  mass,  when 
cold,  is  treated  with  boiling  water,  and  the  solution,  to- 
gether with  the  deposit,  is  introduced  into  a  measuring- 
flask  of  200  c.c.,  filled  up,  filtered,  and  the  sulphuric  acid 


ASSAY   OF   SULPHUR   IX   PYRITES.  781 

is  determined  in  aliquot  parts,  say  50  c.c.  The  inso- 
luble residue  does  not  retain  any  sulphuric  acid.  In  this 
manner  the  use  of  nitric  acid  is  evaded.  The  decompo- 
sition of  the  potassium  chlorate  is  complete. 

In  assaying  pyrites  for  sulphur  only  by  fusion,  Mr. 
P.  Holland  has  obtained  good  results  by  the  following 
process,  which  may  be  useful  in  such  laboratories  as  do 
not  possess  large  platinum  crucibles.  A  test-tube,  or 
piece  of  sealed  combustion  tube,  about  6  inches  long  and 
half  an  inch  in  internal  width,  is  fitted  with  a  cork  and 
delivery  tube,  the  latter  bent  at  a  right  angle,  and  long 
enough  to  reach  to  the  bottom  of  the  flask  in  which  it  is 
intended  to  make  the  titration.  The  fusion  mixture  con- 
sists of  equal  parts  of  nitre  and  ignited  sodium  bicar- 
bonate, both  free  from  sulphur,  dry,  and  in  fine  powder. 
Nine  to  ten  grammes  are  taken  in  an  operation,  together 
with  one  of  pyrites ;  the  latter  must  be  in  exceedingly  fine 
powder.  The  two  are  mixed  in  a  warm  porcelain  dish  or 
agate  mortar,  and  transferred  to  the  tube  without  loss. 
The  delivery  tube  is  then  inserted,  with  its  extremity 
dipping  into  the  flask.  A  channel  is  made  on  the  surface 
of  the  mixture,  and  the  tube,  suitably  supported,  is  heated 
by  small  portions  at  a  time  with  a  Bunsen  gas  flame,  com- 
mencing as  usual  with  the  anterior  portion.  When  the 
operation  is  progressing  favourably,  the  deflagration 
proceeds  for  a  few  seconds  after  removing  the  flame. 

There  is  no  danger  to  be  apprehended,  and  the  tube 
does  not  crack  or  blow  out  with  proper  care.  When  the 
tube  has  been  heated  throughout,  and  the  deflagration 
has  ceased,  it  is  then  more  strongly  heated  with  a  Hera- 
path  or  powerful  gas  flame.  It  is  a  good  plan  at  this 
stage  to  slip  a  coil  of  wire  gauze  over  the  tube,  which 
helps  to  accumulate  the  heat.  It  is  not,  however,  neces- 
sary that  the  contents  should  be  fused  a  second  time ;  at 
least  this  has  not  been  done  in  experiments  appended. 
The  sulphur  ores  examined  have  yielded  their  sulphur 
readily. 

The  gaseous  products  of  the  combustion,  which 
mechanically  carry  over  with  them  small  quantities  of 


782  THE   ASSAY   OF   SULPHUR. 

sulphates  or  sulphuric  acid,  being  heavier  than  air,  collect 
in  the  flask,  and  are  washed  by  shaking  with  a  little 
water,  closing  the  flask  with  the  palm  of  the  hand.  The 
delivery  tube  is  also  washed.  That  containing  the  fused 
mass  is  carefully  broken  and  put  in  the  flask,  together 
with  sufficient  hydrochloric  acid  to  dissolve  nearly  the 
whole  of  the  iron  oxide  ;  then  ammonia  is  added,  until  a 
precipitate  of  oxide  reappears  ;  and  lastly,  as  much  hydro- 
chloric acid  and  water  as  is  necessary  to  bring  the  fluid 
to  the  conditions  which  were  obtained  when  the  barium 
solution  was  standardised.  The  author  has  used  2  c.c.  of 
free  acid,  and  the  total  volume  of  solution  was  200  c.c. 


783 


CHAPTER  XXY. 

DISCRIMINATION   OF   GEMS  AND   PRECIOUS   STONES. 

SIMPLE  characteristics  of  and  means  of  recognising  many 
gems  and  precious  stones  have  been  given  at  page  287,  in 
the  section  on  the  discrimination  of  minerals. 

The  present  chapter  contains  much  information  which 
could  not  appropriately  be  introduced  in  the  previous 
chapter,  which  was  intended  chiefly  for  the  use  of  tra- 
vellers and  explorers.  Some  trifling  repetitions  occur 
purposely  to  save  the  inconvenience  of  referring  back. 

The  principal  sources  of  recognition  are  colour,  crys- 
talline form,  specific  gravity,  and  hardness.  In  the  present 
chapter  will  be  introduced  all  the  most  constantly  oc- 
curring natural  forms  of  the  gems  and  precious  stones 
mentioned. 

The  specific  gravity  or  density  of  a  substance  is  the 
proportion  of  its  weight  to  its  volume,  and  it  forms  a 
characteristic  property  of  substances.  A  full  description 
of  the  method  of  taking  specific  gravities  has  been  given 
at  pages  236,  237. 

COLOURLESS  STONES. 

THE    DIAMOND. 
(See  also  p.  252.) 

Specific  gravity,  3-48  to  3-52;  hardness,  10.  The 
diamond  is  the  hardest  of  all  known  substances.  The 
diamond  is  the  only  substance  which  is  capable  of  cutting 
glass,  although  most  gems  will  scratch  glass  ;  hence  it  is 
the  utmost  term  of  hardness.  When  cut  and  polished,  it 
is  the  most  brilliant  gem.  It  frequently  becomes  phos.- 


784  GEMS  AND   PEEGIOUS   STONES. 

phorescent  on  exposure  to  light.  The  greater  number  of 
diamonds  are  limpid  and  colourless,  but  many  coloured 
specimens  are  found ;  as  rose,  yellow,  orange,  blue,  green, 
brown,  or  even  black.  It  sometimes  occurs  in  regular 
crystals,  octahedrons,  dodecahedrons,  and  more  complex 
forms  ;  see  figs.  131,  132,  133,  134. 

The  crystalline  faces  are  often  curved.  The  cleavage 
is  octahedral  and  highly  perfect ;  hence,  although  dia- 
monds are  so  exceedingly  hard,  they  are  very  brittle,  owing 
to  their  tendency  to  facile  cleavage.  Like  most  gems,  they 

FIG.  131.  FIG.  132. 


FIG.  134. 

••M 
FIG.  133. 


become  electrical  by  friction  ;  but  it  has  been  remarked 
that  other  gems  do  not,  unless  they  have  been  previously 
polished. 

Composition  (C)  :  Pure  carbon. 

Speaking  of  diamonds,  Professor  Orton  says  that  few 
things  are  so  unpromising  and  unattractive  as  these  gems 
in  their  native  state.  Hence  their  slow  discovery.  There 
is  little  doubt  that  diamonds  exist  in  many  places  as  yet 
unknown,  or  where  their  presence  is  unsuspected.  It  is 
very  difficult  for  the  unpractised  eye  to  distinguish  them 
from  crystals  of  quartz  or  topaz.  The  colour  constitutes 
the  main  difficulty  in  detecting  their  presence.  They  are 
of  various  shades  of  yellowish-brown,  green,  blue,  and  rose- 


COLOURLESS   STONES.  785 

red,  and  thus  closely  resemble  the  common  gravel  by  which 
they  are  surrounded.  Often  they  are  not  unlike  a  lump 
of  gum  arabic,  neither  brilliant  nor  transparent.  The 
finest,  however,  are  colourless,  and  appear  like  rock 
crystals. 

In  Brazil,  where  great  numbers  of  diamonds,  chiefly  of 

small  size,  have  been  discovered,  the  method  of  searching 

for  them  is  to  wash  the  sand  of  certain  rivers  in  a  manner 

precisely  similar   to   that   employed   in   the   gold   fields, 

namely,  by  prospecting  pans.      A  shovelful  of  earth  is 

thrown  into  the  pan,  which  is  then  immersed  in  water,  and 

gently  moved  about.    As  the  washing  goes  on,  the  pebbles, 

dirt,  and  sand  are  removed,  and  the  pan  then  contains 

about  a  pint  of  thin  mud.     Great  caution  is  now  observed, 

and  ultimately  there  remains  only  a  small  quantity  of  sand. 

The  diamonds  and  particles  of  gold,  if  present,  sink  to  the 

bottom,  being  heavier,  and  are  selected  and  removed  by 

the  practised  fingers  of  the  operator.     But  how  shall  the 

gems  be  detected  by  one  who  in  a  jeweller's  shop  could 

not  separate  them  from   quartz  or  French  paste?     The 

difficulty  can  only  be  overcome  by  testing  such  stones  as 

may  be  suspected  to  be  precious.     Let  these  be  tried  by 

the  very  sure  operation  of  attempting  to  cut  with  their 

sharp  corners  glass,  crystal,  or  quartz.     When  too  minute 

to  be  held  between  the  finger  and  thumb,  the  specimens 

may  be  pressed  into  the  end  of  a  stick  of  hard  wood  and 

run  along  the  surface  of  window  glass.     A  diamond  will 

make  its  mark,  and  cause,  too,  a  ready  fracture  in  the  line 

over  which  it  has  travelled.     It  will  also  easily  scratch 

rock  crystal,  as  few  crystals  will. 

But  a  more  certain  and  peculiar  characteristic  of  the 
diamond  lies  in  the  form  of  its  crystals.  The  ruby  and 
topaz  will  scratch  quartz,  but  no  mineral  which  will  scratch 
quartz  has  the  curved  edges  of  the  diamond.  In  small  crys* 
tals  this  peculiarity  can  be  seen  only  by  means  of  a  magnify- 
ing glass ;  but  it  is  invariably  present.  Interrupted,  convex1, 
or  rounded  angles  are  sure  indications  of  genuineness 
Quartz  crystal  is  surrounded  by  six  faces,  the  diamond  by 
four.  The  diamond  breaks  with  difficulty ;  and  hence  a 

SE 


786  GEMS  AND   PRECIOUS  STONES. 

test  sometimes  used  is  to  place  the  specimen  between  two 
hard  bodies,  as  a  couple  of  coins,  and  force  them  together 
with  the  hands.  Such  a  pressure  will  crush  a  particle  of 
quartz,  but  the  diamond  will  only  indent  the  metal. 

The  imperfections  of  the  diamond,  and,  in  fact,  of  all 
cut  gems,  are  made  visible  by  putting  them  into  oil  of 
cassia,  when  the  slightest  flaw  will  be  seen. 

If  a  rough  diamond  resemble  a  drop  of  clear  spring 
water,  in  the  middle  of  which  you  perceive  a  strong  light ; 
or  if  it  has  a  rough  coat,  so  that  you  can  hardly  see  through 
it,  but  white,  and  as  if  made  rough  by  art,  yet  clear  of 
flaws  or  veins  ;  or  if  the  coat  be  smooth  and  bright,  with 
a  tincture  of  green  in  it, — it  is  a  good  stone.  If  it  has  a 
milky  cast  or  a  yellowish-green  coat,  beware  of  it.  Eough 
diamonds  with  a  greenish  crust  are  the  most  limpid  when 
cut. 

Diamonds  are  found  in  loose  pebbly  earth,  along  with 
gold,  a  little  way  below  the  surface,  towards  the  lower 
outlet  of  broad  valleys,  rather  than  upon  the  ridges  of 
the  adjoining  hills. 

Prof.  Silliman,  on  examining  with  the  microscope  a 
small  parcel  of  the  sand  resulting  from  the  hydraulic  treat- 
ment of  ores,  found  that  they  abounded  in  fine  colourless 
zircons,  along  with  crystals  of  topaz,  fragments  of  quartz, 
grains  of  chrome  iron,  and  titanic  acid,  and  globular  bodies 
of  a  very  high  refractive  power,  which  he  believes  to  be 
diamonds. 

Mr.  J.  Torry,  in  a  single  sample  of  the  sands  washed 
from  the  gold  ores  of  Nicaragua,  found  twenty  mineral 
species,  some  of  them  very  rare. 

For  determining  the  specific  gravity  of  certain  minerals, 
and  separating  diamond  dust  or  small  diamonds  and  other 
gems  from  quartz,  sand,  &c.,  Mr.  E.  Sonstardt*  uses  a 
solution  in  water  of  pure  potassium  iodide  and  pure  mer- 
curic iodide  in  cold  water.  It  should  be  diluted  to  such 
a  strength  that  quartz  will  just  float  in  it.  (See  ante, 
page  237.) 

*  <  Chemical  News/  March  20,  1874. 


COLOURLESS   STONES. 


787 


QUARTZ 


Specific  gravity,  2-55  to  2'7  ;  hardness,  7..  Quartz 
occurs  in  many  forms,  and  has  often  by  inexperienced 
persons  been  mistaken  for  the  diamond,  owing  to  the  lustre 
of  its  crystals  and  its  considerable  hardness.  It,  however, 
can  always  be  distinguished  from  the  diamond  by  its  crys- 


FIG.  137. 


FlG.  135. 


FIG.  136. 


FIG.  138. 


FIG.  139. 


talline  faces,  hardness,  and  specific  gravity  (see  example  in 
Table  I.). 

It  usually  occurs  in  six-sided  prisms,  more  or  less 
modified,  terminated  with  six-sided  pyramids.  Traces  of 
cleavage  are  seldom  or  ever  apparent.  Some  of  its  salient 
forms  are  shown  in  figs.  135,  136, 137,138, 139, 140, 141. 

3  E  2 


788 


GEMS  AND   PRECIOUS   STONES. 

FIG.  140. 

""""""  FIG.  141. 


Some  crystals  are  as  pellucid  as  glass ;  others,  however,, 
assume  all  the  shades  of  colour  mentioned  in  the  case  of 
the  diamond. 

Composition  (Si02) :  Pure  silica  or  silicic  acid. 


WHITE   ZIRCON. 


Specific  gravity,  4'44  to  4*8  ;  hardness,  7 '5.  This  stone 
is  often  found  crystallised  in  nature  in  four-sided  prisms, 
terminated  by  four-sided  or  rhomboidal  or  triangular 


FIG.  142. 


FIG.  143. 


FIG.  144. 


pyramids,  and  other  forms.     See  figs.  142,  143,  144,  145, 
146,  147. 

These  stones  are  often  employed  in  jewellery  under  the 
name  of  6  rough  diamonds.'  They  often  occur  brownish- 
red  and  brown,  red,  yellow,  and  grey ;  these  varieties  will 


COLOURLESS   STONES.  78£ 

be  treated  under  their  appropriate  heads.    It  can  be  readily 
distinguished  from  the  diamond  and  quartz  by  hardness 

FIG.  145.  FIG.  H6.  FIG.  147. 


and  specific  gravity ;  also  by  the  action  of  strong  hydro- 
chloric acid,  which,  if  dropped  on  the  diamond  or  quartz, 
and  allowed  to  remain  for  a  little  time,  produces  no  change, 
but  if  a  zircon  be  so  treated,  the  spot  on  which  the  acid 
was  placed  remains  dull. 

Composition  (Zr203,Si02)  : — 

Zirconia 67*2 

Silicic  acid 33-5 


100-7 
WHITE   SAPPHIRE. 

Specific  gravity,  3*97  to  4'27 ;  hardness,  9.  This  stone^ 
in  hardness,  is  next  to  the  diamond.  It  occurs  variously 
coloured  ;  other  colours  will  be  discussed  under  their  ap- 
propriate heads.  It  crystallises  in  the  rhombohedric  system, 
usually  in  six-sided  prisms,  but  often  so  very  rough  as  not 
to  be  readily  distinguishable.  May  be  distinguished  by 
gravity  and  hardness  from  all  the  preceding. 

Composition  (A1203) : — Pure  alumina. 

WHITE   TOPAZ. 

Specific  gravity,  3 -54  ;  hardness,  9.  This  variety  of 
topaz,  known  for  its  limpidity  by  the  term  '  gouttes  d'eau,' 
when  polished  has  nearly  the  same  lustre  as  the  diamond ; 


79D 


GEMS  AND   PKECIOUS   STONES 


the  topaz,  however^  occurs  of  many  colours — see  hereafter. 
It  crystallises  in  the  right  rectangular  prismatic  system. 
Some  of  its  natural  forms  are  shown  in  figs.  148, 149, 150, 
151,152,153. 

It  is  readily  rendered  electric,  and  retains  its  electricity 
for  a  very  considerable  time  ;  it  is  also  pyro-electric,  or 
becomes  electric  when  heated, — a  property  by  which  it  is 


FIG.  148. 


FIG.  149. 


FIG.  150. 


FIG.  151. 


FIG.  152. 


FIG. 


distinguished  from  the  diamond,  its  specific  gravity  being 
so  similar  that  it  cannot  be  made  available  as  a  means  of 
discriminating  between  the  two  stones.  From  the  other 
stones  in  this  group,  with  the  exception  of  the  sapphire^ 
it  is  readily  distinguished  by  its  hardness  and  gravity,  and 
from  the  latter  by  its  gravity  and  pyro-electricity. 
Composition : — 

Silica        3       .         .         .         .         .         .     34-2 

Alumina   .        .         .  .         .         .     57*5 

Fluorine     .         .       •.  .      7-8 


COLOURLESS  STONES. 


791 


TABLE  I. 
COMPARATIVE  TABLE  OF  THE  WEIGHTS  OP  COLOURLESS  STONES 

WEIGHED   IN  AlR  AND   WATER. 


Weight  in 

Weight  in  Water 

Air 

White 

White 

White 

White 

White 

Grains 

Zircon 

Sapphire 

Topaz 

Diamond 

Quartz 

1 

0-775 

0-766 

0-716 

0-715 

0-611 

4 

3-10 

3-06 

2-86 

2-86 

2-42 

8 

6-20 

6-12 

5-72 

5-72 

4-86 

12 

9-30 

9-18 

8-58 

8-58 

7-31 

16 

12-40 

12-25 

11-55 

11-45 

9-75 

20 

15-50 

15-31 

14-42 

14-31 

12-19 

24 

18-60 

18-37 

17-28 

17-17 

14-64 

28 

21-70 

21-44 

20-16 

20-13 

17-08 

32 

24-80 

24-51 

23-01 

22-90 

19-53 

36 

27-90 

27-57 

25-88 

25-76 

11-98 

40 

31-00 

30-64 

28-75 

28-63 

24-43 

44 

34-10 

33-71 

31-61 

31-49 

26-88 

48 

37-20 

36-76 

34-47 

34-35 

29-32 

52 

40-30 

39-82 

37-34 

37-21 

31-77 

66 

43-40 

42-89 

40-20 

40-17 

34-21 

60 

46-50 

45-95 

43-06 

42-94 

36-66  , 

64 

49-60 

49-01 

45-93 

45-80 

39-11 

68 

52-70 

52-07 

48-90 

48-66 

41-56 

72 

55-80 

55-14 

51-77 

51-52 

44-00 

76 

58-90 

58-21 

54-63 

54-38 

46-44 

80 

62-00 

61-28 

57-49 

57-24 

48-88 

84 

65-10 

64-34 

60-35 

60-12 

51-32 

88 

68-20 

67-41 

63-22 

62-97 

53-76 

92 

71-30 

70-47 

66-08 

65-30 

56-21 

96 

74-40 

73-54 

68-94 

68-69 

58-65 

100 

77-50 

76-60 

71-80 

71-55 

61-09 

Specific 
Gravity 

4-44 

4-27 

3-54 

3-52 

.,  :  ,.2-S5 

Example  of  the  use  of  Table  I* — A  colourless  stone, 
weighing  40  grains  in  air,  is  reduced  to  24*43  in  water. 
Look  in  the  first  column  to  40,  and  then  trace  along  its 
horizontal  line  until  a  number  very  nearly  approaching 
24-43  is  found  ;  refer  then  to  the  heading  of  the  table, 
above  the  number  found,  and  the  name  there  expressed 
will  be  that  of  the  stone  examined.  Supposing,  however, 
the  weight  of  the  stone  be  41  grains,  still  the  number 
24-43  will  be  the  nearest  in  the  table,  and  -611  must  be 
added  to  it,  as  that  sum  would  be  the  weight  of  41  grains 

*  The  Tables  of  Comparatiye  Weights  were  calculated  by  Brard. 


792  GEMS  -AND    PRECIOUS  STONES. 

of  quartz  or  water.  From  the  numbers  obtained  by  cal- 
culation also  can  the  specific  gravity  be  determined.  If 
this  course  be  pursued,  refer  to  the  bottom  line  of  the 
table  for  a  corresponding  number,  and  to  the  heading  of  the 
table  for  the  name  of  the  stone.  When  the  weight  is  any 
even  number  of  grains  (that  is,  without  fractions),  the 
readiest  way  is  to  refer  to  the  table  (first  column)  for  the 
number  of  grains,  and  then  to  the  horizontal  line  to  corre- 
sponding number  obtained,  which  is  the  weight  in  water. 

Diamond  and  topaz,  however,  have  very  nearly  equal 
densities,  and  a  second  characteristic  must  be  had  recourse 
to  in  order  to  determine  the  nature  of  two  stones  which 
have  an  equal  weight  in  water.  This  auxiliary  character 
is  the  development  of  electricity  by  heat,  a  phenomenon 
exhibited  by  the  topaz  but  not  by  the  diamond.  The  test 
of  hardness  may  be  also  resorted  to. 

YELLOW  STONES. 
"YELLOW   ZIRCON    ( JARGON). 

The  crystalline  form,  characteristics,  and  composition 
of  this  stone  have  been  described  under  the  head  '  White 
Zircon.' 

YELLOW   SAPPHIRE. 

Characteristics,  &c.,  described  under  '  White  Sapphire.' 

CYMOPHANE   (CHRYSOBERYL). 

Specific  gravity,  3*65  to  3'89 ;  hardness,  8-5.  The 
cymophane  is  nearly  as  hard  as  the  sapphire,  harder  than 
the  topaz  and  the  emerald  ;  it  readily  scratches  quartz. 
Its  colour  is  greenish-yellow,  and  has  been  placed  in  the 
list  of  yellow  stones  rather  than  green,  because  usually  the 
yellowish  tint  is  the  most  decided.  This  tint,  which  is  very 
agreeable  in  itself,  is  often  relieved  by  a  small  spot  of  light 
of  a  bluish-white  tinge,  which  moves  from  point  to  point 
of  the  stone  as  the  position  of  the  latter  is  varied.  It  is 


YELLOW   STONES. 


793 


rarely  found  in  regular  crystals,  but  more  generally  occurs 
in  rolled  and  rounded  masses.  For  some  of  its  forms, 
however,  see  figs.  154,  155,  156,  157. 


FIG.  154. 


FIG.  155. 


FIG.  156. 


FIG.  157. 


Composition: — No.  1  is  a  sample  from  the  Brazils; 

No.  2,  from  Siberia. 

l.  2. 

Alumina  .  „  .  •  ^  .  78-10 
Glucina  .  .  *  •„..'..  .  17'94 
Iron  oxide  4*46 


78-92 

18-02 

3-12 


Chromium  oxide     .   -,  .  -9 
Copper  and  lead  oxides  , 


100-50 


036 
0-29 

10071 


YELLOW   TOPAZ. 


The  general  characteristics  of  this  stone  are  described 
under  '  White  Topaz.' 


YELLOW   TOURMALINE. 


Specific  gravity,  3'00  to  3-22  ;  hardness,  7  to  7'5.  The 
tourmaline  becomes  electrical  by  heat ;  one  portion  of  a 
crystal  attracts  light  bodies,  the  other  repels  them.  Its 


794 


GEMS   AND   PRECIOUS  STONES. 


colour   is  very  varied.     The   tourmaline  lias  a  vitreous 
fracture.     It  occurs  in  semicrystalline  prisms  of  irregular 


FIG.  158. 


FIG.  159. 


FIG.  160. 


FIG.  161. 


FIG.  162. 


FIG.  163. 


form,  generally  deeply  striated,  and  in  prisms  of  six  or 
more  sides,  variously  terminated,  one  end  usually  differing 
from  the  other. 

Figs.  158,  159,  160,  161,  162,  and  163  represent  some 
of  the  forms  of  this  mineral. 


YELLOW    EMEKALD. 


Specific  gravity,  2'73  to  2'76  ;  hardness,  7*5  to  8.     The 
emerald  occurs  of  many  colours ;  its  tint  par  excellence  is 


YELLOW   STONES 


795 


green  ;  but  there  are  many  varieties  tinged  more  or  less 
yellow  or  blue,  and  they  even  occur  white.     Its  fracture 


FIG.  165. 


FIG.  166. 


FIG.  164. 


FIG.  167. 


FIG.  168. 


FIG.  170 


FIG.  160. 


is  vitreous,  brilliant,  and  undulating.     Its  common  form 
is.  the  hexahedral  prism,  sometimes  deeply  striated  longi- 


796 


GEMS   AND    PRECIOUS   STONES. 


tudinally.  It  readily  cleaves  parallel  to  all  the  planes  of 
its  primary  form — the  hexahedral  prism. 

The  above  are  some  of  the  forms  it  assumes  :  figs.  164, 
165,  166,  167,  168,  169.,  and  170. 

Composition : — 


Glucina 
Silica 
Alumina 
Iron  oxide 


15-50 
66 '45 
1675 
•60 
99-30 


The  green  varieties  contain  a  small  quantity  of  chro- 
mium oxide. 

TABLE  II. 
COMPARATIVE  TABLE  OF  THE  WEIGHTS  or  YELLOW  STONES 

WEIGHED   IN    AlR   AND    WATER. 


Weight 

Weight  in  Water 

in  air 

Grains 

Yellow            Yellow 

Yellow 

Yellow 

Yellow 

Yellow          Yellow 

Zircon           Sapphire 

Cymophane       Topaz 

Tourmaline 

Emerald 

Quartz 

1 

0-775 

0-766 

9-738 

0-716 

0-690 

0-633 

0-611 

4 

3-10 

3-06 

2-95 

2-86 

2-76 

2-53 

2-42 

8 

6-20 

6-12 

5-90 

5-72 

5-52 

5-06 

4-86 

12 

9-30 

9-18 

8-85 

8-58 

8-28 

7-59 

7-31 

36 

12-40 

12-25 

11-80 

11-55 

11-04 

10-12 

9-75 

20 

15-50 

16-31 

14-75 

14-42 

13-80 

12-65 

12-19 

& 

18-60 

18-07 

17-70 

17-28 

16-56 

15-19 

14-04 

•28 

21-70 

21  44 

2065 

20-15 

19-32 

17-72 

17-08 

32 

24-80 

24-51 

23-60 

23-01 

20-08 

20-25 

19-53 

36 

2790 

27-57 

26-55 

25-88 

24-84 

22-77 

21-98 

40 

31-00 

30-64 

29-50 

29-75 

27-60 

25-30 

24-43 

44 

34-10 

33-71 

32-45 

31-61 

30-36 

27-83 

26-88 

48 

37-20 

36-76 

35-40 

34-47 

33-12 

30-36 

29-32 

52 

40-30 

39-82 

38-35 

37-34 

35-88 

32-89 

31-77 

56 

4340 

42-89 

41-30 

40-20 

3864 

35-43 

34-21 

60 

46-50 

45-95 

44-25 

43-06 

41-40 

37-94 

36-66 

64    ; 

49-60 

49-01 

47-20 

45-93 

44-16 

40-47 

39-11 

68 

52-70 

52-08 

50-15 

48-90 

4(5-92 

43-00 

41-56 

72 

55-80 

55-14 

53-10 

51-77 

4968 

45-53 

44-00 

76 

58-90 

58-21 

56-05 

54-63 

52-44 

48-07 

46-44 

80 

62-00 

61-28 

59-00 

57-49 

55-20 

50-60 

48-88 

84 

65-10 

64-34 

61-95 

60-35 

57-96 

53-13     i    51-32 

88    ! 

68-20 

67-41 

64-90 

63-22 

6072 

55-66 

53-76 

92    : 

71-30 

70-47 

67-85 

66-08 

63-48 

58-19 

56-21 

96  ; 

74-40 

73-54 

70-80 

68-94 

66-24 

60-72 

58-65 

100 

77-50 

76-60 

73-75 

71-80 

69-00 

63-25 

61-09 

Specific 
Gravity 

[    4-44 
' 

4-27 

3-89 

3-53 

3-22 

2-72 

2-55 

BROWN   AND    FLAME-COLOURED   STONES. 


797 


YELLOW   QUARTZ. 

"For  the  characteristics,  hardness,  &c.,  of  this  mineral, 
see  '  White  Quartz.' 

BROWN  AND  FLAME-COLOURED  STONES. 

ZIRCON  (HYACINTH). 
For  characteristics,  &c.,  see  '  White  Zircon.' 

VERMEIL  GARNET,  NOBLE  GARNET,  ALMANDINE. 

Specific  gravity,  4  to  4*2  ;  hardness,  6'5  to  7'5.     There 
are  very  many  varieties  of  garnet,  variously  coloured  ;  but 


FIG.  171. 


FIG.  172. 


their  crystalline  form — a  rhombic  dodecahedron,  more  or 
less  modified — is  a  distinguishing  characteristic.  The 
colouring  matter  of  the  garnet  is  iron.  Figs.  171, 172, 173, 
174  and  175  represent  some  of  its  crystalline  forms. 


798 


GEMS   AND    PRECIOUS   STONES. 
FIG.  174.  FIG,  175. 


Composition : — 

Silica          '. 
Alumina     ..;•      . 
Iron  oxide  . 
Manganese  oxide 


TABLE  III. 


3375 

27-25 

36-00 

•25 

97-25 


COMPARATIVE  TABLE  or  THE  WEIGHTS  OP  BROWNISH  AND  FLAME- 
COLOURED  STONES  WEIGHED  IN  AIR  AND  WATER. 


Weight  in 

Weight  in  water 

Air 

Grains 

Hyacinthine  Zircon 

Vermeil  Garnet 

Essonile 

Tourmaline 

1 

0-775 

0-750 

0-710 

0-690 

4 

3-10 

3-00 

2-87 

2-76 

8 

6-20 

6-00 

5-74 

5-52 

12 

9-30 

9-00 

8-61 

8-28 

36 

1240 

12-00 

11-48 

11-04 

20 

15-50 

15-00 

14-35 

13-80 

24 

18-60 

18-00 

17-22 

16-56 

28 

21-70 

21-00 

20-09 

19-32 

32 

24-80 

24-00 

22-96 

22-08 

36 

27-90 

27-00 

25-83 

24-84 

40 

31-30 

30-00 

28-70 

27-60 

44 

34-10 

33-00 

31-57 

30-36 

48 

37-20 

36-00 

34-44 

33-12 

62 

40-30 

39-00 

37-31 

35-88 

56 

43-40 

42-00 

40-18 

38-64 

60 

46-50 

45-00 

43-05 

4140 

64 

49-60 

48-00 

45-92 

44-16 

68 

52-70 

51-00 

48-79 

46-92 

72 

55-80 

54-00 

51-66 

49-68 

76 

58-90 

57-00 

54-53 

52-44 

80 

61-00 

60-00 

57-40 

55-20 

84 

65-10 

63-00 

60-27 

57-96 

88 

68-20 

66-00 

63-14 

60-72 

92 

71-30 

69-00 

66-01 

63-48 

96 

74-40 

72-00 

68-88 

66-24 

100 

77-50 

75-00 

71-75 

69-00 

Specific 
Gravity 

4-44 

4-00 

3-54 

3-22 

RED  AND   ROSE-COLOUEED   STONES.  799 

ESSONITE,   CINNAMON   STONE. 

Specific  gravity,  3-5  to  3-6.  This  stone  has  an  agree- 
able orange-yellow  tinge,  which  becomes  a  warm  and 
brilliant  tint  when  the  mass  is  large.  This  stone  is  not 
usually  found  crystalline,  but  in  irregular  forms  and 
masses,  which  are  characterised  by  fissures  in  all  direc- 
tions. 

Composition  : — 

Silica          .         .        .         .        ,        :        .     38-80 

Alumina 21-20 

Lime 31-25 

Iron  oxide  with  small  quantities  of  Potash  I      Q  ^ 
and  Magnesia  j 

97-75 

TOURMALINE. 

For  the  characteristics  of  this  mineral  see  '  Yellow 
Tourmaline.' 

RED  AND   ROSE-COLO  CTRED   STONES, 
RED   SAPPHIRE    (ORIENTAL   RUBY). 

For  characteristics,  crystalline  form,  &c.,  see  '  White 
Sapphire.' 

DEEP  RED  GARNET,  NOBLE  GARNET. 

For  characteristics,  &c.,  see  '  Vermeil  Garnet.' 

SPINEL  RUBY. 

Specific  gravity  3'5  to  3-6  :  hardness,  8.  The  spinel 
xeadily  scratches  quartz,  but  is  scratched  by  the  sapphire. 
Its  special  colour  is  red,  approaching  a  rose  tint:  this 
tinge,  however,  undergoes  various  modifications,  such  as 
scarlet,  red,  rose,  yellowish -red,  and  reddish-purple :  it 
is  also  found  blue  and  black.  Its  fracture  is  flattish- 
<jonchoidal,  with  a  splendent  vitreous  lustre.  It  occurs 
crystallised  in  regular  octahedrons,  sometimes  having 
their  edges  replaced  as  in  macles  :  sometimes  it  assumes 
the  globular  form.  The  spinel  may  be  distinguished  from 
the  red  sapphire  and  the  garnet  by  hardness  and  specific 


800 


•     GEMS   AXD    PRECIOUS   STONES. 


gravity  ;  and  from  reddish  topaz,  which  possesses  nearly 
the  same  specific  gravity,  by  its  electric  properties. 
Composition  of  spinel  ruby  : — 


Silica 

Alumina     . 
Magnesia    . 
Iron  protoxide     , 
Chromium  oxide 


•02 

6901 

26-21 

071 

I'll 

99-06 


REDDISH   TOPAZ. 


For  characteristics,  &c.,  see  '  White  Topaz.' 

RED   TOURMALINE. 

For  characteristics,  &c.,  see  'Yellow  Tourmaline.' 

TABLE  IV. 

COMPARATIVE  TABLE  OF  THE  WEIGHTS  OF  RED  OR  ROSE-COLOURED 
STONES  WEIGHED  IN  AIR  AND  WATER. 


Weight 

Weight  in  Water 

in  Air 

Grains 

Red  Sapphire 

Deep  Garnets 

Spinel 

Smoke  or  Red 
Topaz 

Red  Tourmaline 

1 

0-766 

0-750 

0-722 

0-716 

0-690 

4 

3-060 

3-700 

2-880 

2-860 

2-760 

8 

6-120 

6-000 

5-770 

5-720 

5-520 

12 

9180 

9-000 

8-660 

8-585 

8-280 

16 

12-250 

12-000 

11-550 

11-550 

11-040 

20 

15-310 

15-000 

14-440 

14-420 

13-800 

24 

18-370 

18-000 

17-330 

17-280 

16-560 

28 

21-440 

21-000 

20-220 

20-150 

19-320 

32 

24-510 

24-000 

23-110 

23-610 

22-080 

36 

27-570 

27-000 

26-000 

25-880 

24-840 

40 

30-640 

30-000 

28-880 

28-750 

27-600 

44 

33-710 

33-000 

31-770 

31-610 

30-360 

48 

36-760 

36-000 

34-660 

34-470 

33-120 

52 

39-820 

39-000 

37-550 

37-340 

35-880 

66 

42-890 

42-000 

40-440 

40-200 

38-640 

60 

44-950 

45-000 

43-300 

43-060 

41-400 

64 

49-010 

48-000 

46-220 

45-930 

44-160 

,  68 

52-080 

51-000 

49-110 

48-900 

46-920 

72 

55-140 

54-000 

51-990 

51-770 

49-680 

76 

58-210 

57-000 

54-880 

54-630 

52-440 

80 

61-280 

60-000 

57-770 

57-490 

52-200 

84 

64-340 

63-000 

60-660 

60-350 

57-960 

88 

-  67-410 

66-000 

63-550 

63-220 

60-720 

92 

70-470 

69-000 

66-440 

66-080 

63-480 

96 

73-540 

72-000 

69-330 

68-940 

66-240 

100 

76-600 

75-000 

72-220 

71-800 

69-000 

Specific 
Gravity 

|  .4-270 

.4-000 

3-600 

3-530 

3-220 

BLUE   STONES.  801 

BLUE   STONES. 
BLUE   SAPPHIRE. 

For  characteristics,  &c.,  see  '  White  Sapphire/ 

DISTHENE.    CYANITE. 

Specific  gravity,  3*5  to  3'7  ;  hardness,  5  to  7.  Fine 
specimens  of  disthene  possess  a  bright  blue  colour,  which 
passes  insensibly  into  a  deep  sky  blue.  Its  transparency 
is  nearly  perfect,  and  it  presents  small  pearly  reflections, 
which  add  to  the  beauty  of  its  colour.  The  primary  form 
of  its  crystals  is  a  doubly  oblique  prism,  and  they  cleave 
very  readily  in  the  direction  of  their  length.  It  can  be 

FIG.  176.  FIG.  177.  FIG.  178. 


readily  distinguished  from  the  sapphire  by  its  being  less 
hard,  as  also  by  its  specific  gravity.  Figs.  176,  177,  and 
178  represent  some  of  its  crystalline  forms. 

Composition  of  a  specimen  from  St.  Gothard  : — 

Silica .         .     43-0 

Alumina       ........     5o-0 

Iron  oxide     .         .         .         .         .         .         .         *5 

98^5 
BLUE   TOPAZ. 

For  characteristics,  &c.,  see  'White  Topaz.'  Blue 
topaz  and  disthene  having  the  same  specific  gravity,  may 
by  that  test  alone  be  confounded  with  each  other ;  but 
the  appearance  of  each  is  so  different  that  they  can 
rarely  be  confounded.  If,  however,  the  electrical  test  be 
applied,  no  fear  of  mistaking  one  for  the  other  need  be 
entertained,  as  only  the  topaz  becomes  electrical. 

3  F 


802  GEMS   Am)   PRECIOUS   STONES. 

BLUE   TOURMALINE. 

For  characteristics,  &c.,  see  '  Yellow  Tourmaline.' 

BLUE   BERYL. 

For  characteristics,  &c.,  see  '  Emerald.'  The  tint  and 
appearance  of  this  stone  and  that  of  the  blue  topaz  are 
so  similar  'that  they  cannot  be  distinguished  by  that  test ; 
their  specific  gravities,  however,  are  so  different  that  they 
may,  by  this  simple  means,  be  readily  discriminated. 

DICHROITE,   WATER   SAPPHIRE. 

Specific  gravity,  2-56  to  2-65  ;  hardness,  7  to  7'5.  The 
chief  characteristic  of  this  stone,  is  that  it  possesses  a 
double  colour  ;  that  is,  it  is  a  fine  blue  or  a  normal  yellow, 
as  it  is  viewed  in  the  direction  of  its  base,  or  the  planes 
of  a  hexahedral  prism,  which  is  its  crystalline  form.  It 
can  be  thus  readily  distinguished,  as  also  by  its  having 
nearly  the  same  specific  gravity  as  quartz,  and  thus  being 
the  lightest  of  the  blue  stones.  Composition  : — 

Silica  48-35 


Alumina      . 
Magnesia    . 
Iron  protoxide     . 
Manganese  protoxide 
Loss  in  fire  (water  ?) 


31-71 
10-16 
8-12 
•33 
•60 

99-27 
TURQUOISE. 

Specific  gravity,  2-  8  to  3  ;  hardness,  5  to  6.  This  stone 
has  not  been  placed  in  the  list  of  specific  gravities,  as  it 
can  be  so  readily  detected  by  its  appearance.  It  is  bright 
or  greenish-blue  in  colour  ;  its  aspect  is  earthy  or  compact. 
It  scratches  apatite,  and  even  glass  ;  but  is  scratched  by 
quartz.  It  occurs  filling  fissures,  or  forming  concretions 
in  siliceous  and  argillo-ferruginous  rocks.  Composition  :  — 

Phosphoric  acid  .        >      ..    "...     ^.  .  17-86 

Alumina     .         .,       .         .  '     .        .  •  .  10*01 

Silica          .         '.        '.    '     .      .  .         .  .  8'90 

Iron  peroxide      .        :        .     '  ,  ,         .  .  36'82 

Lime  .....         .  <  ..  .  0-15 

Water  and  fluoric  acid  .         .  . 


99*69 


VIOLET   STONES. 


803 


TABLE  V. 

COMPAKATTVE  TABLE  OF  THE  WEIGHTS  OF  BLUE  SlOTTES  WEIGHED 
IN  AIR  AND  WATEB. 


Weight 

Weight  in  Water 

in  Air 

Grains 

Blue 
Sapphire 

Disthene, 
Cyanite 

Bine 
Topaz 

Tourmaline 

Blue 
Beryl 

Dichroite, 
Water 
Sapphire 

1 

0-766 

0-717 

0-716 

0-690 

0633 

0-622 

4 

3-06 

2-87 

2-86 

2-16 

253 

2-49 

8 

6-12 

5-74 

5-72 

5-52 

5-06 

4-98 

12 

9-18 

8-61 

8-58 

8-28 

7-59 

7-47 

16 

12-25 

11-48 

11-45 

11-04 

10-12 

9-96 

20 

15-31 

14-35 

14-42 

13-80 

12-65 

12-45 

24 

18-37 

17-22 

17-18 

16-56 

15-19 

14-94 

28 

21-44 

20-09 

20-05 

19-32 

17-72 

17-43 

32 

24-51 

22-96 

22-91 

20-08 

20-25 

19-92 

36 

27-57 

25-83 

25-78 

24-84 

22-77 

22-41 

40 

30-64 

28-70 

28-65 

2760 

25-30 

24-90 

44 

33-71 

31-57 

31-51 

30-66 

27-83 

27-39 

48 

36-76 

34-44 

34-37 

33-12 

30-36 

29-88 

52 

39-82 

37-31 

37-24 

35-88 

32-89 

32-37 

56 

42-89 

40-18 

40-10 

38-64 

35-43 

34-86 

60 

45-95 

43-05 

42-96 

41-40 

37-94 

37-35 

64 

49-01 

45-92 

45-83 

44-16 

40-47 

39-84 

68 

52-08 

48-79 

48-80 

46-92 

43-00 

42-33 

72 

55-14 

51-66 

51-67 

49-68 

4553 

44-82 

76 

58-21 

54-53 

54-53 

52-44 

48-07 

47-31 

80 

61-28 

57-40 

57-49 

55-20 

50-60 

49-80 

84 

64-34 

60-27 

60-25 

57-96 

53-13 

52-29 

88 

67-41 

63-14 

63-12 

60-72 

55-66 

54-78 

92 

70-47 

66-01 

65-98 

63-48 

58-19 

57-27 

96 

73-54 

68-88 

63-84 

66-24 

60-72 

59-76 

100 

76-60 

71-75 

71-70 

69-00 

63-25 

62-25 

Specific 
Gravity 

1     4-27 

1 

3-54 

3-53 

3-22 

2-72 

2-65 

VIOLET   STONES. 
VIOLET   SAPPHIRE, 

For  characteristics,  &c.,  see  '  White  Sapphire/ 

VIOLET   TOURMALINE 

For  characteristics,  &c.,  see  '  Yellow  Tourmaline/ 

VIOLET   QUARTZ,   AMETHYST. 

For  characteristics,  &c.,  see  '  White  Quartz/ 

3  F  2 


804 


GEMS  AND   PRECIOUS  STONES. 


TABLE  VI. 

COMPARATIVE  TABLE  OF  THE  WEIGHTS  OF  VIOLET  STONES  WEIGHED 
IN  AIR  AND  WATER. 


Weight  in  Water 

Weight  in  Air 
Grains 

Violet  Sapphire 

Violet  Tourmaline 

Amethystine  Quartz 
(Amethyst) 

1 

0766 

0-690 

0-611 

4 

3-06 

2-76 

2-42 

8 

6-12 

5-52 

4-86 

12 

9-18 

8-28 

7-31 

16 

12-25 

11-04 

9-75 

20 

15-31 

13-80 

12-19 

24 

18-37 

16-56 

14-64 

28 

21-44 

19-32 

1708 

32 

24-51 

20-08 

19-53 

36 

27-57 

24-84 

21-98 

40 

30-64 

27-60 

24-43 

44 

33-71 

30-36 

26-88 

48 

36-76 

33-12 

29-32 

52 

39-82 

35-88 

3177 

66 

42-89 

38-64 

34-21 

60 

45-95 

41-40 

36-66 

64 

49-01 

44-16 

39-11 

68 

52-02 

46-92 

41-56 

72 

65-14 

49-68 

44-00 

76 

58-21 

62-44 

46-44 

80 

61-28 

55-20 

48-88 

84 

64-34 

57-96 

51-32 

88 

67-41 

60-72 

53-76 

92 

70-47 

63-48 

56-21 

96 

73-54 

66-24 

58-65 

100 

76-60 

69-00 

61-09 

Specific  Gravity 

4-27 

3-22 

2-55 

GREEN   STONES. 
GREEN    SAPPHIRE. 

For  characteristics,  &c.,  see  '  Yellow  Emerald.' 

PERIDOT,    CRYSOLITE. 

Specific  gravity,  3-3  to  3-5  ;  hardness,  6'5  to  7.  This 
stone  has  a  more  or  less  deep  olive  or  yellowish-green 
colour.  It  is  more  generally  found  in  rolled  grains  than 
in  regular  prismatic  crystals.  It  is  possessed  in  a  very 
high  degree  of  double  refraction.  Figs.  179,  180,  181, 
and  182  represent  some  of  its  crystalline  forms. 


GREEN   STONES. 


805 


GREEN    TOURMALINE. 

For  characteristics,  see  '  Yellow  Tourmaline/ 


EMERALD. 

For  characteristics,  see  '  Yellow  Emerald.' 

FIG.  179.  FIG.  180. 


FIG.  181. 


FIG.  182. 


AQUA-MARINE. 

This  stone  possesses  a  very  pale   green  tinge.     For 
other  characteristics,  see  '  Yellow  Emerald.' 


CHRYSOPRASE. 


This  mineral  is  a  green-coloured  quartz,  and  can  be 
readily  recognised  by  referring  to  the  characteristics  of 
quartz. 


806 


GEMS   AXD    PEECIOUS   STONES 


TABLE  VII. 

COMPAEATIVE   TABLE  OF   THE  WEIGHTS   OF   GREEN   STONES   WEIGHED 

IN  Am  AND  WATER. 


Weight 

Weight  in  Water 

in  Air 

Grains 

Green 
Sapphire 

Peridot 

Green 
Tourmaline 

Emerald 

Aqua-marine 

Chrysoprase 

1 

0-766 

0708 

0-690 

0-633 

0-633 

0-611 

4 

3-06 

2-83 

2-76 

2-53 

2-53 

2-42 

8 

6-12 

5-66 

5-52 

5-06 

5-06 

4-86 

12 

9-18 

8-49 

8-28 

7-59 

7-59 

7-31 

16 

12-25 

11-32 

11-04 

10-12 

10-12 

975 

20 

15-31 

14-16 

13-80 

12-65 

12-65 

12-19 

94 

18-37 

16-99 

16-56 

15-19 

15-19 

14-64 

28 

21-44 

19-82 

19-32 

17-72 

17-72 

17-08 

32 

24-51 

22-65 

22-08 

20-25 

20-25 

19-53 

56 

27-57 

25-48 

24-84 

22-77 

27-77 

21-98 

40 

30-64 

28-32 

27-60 

25-30 

25-30 

24-43 

44 

33-71 

31-15 

30-36 

27-83 

27-83 

36-88 

48 

36-76 

33-98 

33-12 

30-36 

30-36 

29-32 

52 

39-82 

36-81 

35-88 

32-89 

32-89 

31-77 

56 

42-89 

39-64 

38-64 

35-43 

35-43 

34-21 

60 

45-95 

42-48 

41-40 

37-94 

37-94 

36-66 

64 

49-01 

45-31 

44-16 

40-47 

40-47 

39-11 

68 

62-08 

48-14 

46-92 

43-00 

43-00 

41-56 

72 

55-14 

5097 

49-68 

45-53 

45-53 

44-00 

76 

58-21 

53-80 

52-44 

48-07 

48-07 

46-44 

80 

61-28 

56-64 

55-20 

50-60 

50-60 

48-88 

84 

64-34 

59-47 

57-96 

53-13 

53-13 

51-32 

88 

67-41 

62-30 

60-72 

55-66 

55-66 

53-76 

92 

70-47 

65-13 

63-48 

58-19 

58-19 

56-21 

96 

73-54 

67-96 

66-24 

60-72 

60-72 

58-65 

100 

76-60 

70-80 

69-00 

63-25 

63-25 

61-09 

Specific 
Gravity 

|   4-27 

3-42 

3-22 

2-72 

2-72 

2-56 

STONES   POSSESSING  A   PLAY  OF   COLOUES 
(CHATOYANT}. 

In  the  following  list  of  stones  no  regard  has  been  paid 
to  absolute  colours,  but  only  to  the  play  of  colours  the 
stones  exhibit.  This  play  or  reflection  is  of  two  kinds : 
in  some,  as  the  sapphires,  it  appears  as  a  white  star  with 
six  rays,  on  a  blue,  red,  or  yellow  ground  ;  or  on  a  purple 
ground  in  the  garnet.  In  others  it  is  but  a  point  or  mass 
of  pearly  light,  which  sometimes  appears  to  occupy  the 
whole  of  the  stone,  and  varies  according  to  the  inclination 
given  to  the  stone.  The  cymophane,  crysolite  quartz, 
Egyptian  emerald,  felspar,  and  cat's  eye  belong  to  this 
class. 


GREEN    STONES. 


807 


The  specific  gravities  of  such  stones  as  the  opal,  &c., 
have  not  been  given,  as  their  appearance  sufficiently  charac- 
terises them. 

SAPPHIRE. 

For  characteristics,  &c.,  see  '  White  Saphhire.' 

GARNET. 

For  characteristics,  &c.,  see  '  Vermeil  Garnet.' 


CYMOPHANE. 


See  '  Cymophane.' 


ANTIQUE   EMERALD. 

For  characteristics,  &c.,  see  '  Yellow  Emerald.' 

QUARTZ. 

See  '  White  Quartz.' 

FIG,  183.  FIG.  184.  FIG.  185. 


FIG.  186. 


FIG.  187. 


808 


GEMS   AND   PRECIOUS   STONES. 


FELSPAE,   NACREOUS   FELSPAR,    FISH-EYE,  &C. 

Specific  gravity,  2-3  to  2 -5 ;  hardness  4'5  to  5.  This 
species  of  felspar  has  a  lamellar  texture.  It  will  be  seen 
by  the  lowness  of  its  specific  gravity  that  it  cannot  be 
readily  confounded  with  other  stones.  In  appearance  its 
transparency  is  nebulous,  and  it  presents  pearly  white 
reflections,  which  float  about  and  vacillate  in  proportion 
as  its  position  changes.  The  foregoing  are  some  of  the 
forms  of  felspar;  see  Figs.  183, 184,185,186, 187,  and  188. 

Composition : — 

Potash        .        .  .  .         .       •".  "  .  5-26 

.     Silica          .        .  .  .'•-..  .  52-90 

Lime  .         .  •    .  '  ;.  .'-         .         .  .  25-20 

Water         .         .    ,  ,.  .         .         .  .  16-00 

Fluoric  acid         .  .  .       '.        .  .  082 

iooii" 

TABLE  VIII. 

COMPARATIVE  TABLE  OF  THE  WEIGHTS  OP  STOKES  POSSESSING  A 
PLAT  OF  COLOURS  (CHATOYANT). 


Weight 

Weight  iu  Water 

in  Air 

Grains 

Sapphires 

Garnets 

Cymophane 

Antique 
Emerald 

Quartz 

Felspar 

1 

0-766 

0-750 

0-738 

0-633 

0-611 

0-592 

4 

3-06 

3-00 

2-95 

2-53 

2-42 

2-37 

8 

6-12 

6-00 

5-90 

5-06 

4-86    ' 

4-74 

12 

9-18 

9-00 

8-85 

7-59 

7-31 

7-11 

16 

12-25 

12-00 

11-80 

10-12 

9-75 

9-47 

20 

15-31 

15-00 

14-75 

12-65 

12-19 

11-84 

24 

18-37 

18-00 

17-70 

15-19 

14-64 

14-20 

28 

21-44 

21-00 

20-65 

17-72 

17-08 

16-57 

32 

24-51 

24-00 

23-60 

20-25 

19-53 

18-94 

36 

27-57 

27-00 

26-55 

22-77 

21-98 

21-31 

40 

30-64 

30-00 

29-50 

25-30 

24-43 

23-68 

44 

33-71 

33-00 

32-46 

27-83 

26-88 

26-05 

48 

3676 

36-00 

35-40 

30-36 

29-32 

28-42 

52 

39-84 

39-00 

38-35 

32-89 

31-77 

30-79 

56 

42-89 

42-00 

41-30 

35-43 

34-21 

33-15 

60 

45-95 

45-00 

44-25 

37-94 

36-66 

35-52 

64 

49-01 

48-00 

47-20 

40-47 

39-11 

37-88 

68 

52-07 

51-00 

50-15 

43-00 

41-56 

40-25 

72 

55-14 

54-00 

53-10 

45-53 

44-00 

42-62 

76 

58-21 

57-00 

56-05 

48-07 

46-44 

44-99 

80 

61-28 

60-00 

59-00 

50-60 

48-88 

47-36 

84 

64-34 

63-00 

61-95 

53-13 

51-32 

49-73 

88 

67-47 

66-00 

64-90 

55-66 

53-76 

52-10 

92 

70-47 

69-00 

67-85 

58-19 

56-21 

54-47 

96 

73-54 

72-00 

70-80 

60-72 

58-65 

56-84 

100 

76-60 

75-00 

73-75 

63-25 

61-09 

59-21 

Specific 
Gravity 

|     4-27 

4-00 

3-89 

2-72 

2-55 

2-45 

ARTIFICIAL   GEMS.  809 


GLASS  AND  ARTIFICIAL   GEMS. 

Glass  is  often  used  to  imitate  gems,  but  can  be  easily 
distinguished  by  the  following  characters  : — 

1.  Inferior  brilliancy. — Though  in  many  cases  artificial 
gems  have  a  fine  lustre,  they  are  invariably  soft.     The 
materials  which  communicate  brilliancy  to  glass  impair 
its  hardness  ;   and  the  result  is  that   glass  gems,  when 
examined  by  a  lens,  are  generally  found  to  have  blunt  or 
jagged   corners   and   edges,   and   surfaces   covered   with 
minute,  irregular  scratches.     This  is  invariably  the  case 
after  the  glass  gem  has  been  a  little  in  use,  and  thus  the 
brilliancy  soon  becomes  impaired. 

2.  Inferior  hardness. — Artificial  gems  can  be  scratched 
with  a  knife,  using  a  slight  pressure.     Faint  scratches  are 
made  visible  by  breathing  upon  them,  whereas  true  gems 
retain  the  original  brilliancy   which   they   possessed   on 
leaving  the  lapidary's  wheel.     The  polished  faces  of  true 
gems  cannot  be  scratched  with  a  knife  ;  moreover,  after 
long  wear,  they  show  no  signs  of  scratches. 

3.  Polished  gems  become  readily  electric  by  friction, 
particularly  the  topaz  and  diamond ;  but  glass  imitations 
require  much  longer  friction  to  produce  the  same  effect, 
and  also  retain  the  electric  power  for  a  shorter  time. 

4.  Glass  is  fusible  in  the  blowpipe  flame. 


APPENDIX 


TABLE  I 


Showing  the  Quantity  of  FINE  G-OLD  in  1  oz.  of  any  ALLOY  to 
^  of  a  Carat  Grain  and  the  MINT  VALUE  of  1  oz.  of  each 
Alloy. 


FINE  GOLD, 

Per  Ounce 

CARAT  GOLD, 

Per  Ounce 

STERLING  VALUE, 

Per  Ounce 

Oz. 

Dwts 

Ors. 

Carats 

Grs. 

Eighths 

£ 

5. 

d. 

I 

0 

0:000 

24 

0 

0 

4 

4 

11-4545 

0 

19 

23-375 

23 

3 

7 

4 

4 

10-1271 

0 

19 

22-750 

23 

3 

6 

4 

4 

8-7997 

0 

19 

22-125 

23 

3 

5 

4 

4 

7-4723 

0 

19 

21-500 

23 

3 

4 

4 

4 

6-1448 

0 

19 

20-875 

23 

3 

3 

4 

4 

4-8174 

0 

19 

20-250 

23 

3 

2 

4 

4 

3-4900 

0 

19 

19-625 

23 

3 

1 

4 

4 

2-1626 

0 

19 

19-000 

23 

3 

0 

4 

4 

0-8352 

0 

19 

18-375 

23 

2 

7 

4 

3 

11-5078 

0 

19 

17-750 

23 

2 

6 

4 

3 

10-1804 

0 

19 

17-125 

23 

2 

5 

4 

3 

8-8529 

0 

19 

16-500 

23 

2 

4 

4 

3 

7-5255 

0 

19 

15-875 

23 

2 

3 

4 

3 

6-1981 

0 

19 

15-250 

23 

2 

2 

4 

3 

4-8707 

0 

19 

14-625 

23 

2 

1 

4 

3 

3-5433 

0 

19 

14-000 

23 

2 

0 

4 

3 

2-2159 

0 

19 

13-375 

23 

1 

7 

4 

3 

0-8885 

0 

19 

12-750 

23 

1 

6 

4 

2 

11-5610 

0 

19 

12-125 

23 

1 

5 

4 

2 

10-2336 

0 

19 

11-500 

23 

1 

4 

4 

2 

8-9062 

0 

19 

10-875 

23 

1 

3 

4 

2 

7-5788 

0 

19 

10-250 

23 

1 

2 

4 

2 

6-2514 

0 

19 

9-625 

23 

1 

1 

4 

2 

4-9240 

0 

19 

9-000 

23 

1 

0 

4 

2 

3-5965 

0 

19 

8-375 

23 

0 

7 

4 

2 

2-2691 

0 

19 

7-750 

23 

0 

6 

4 

2 

0-9417 

0 

19 

7-125 

23 

0 

5 

4 

1 

11-6143 

0 

19 

6-500 

23 

0 

4 

4 

1 

10-2869 

0 

19 

5-875 

23 

0 

3 

4 

1 

8-9595 

0 

19 

5-250 

23 

0 

2 

4 

1 

7-6321 

0 

19 

4-625 

23 

0 

1 

4 

1 

6-3047 

0 

19 

4-000 

23 

0 

0 

4 

1 

4-9772 

0 

19 

3-375 

22 

3 

7 

4 

1 

3-6498 

0 

19 

2-750 

22 

3 

6 

4 

1 

2-3224 

GOLD-VALUING  TABLE. 


Ill 


FINE  GOLD, 

Per  Ounce 

CARAT  GOLD, 

Per  Ounce 

STERLING  VALUE, 

Per  Ounce 

Oz. 

jfocts 

Grs. 

Carats  6 

irg.jEh 

ghths 

£ 

i 

d. 

0 

19 

2-125 

22 

3 

5 

4 

1 

0-9950 

0 

19 

1-500 

22 

3 

4 

4 

0 

11-6676 

0 

19 

0-875 

22 

3 

3 

4 

0 

10-3402 

0 

19 

0-250 

22 

3 

2 

4 

0 

8-0127 

0 

18 

23-625 

22 

3 

1 

4 

0 

7-6854 

0 

18 

23-000 

22 

3 

0 

4 

0 

6-3579 

0 

18 

22-375 

22 

2 

7 

4 

0 

4-0305 

0 

18 

21-750 

22 

2 

6 

4 

0 

3-7031 

0 

18 

21-125 

22 

2 

5 

4 

0 

2-3757 

0 

18 

20-500 

22 

2 

4 

4 

0 

0-0482 

0 

18 

19-875 

22 

2 

3 

3 

19 

11-7208 

0 

18 

19-250 

22 

2 

2 

3 

19 

10-3934 

0 

18 

18-625 

22 

2 

1 

3 

19 

8-0660 

0 

18 

18-000 

22 

2 

0 

3 

19 

7-7386 

0 

18 

17-375 

22 

1 

7 

3 

19 

6-4112 

0 

18 

16-750 

22 

1 

6 

3 

19 

4-0838 

0 

18 

16-125 

22 

1 

5 

3 

19 

3-7563 

0 

18 

15-500 

22 

1 

4 

3 

19 

2-4289 

0 

18 

14-875 

22 

1 

3 

3 

19 

0-1015 

0 

18 

14-250 

22 

1 

2 

3 

18 

11-7741 

0 

18 

13-625 

22 

1 

1 

3 

18 

10-4467 

0 

18 

13-000 

22 

1 

0 

3 

18 

8-1193 

0 

18 

12-375 

22 

0 

7 

3 

18 

7-7919 

0 

18 

11-750 

22 

0 

6 

3 

18 

6-4644 

0 

18 

11-125 

22 

0 

5 

3 

18 

4-1370 

0 

18 

10-500 

22 

0 

4 

3 

18 

3-8096 

0 

18 

9-875 

22 

0 

3 

3 

18 

2-4822 

0 

18 

9-250 

22 

0 

2 

3 

18 

0-1548 

0 

18 

8-625 

22 

0 

1 

3 

17 

11-8274 

0 

18 

8-000 

22 

0 

0 

3 

17 

10-5000 

0 

18 

7-375 

21 

3 

7 

3 

17 

8-1725 

0 

18 

6-750 

21 

3 

6 

3 

17 

7-8451 

0 

18 

6-125 

21 

3 

5 

3 

17 

6-5177 

0 

18 

5-500 

21 

3 

4 

3 

17 

4-1903 

0 

18 

4-875 

21 

3 

3 

3 

17 

3-8629 

0 

18 

4-250 

21 

3 

2 

3 

17 

2-5355 

0 

18 

3-625 

21 

3 

1 

3 

17 

0-2081 

0 

18 

3-000 

21 

3 

0 

3 

16 

11-8806 

0 

18 

2-375 

21 

2 

7 

3 

16 

10-5532 

0 

18 

1-750 

21 

2 

6 

3 

16 

8-2258 

0 

18 

1-125 

21 

2 

5 

3 

16 

7-8984 

0 

18 

0-500 

21 

2 

4 

3 

16 

6-5710 

0 

17 

23-875 

21 

2 

3 

3 

16 

4-2436 

0 

17 

23-250 

21 

2 

2 

3 

16 

3-9162 

IV 


GOLD- VALUING  TABLE. 


FINE 
Per 

GrOLD, 
Ounce 

CARAT  GOLD, 

Per  Ounce 

STERLING  VALUE, 

Per  Ounce 

Oz. 

Ihvts.    Grs. 

Carats 

Grs. 

Eighths 

£  g. 

d. 

0 

17 

22-625 

21 

2 

1 

3  16 

2-5887 

0 

17 

22-000 

21 

2 

0 

3  16 

1-2613 

0 

17 

21-375 

21 

1 

7 

3  15 

11-9339 

0 

17 

20-750 

21 

1 

6 

3  15 

10-6065 

0 

17 

20-125 

21 

1 

5 

3  15 

9-2791 

0 

17 

19-500 

21 

1 

4 

3  15 

7-9517 

0 

17 

18-875 

21 

1 

3 

3  15 

6-6243 

0 

17 

18-250 

21 

1 

2 

3  15 

5-2968 

0 

17 

17-625 

21 

1 

1 

3  15 

3-9694 

0 

17 

17-000 

21 

1 

0 

3  15 

2-6420 

0 

17 

16-375 

21 

0 

7 

3  15 

1-3146 

0 

17 

15-750 

21 

0 

6 

3  14 

11-9872 

0 

17 

15-125 

21 

0 

5 

3  14 

10-6598 

0 

17 

14-500 

21 

0 

4 

3  14 

9-3324 

0 

17 

13-875 

21 

0 

3 

3  14 

8-0049 

0 

17 

13-250 

21 

0 

2 

3  14 

6-6775 

0 

17 

12-625 

21 

0 

1 

3  14 

5-3501 

0 

17 

12-000 

21 

0 

0 

3  14 

4-0227 

0 

17 

11-375 

20 

3 

7 

3  14 

2-6953 

0 

17 

10-750 

20 

3 

6 

3  14 

1-3678 

0 

17 

10-125 

20 

3 

5 

3  14 

0-0404 

0 

17 

9-500 

20 

3 

4 

3  13 

10-7130 

0 

17 

8-875 

20 

3 

3 

3  13 

9-3856 

0 

17 

8-250 

20 

3 

2 

3  13 

8-0582 

0 

17 

7-625 

20 

3 

1 

3  13 

6-7308 

0 

17 

7-000 

20 

3 

0 

3  13 

5-4034 

0 

17 

6-375 

.  20 

2 

7 

3  13 

4-0759 

0 

17 

5-750 

20 

2 

6 

3  13 

2-7485 

0 

17 

5-125 

20 

2 

5 

3  13 

1-4211 

0 

17 

4-500 

20 

2 

4 

3  13 

0-0937 

0 

17 

3-875 

20 

2 

3 

3  12 

10-7663 

0 

17 

3-250 

20 

2 

2 

3  12 

9-4389 

0 

17 

2-625 

20 

2 

1 

3  12 

8-1115 

0 

17 

2-000 

20 

2 

0 

3  12 

6-7840 

0 

17 

1-375 

20 

1 

7 

3  12 

5-4566 

0 

17 

0-750 

20 

1 

6 

3  12 

4-1292 

0 

17 

0-125 

20 

1 

5 

3  12 

2-8018 

0 

16 

23-500 

.  20 

1 

4 

3  12 

1-4744 

0 

16 

22-875 

20 

1 

3 

3  12 

0-1470 

0 

16 

22-250 

20 

1 

2 

3  11 

10-8196 

0 

16 

21-625 

20 

1 

1 

3  11 

9-4921 

0 

16 

21-000 

20 

1 

0 

3  11 

8-1647 

0 

16 

20-375 

20 

0 

7 

3  11 

6-8373 

0 

16 

19-750 

20 

0 

6 

3  11 

5-5099 

GOLD-VALUING   TABLE. 


FINE 

Per 

GOLD, 

Ounce 

CABAT  GOLD, 

Per  Ounce 

STERLING  VALUE, 

Per  Ounce 

0*. 

Dtvts 

Grs. 

Carats  Grs. 

Eighths 

£ 

s. 

d. 

0 

16 

19-125 

20 

0 

5 

3 

11 

4-1825 

0 

16 

18-500 

20 

0 

4 

3 

11 

2-8551 

0 

16 

17-875 

20 

0 

3 

3 

11 

1-5277 

0 

16 

17-250 

20 

0 

2 

3 

11 

0-2002 

0 

16 

16-625 

20 

0 

1 

3 

10 

10-8728 

0 

16 

16-000 

20 

0 

0 

3 

10 

9-5454 

0 

16 

15-375 

19 

3 

7 

3 

10 

8-2180 

0 

16 

14-750 

19 

3 

6 

3 

10 

6-8906 

0 

16 

14-125 

19 

3 

5 

3 

10 

5-5632 

0 

16 

13-500 

19 

3 

4 

3 

10 

4-2357 

0 

16 

12-875 

19 

3 

3 

3 

10 

2-9083 

0 

16 

12-250 

19 

3 

2 

3 

10 

1-5809 

0 

16 

11-625 

19 

3 

1 

3 

10 

0-2534 

0 

16 

11-000 

19 

3 

0 

3 

9 

10-9260 

0 

16 

10-375 

19 

2 

7 

3 

9 

9-5986 

0 

16 

9-750 

19 

2 

6 

3 

9 

8-2712 

0 

16 

9-125 

19 

2 

5 

3 

9 

6-9437 

0 

16 

8-500 

19 

2 

4 

3 

9 

5-6163 

0 

16 

7-875 

19 

2 

3 

3 

9 

4-2889 

0 

16 

7-250 

19 

2 

2 

3 

9 

2-9615 

0 

16 

6-625 

19 

2 

1 

3 

9 

1-6341 

0 

16 

6-000 

19 

2 

0 

3 

9 

0-3067 

0 

16 

5-375 

19 

I 

7 

3 

8 

10-9793 

0 

16 

4-750 

19 

1 

6 

3 

8 

9-6518 

0 

16 

4-125 

19 

1 

5 

3 

8 

8-3244 

0 

16 

3-500 

19 

1 

4 

3 

8 

6-9970 

0 

16 

2-875 

19 

1 

3 

3 

8 

5-6696 

0 

16 

2-250 

19 

1 

2 

3 

8 

4-3422 

0 

16 

1-625 

19 

1 

1 

3 

8 

3-0148 

0 

16 

1-000 

19 

1 

0 

3 

8 

1-6874 

0 

16 

0-375 

19 

0 

7 

3 

8 

0-3599 

0 

15 

23-750 

19 

0 

6 

3 

7 

11-0325 

0 

15 

23-125 

19 

0 

5 

3 

7 

9-7051 

0 

15 

22-500 

19 

0 

4 

3 

7 

8-3777 

0 

15 

21-875 

19 

0 

3 

3 

7 

7-0503 

0 

15 

21-250 

19 

0 

2 

3 

7 

5-7229 

0 

15 

20-625 

19 

0 

1 

3 

7 

4-3955 

0 

15 

20-000 

19 

0 

0 

3 

7 

3-0681 

0 

15 

19-375 

18 

3 

7 

3 

7 

1-7407 

0 

15 

18-750 

18 

3 

6 

3 

7 

0-4133 

0 

15 

18-125 

18 

3 

5 

3 

6 

11-0859 

0 

15 

17-500 

18 

3 

4 

3 

6 

9-7585 

0 

15 

16-875 

18 

3 

3 

3 

6 

8-4311 

0 

15 

16-250 

18 

3 

2 

3 

6 

7-1036 

VI 


GOLD-VALUING   TABLE. 


FINE  G-OLD, 

Per  Ounce 

CARAT  GOLD, 

Per  Ounce 

STERLING  VALUE, 

Per  Ounce 

Oz. 

Drvts. 

Grs. 

Carats  Grs. 

Eighths 

£ 

s. 

d. 

0 

15 

15-625 

18 

3 

1 

3 

6 

5-7762 

0 

15 

15-000 

18 

3 

0 

3 

6 

4-4488 

0 

15 

14-375 

18 

2 

7 

3 

6 

3-1214 

0 

15 

13-750 

18 

2 

6 

3 

6 

1-7940 

0 

15 

13-125 

18 

2 

5 

3 

6 

0-4666 

0 

15 

12-500 

18 

2 

4 

3 

5 

11-1392 

0 

15 

11-875 

18 

2 

3 

3 

5 

9-8117 

0 

15 

11-250 

18 

2 

2 

3 

5 

8-4843 

0 

15 

10-625 

18 

2 

1 

3 

5 

7-1569 

0 

15 

10-000 

18 

2 

0 

3 

5 

5-8295 

0 

15 

9-375 

18 

1 

7 

3 

5 

4-5021 

0 

15 

8-750. 

18 

1 

6 

3 

5 

3-1747 

0 

15 

8-125 

18 

1 

5 

3 

5 

1-8473 

0 

15 

7-500 

18 

1 

4 

3 

5 

0-5198 

0 

15 

6-875 

18 

1 

3 

3 

4 

11-1924 

0 

15 

6-250 

18 

1 

2 

3 

4 

9-8650 

0 

15 

5-625 

18 

1 

1 

3 

4 

8-5376 

0 

15 

5-000 

18 

1 

0 

3 

4 

7-2102 

0 

15 

4-375 

18 

0 

7 

3 

4 

5-8828 

0 

15 

3-750 

18 

0 

6 

3 

4 

4-5554 

0 

15 

3-125 

18 

0 

5 

3 

4 

3-2279 

0 

15 

2-500 

18 

0 

4 

3 

4 

1-9005 

0 

15 

1-875 

18 

0 

3 

3 

4 

0-5731 

0 

15 

1-250 

18 

0 

2 

3 

3 

11-2457 

0 

15 

0-625 

18 

0 

1 

3 

3 

9-9183 

0 

15 

0-000 

18 

0 

0 

3 

3 

8-5909 

0 

14 

23-375 

17 

3 

7 

3 

3 

7-2634 

0 

14 

22-750 

17 

3 

6 

3 

3 

5-9360 

0 

14 

22-125 

17 

3 

5 

3 

3 

4-6086 

0 

14 

21-500 

17 

3 

4 

3 

3 

3-2812 

0 

14 

20-875 

17 

3 

3 

3 

3 

1-9538 

0 

14 

20-250 

17 

3 

2 

3 

3 

0-6264 

0 

14 

19-625 

17 

3 

1 

3 

2 

11-2990 

0 

14 

19-000 

17 

3 

0 

3 

2 

9-9715 

0 

14 

18-375 

17 

2 

7 

3 

2 

8-6441 

0 

14 

17-750 

17 

2 

6 

3 

2 

7-3167 

0 

14 

17-125 

17 

2 

5 

3 

2 

5-9893 

0 

14 

16-500 

17 

2 

4 

3 

2 

4-6619 

0 

14 

15-875 

17 

2 

3 

3 

2 

3-3345 

0 

14 

15-250 

17 

2 

2 

3 

2 

2-0071 

0 

14 

14-625 

17 

2 

1 

3 

2 

0-6796 

0 

14 

14-000 

17 

2 

0 

3 

1 

11-3522 

0 

14 

13-375 

17 

1 

7 

3 

1 

10-0248 

0 

14 

12-750 

17 

1 

6 

3 

1 

8-6974 

GOLD-VALUING   TABLE. 


Vll 


FINE 

GOLD, 

CARAT  GOLD, 

STERLING  VALUE, 

Per  Ounce 

Per  Ounce 

Per 

Ounce 

Oz. 

Diets. 

Grs. 

Carats 

Grs.  E 

ighth* 

£ 

t, 

d. 

0 

14 

12-125 

17 

I 

5 

3 

1 

7-3700 

0 

14 

11-500 

17 

1 

4 

3 

1 

6-0426 

0 

14 

10-875 

17 

1 

3 

3 

1 

4-7152 

0 

14 

10-250 

17 

1 

2 

3 

1 

3-3877 

0 

14 

9-625 

17 

1 

1 

3 

1 

2-0603 

0 

14 

9-000 

17 

1 

0 

3 

1 

0-7329 

0 

14 

8-375 

17 

0 

7 

3 

0 

11-4055 

0 

14 

7-750 

17 

0 

6 

3 

0 

10-0781 

0 

14 

7-125 

17 

0 

5 

3 

0 

8-7507 

0 

14 

6-500 

17 

0 

4 

3 

0 

7-4233 

0 

14 

5-875 

17 

0 

3 

3 

0 

6-0958 

0 

14 

5-250 

17 

0 

2 

3 

0 

4-7684 

0 

14 

4-625 

17 

0 

1 

3 

0 

3-4410 

0 

14 

4-000 

17 

0 

0 

3 

0 

2-1136 

0 

14 

3-375 

16 

3 

7 

3 

0 

0-7862 

0 

14 

2-750 

16 

3 

6 

2 

19 

11-4588 

0 

14 

2-125 

16 

3 

5 

2 

19 

10-1313 

0 

14 

1-500 

16 

3 

4 

2 

19 

8-8039 

0 

14 

0-875 

16 

3 

3 

2 

19 

7-4765 

0 

14 

0-250 

16 

3 

2 

2 

19 

6-1491 

0 

13 

23-625 

16 

3 

1 

2 

19 

4-8217 

0 

13 

23-000 

16 

3 

0 

2 

19 

3-4943 

0 

13 

22-375 

16 

2 

7 

2 

19 

2-1669 

0 

13 

21-750 

16 

2 

6 

2 

19 

0-8394 

0 

13 

21-125 

16 

2 

5 

2 

18 

11-5120 

0 

13 

20-500 

16 

2 

4 

2 

18 

10-1846 

0 

13 

19-875 

16 

2 

3 

2 

18 

8-8572 

0 

13 

19-250 

16 

2 

2 

2 

18 

7-5298 

0 

13 

18-625 

16 

2 

1 

2 

18 

6-2024 

0 

13 

18-000 

16 

2 

0 

2 

18 

4-8750 

0 

13 

17-375 

16 

1 

7 

2 

18 

3-5475 

0 

13 

16-750 

16 

1 

6 

2 

18 

2-2201 

0 

13 

16-125 

16 

1 

5 

2 

18 

08927 

0 

13 

15-500 

16 

1 

4 

2 

17 

11-5653 

0 

13 

14-875 

16 

1 

3 

2 

17 

10-2377 

0 

13 

14-250 

16 

1 

2 

2 

17 

8-9103 

0 

13 

13-625 

16 

1 

1 

2 

17 

7-5829 

0 

13 

13-000 

16 

1 

0 

2 

17 

6-2554 

0 

13 

12-375 

16 

0 

7 

2 

17 

4-9280 

0 

13 

11-750 

16 

0 

6 

2 

17 

3-6006 

0 

13 

11-125 

16 

0 

5 

2 

17 

2-2732 

0 

13 

10-500 

16 

0 

4 

2 

17 

0-9458 

0 

13 

9-875 

16 

0 

3 

2 

16 

11-6184 

0 

13 

9-250      16 

0 

2 

2 

16 

10-2909 

3 

G 

« 

Vlll 


GOLD-VALUING   TABLE. 


FINE  GOLD, 

Per  Ounce 

CARAT  GOLD, 

Per  Ounce 

STERLING  VALUE, 

Per  Ounce 

Oz. 

Zhvts. 

Grs. 

Carats  GTS. 

Eighths 

£ 

s. 

d. 

0 

13 

8-625 

16 

0 

1 

2 

16 

8-9635 

0 

13 

8-000 

16 

0 

0 

2 

16 

7-6363 

0 

13 

7-375 

15 

3 

7 

2 

16 

6-3089 

0 

13 

6-750 

15 

3 

6 

2 

16 

4-9815 

0 

13 

6-125 

15 

3 

5 

2 

16 

3-6541 

0 

13 

5-500 

15 

3 

4 

2 

16 

2-3267 

0 

13 

4-875 

15 

3 

3 

2 

16 

0-9992 

0 

13 

4-250 

15 

3 

2 

2 

15 

11-6718 

0 

13 

3-625 

15 

3 

1 

2 

15 

10-3444 

0 

13 

3-000 

15 

3 

0 

2 

15 

9-0170 

0 

13 

2-373 

15 

2 

7 

2 

15 

7-6896 

0 

13 

1-750 

15 

2 

6 

2 

15 

6-3622 

0 

13 

1-125 

15 

2 

5  ' 

2 

15 

5-0348 

0 

13 

0-500 

15 

2 

4 

2 

15 

3-7073 

0 

12 

23-875 

15 

2 

3 

2 

15 

2-3799 

0 

12 

23-250 

15 

2 

2 

2 

15 

1-0525 

0 

12 

22-625 

15 

2 

1 

2 

14 

11-7251 

0 

12 

22-000 

15 

2 

0 

2 

14 

10-3976 

0 

12 

21-375 

15 

1 

7 

2 

14 

9-0702 

0 

12 

20-750 

15 

1 

6 

2 

14 

7-7428 

0 

12 

20-125 

15 

1 

5 

2 

14 

6-4154 

0 

12 

19-500 

15 

1 

4 

2 

14 

5-0880 

0 

12 

18-875 

15 

1 

3 

2 

14 

3-7606 

0 

12 

18-250 

15 

1 

2 

2 

14 

2-4332 

0 

12 

17-625 

15 

1 

1 

2 

14 

1-1057 

0 

12 

17-000 

15 

1 

0 

2 

13 

11-7783 

0 

12 

16-375 

15 

0 

7 

2 

13 

10-4509 

0 

12 

15-750 

15 

0 

6 

2 

13 

9-1235 

0 

12 

15-125 

15 

0 

5 

2 

13 

7-7961 

0 

12 

14-500 

15 

0 

4 

2 

13 

6-4687 

0 

12 

13-875 

15 

0 

3 

2 

13 

5-1413 

0 

12 

13-250 

15 

0 

2 

2 

13 

3-8138 

0 

12 

12-625 

15 

0 

1 

2 

13 

2-4864 

0 

12 

12-000 

15 

0 

0 

2 

13 

1-1591 

0 

12 

11-375 

14 

3 

7 

2 

12 

11-8316 

0 

12 

10-750 

14 

3 

6 

2 

12 

10-5042 

0 

12 

10-125 

14 

3 

5 

2 

12 

9-1768 

0 

12 

9-500 

14 

3 

4 

2 

12 

7-8494 

0 

12 

8-875 

14 

3 

3 

2 

12 

6-5220 

0 

12 

8-250 

14 

3 

2 

2 

12 

5-1946 

0 

12 

7-625 

14 

3 

1 

2 

12 

3-8671 

0 

12 

7-000 

14 

3 

0 

2 

12 

2-5397 

0 

12 

6-375 

14 

2 

7 

2 

12 

1-2123 

0 

12 

5-750 

14 

2 

6 

2 

11 

11-8849 

GOLD-VALUIXG   TABLE. 


IX 


FIXE 

Per 

GOLD, 

Ounce 

CARAT  G-OLD, 

Per  Ounce 

STERLING  VALUE, 

Per  Ounce 

Oz. 

Ihvts.   Grs. 

Carats  Grs. 

Eighths 

£ 

s. 

d. 

0 

12 

5-125 

14 

2 

5 

2 

11 

10-5575 

0 

12 

4-500 

14 

2 

4 

2 

11 

9-2301 

0 

12 

3-875 

14 

2 

3 

2 

11 

7-9027 

0 

12 

3-250 

14 

2 

2 

2 

11 

6-5752 

0 

12 

2-625 

14 

2 

1 

2 

11 

5-2478 

0 

12 

2-000 

14 

2 

0 

2 

11 

3-9204 

0 

12 

1-375 

14 

I 

7 

2 

11 

2-5930 

0 

12 

0-750 

14 

1 

6 

2 

11 

1-2656 

0 

12 

0-125 

14 

1 

5 

2 

10 

11-9382 

0 

11 

23-500 

14 

1 

4 

2 

10 

10-6107 

0 

11 

22-875 

14 

1 

3 

2 

10 

9-2833 

0 

11 

22-250 

14 

1 

2 

2 

10 

7-9559 

0 

11 

21-625 

14 

1 

1 

2 

10 

6-6285 

0 

11 

21-000 

14 

1 

0 

2 

10 

5-3011 

0 

11 

20-375 

14 

0 

7 

2 

10 

3-9737 

0 

11 

19-750 

14 

0 

6 

2 

10 

2-6463 

0 

11 

19-125 

14 

0 

5 

2 

10 

1-3188 

0 

11 

18-500 

14 

0 

4 

2 

9 

11-9914 

0 

11 

17-875 

14 

0 

3 

2 

9 

10-6640 

0 

11 

17-250 

14 

0 

2 

2 

9 

9-3366 

0 

11 

16-625 

14 

0 

1 

2 

9 

8-0092 

0 

11 

16-000 

14 

0 

0 

2 

9 

6-6818 

0 

11 

15-375 

13 

3 

7 

2 

9 

5-3544 

0 

11 

14-750 

13 

3 

6 

2 

9 

4-0269 

0 

11 

14-150 

13 

3 

5 

2 

9 

2-6995 

0 

11 

13-500 

13 

3 

4 

2 

9 

1-3721 

0 

11 

12-875 

13 

3 

3 

2 

9 

0-0447 

0 

11 

12-250 

13 

3 

2 

2 

8 

10-7173 

0 

11 

11-625 

13 

3 

1 

2 

8 

9-3899 

0 

11 

11-000 

13 

3 

0 

2 

8 

8-0625 

0 

11 

10-375 

13 

2 

7 

2 

8 

6-7350 

0 

11 

9-750 

13 

2 

6 

2 

8 

5-4076 

0 

11 

9-125 

13 

2 

5 

2 

8 

4-0802 

0 

11 

8-500 

13 

2 

4 

2 

8 

2-7528 

0 

11 

7-875 

13 

2 

3 

2 

8 

1-4254 

0 

11 

7-250 

13 

2 

2 

2 

8 

0-0980 

0 

11 

6-625 

13 

2 

1 

2 

7 

10-7705 

0 

11 

6-000 

13 

2 

0 

2 

7 

9-4431 

0 

11 

5-375 

13 

1 

7 

2 

7 

8-1157 

0 

11 

4-750 

13 

1 

6 

2 

7 

6-7883 

0 

11 

4-125 

13 

1 

5 

2 

7 

5-4609 

0 

11 

3-500 

13 

1 

4 

2 

7 

4-1335 

0 

11 

2-875 

13 

1 

3 

2 

7 

2-8061 

0 

11 

2-250 

13 

1 

2 

2 

7 

1-4786 

3  G  2 


X 


GOLD-VALUING   TABLE. 


FINE 

GOLD, 

CARAT 

GOLD, 

STERLING  VALUE, 

Per  Ounce 

Per  Ounce 

Per 

Ounce 

O:. 

Dn-ts 

.   Grs. 

Carats  Grs. 

Eighths 

l 

s. 

d. 

0 

11 

1-625 

13 

1 

1 

2 

7 

0-1512 

0 

11 

1-000 

13 

1 

0 

2 

6 

10-8238 

0 

11 

0-375 

13 

0 

7 

2 

6 

9-4964 

0 

10 

23-750 

13 

0 

6 

2 

6 

8-1698 

0 

10 

23-125 

13 

0 

5 

2 

6 

6-8416 

0 

10 

22-500 

13 

0 

4 

2 

6 

5-5142 

0 

10 

21-875 

13 

0 

3 

2 

6 

4-1867 

0 

10 

21-250 

13 

0 

2 

2 

6 

2-8593 

0 

10 

20-625 

13 

0 

1 

2 

6 

1-5319 

0 

10 

20-000 

13 

0 

0 

2 

6 

0-2045 

0 

10 

19-375 

12 

3 

7 

2 

5 

10-8771 

0 

10 

18-750 

12 

3 

6 

2 

5 

9-5497 

0 

10 

18-125 

12 

3 

5 

2 

5 

8-2223 

0 

10 

17-500 

12 

3 

4 

2 

5 

6-8948 

0 

10 

16-875 

12 

3 

3 

2 

5 

5-5674 

0 

10 

16-250 

12 

3 

2 

2 

5 

4-2400 

0 

10 

15-625 

12 

3 

1 

2 

5 

2-9126 

0 

10 

15-000 

12 

3 

0 

2 

5 

1-5852 

0 

10 

14-375 

12 

2 

7 

2 

5 

0-2578 

0 

10 

13-750 

12 

2 

6 

2 

4 

10-9303 

0 

10 

13-125 

12 

2 

5 

2 

4 

9-6029 

0 

10 

12-500 

12 

2 

4 

2 

4 

8-2755 

0 

10 

11-875 

12 

2 

3 

2 

4 

6-9481 

0 

10 

11-250 

12 

2 

2 

2 

4 

5-6207 

0 

10 

10-625 

12 

2 

1 

2 

4 

4-2933 

0 

10 

10-000 

12 

2 

0 

2 

4 

2-9659 

0 

10 

9-375 

12 

1 

7 

2 

4 

1-6384 

0 

10 

8-750 

12 

1 

6 

2 

4 

0-3110 

0 

10 

8-125 

12 

1 

5 

2 

3 

10-8366 

0 

10 

7-500 

12 

1 

4 

2 

3 

9-6562 

0 

10 

6-875 

12 

1 

3 

2 

3 

8-3288 

0 

10 

6-250 

12 

1 

2 

2 

3 

7-0014 

0 

10 

5-625 

12 

1 

1 

2 

3 

5-6740 

0 

10 

5-000 

12 

1 

0 

2 

3 

4-3465 

0 

10 

4-375 

12 

0 

7 

2 

3 

3-0191 

0 

10 

3-750 

12 

0 

6 

2 

3 

1-6917 

0 

10 

3-125 

12 

0 

5 

2 

3 

0-3643 

0 

10 

2-500 

12 

0 

4 

2 

2 

11-0369 

0 

10 

1-875 

12 

0 

3 

2 

2 

9-7095 

0 

10 

1-250 

12 

0 

2 

2 

2 

8-3821 

0 

10 

0-625 

12 

0 

1 

2 

2 

7-0546 

0 

10 

0-000 

12 

0 

0 

2 

2 

5-7272 

0 

9 

23-375 

11 

3 

7 

2 

2 

4-3998 

0 

9 

22-750 

11 

3 

6 

2 

2 

3-0724 

GOLD-VALUING   TABLE. 


XI 


FINE 
Per 

GOLD, 

Ounce 

CARAT  GOLD, 

Per  Ounce 

STERLING  VALUE, 

Per  Ounce 

08. 

Itets.   Grs. 

Carats 

Grs. 

Eighths 

£   s. 

d. 

0 

9 

22-125 

11 

3 

5 

2  2 

1-7450 

0 

9 

21-500 

11 

3 

4 

2  2 

0-4176 

0 

9 

21-875 

11 

3 

3 

2  1 

11-0901 

0 

9 

20-250 

11 

3 

2 

2  1 

9-7627 

0 

9 

19-625 

11 

3 

1 

2  1 

8-4353 

0 

9 

19-000 

11 

3 

0 

2  1 

7-1079 

0 

9 

18-375 

11 

2 

7 

2  1 

5-7805 

0 

9 

17-750 

11 

2 

6 

2  1 

4-4531 

0 

9 

17-125 

11 

2 

5 

2  1 

3-1257 

0 

9 

16-500 

11 

2 

4 

2  I 

1-7982 

0 

9 

15-875 

11 

2 

3 

2  I 

0-4708 

0 

9 

15-250 

11 

2 

2 

2  0 

11-1434 

0 

9 

14-625 

11 

2 

1 

2  0 

9-8160 

0 

9 

14-000 

11 

2 

0 

2  0 

8-4886 

0 

9 

13-375 

11 

I 

7 

2  ® 

7-1612 

0 

9 

12-750 

11 

I 

6 

2  0 

5-8338 

0 

9 

12-125 

11 

I 

5 

2  0 

4-5063 

0 

9 

11-500 

11 

1 

4 

2  0 

3^1789 

0 

9 

10-875 

11 

1 

3 

2  0 

1-8515 

0 

9 

10-250 

11 

1 

2 

2  0 

0-5241 

0 

9 

9-625 

11 

1 

1 

I  19 

11-1967 

0 

9 

9-000 

11 

1 

0 

1  19 

9-8693 

0 

9 

8-375 

11 

0 

7 

1  19 

8-5419 

0 

9 

7-750 

11 

0 

6 

I  19 

7-2144 

0 

9 

7-125 

11 

0 

5 

'  I  19 

5-8870 

0 

9 

6-500 

11 

0 

4 

1  W 

4-5596 

0 

9 

5-875 

11 

0 

3 

I  19 

3-2322 

0 

9 

5-250 

11 

0 

2 

1  19 

1-9048 

0 

9 

4-625 

11 

0 

1 

1  19 

0-5774 

0 

9 

4-000 

11 

0 

0 

1  18 

11-2500 

0 

9 

3-375 

10 

3 

7 

1  18 

9-9225 

0 

9 

2-750 

10 

3 

6 

1  18 

8-5951 

0 

9 

2-125 

10 

3 

5 

1  18 

7-2677 

0 

9 

1-500 

10 

3 

4 

1  18 

5-9403 

0 

9 

0-875 

10 

3 

3 

1  18 

4-6129 

0 

9 

0-250 

10 

3 

2 

1  18 

3-2855 

0 

8 

23-625 

10 

3 

1 

1  18 

1-9580 

0 

8 

23-000 

10 

3 

0 

1  18 

0-6306 

0 

8 

22-375 

10 

2 

7 

1  17 

11-3032 

0 

8 

21-750 

10 

2 

6 

1  17 

9-9758 

0 

8 

21-125 

10 

2 

5 

1  17 

8-6484 

0 

8 

20-500 

10 

2 

4 

1  17 

7-3210 

0 

8 

19-875 

10 

2 

3 

1  17 

5-9936 

0 

8 

19-250 

10 

2 

2 

1  17 

4-6661 

Xll 


GOLD-VALUING   TABLE. 


FINE  GOLD, 

Per  Ounce 

CARAT  GOLD, 

Per  Ounce 

STERLING  VALUE, 

Per  Ounce 

0*. 

Ittvts 

.   Grs. 

Carats 

Grs. 

Eighths 

£ 

8. 

d. 

0 

6 

18-625 

10 

2 

1 

I 

17 

3-3387 

0 

8 

18-000 

10 

2 

0 

1 

17 

2-0113 

0 

8 

17-375 

10 

1 

7 

1 

17 

0-6839 

0 

8 

16-750 

10 

1 

6 

1 

16 

11-3565 

0 

8 

16-125 

10 

1 

5 

1 

16 

10-0291 

0 

8 

15-500 

10 

1 

4 

1 

16 

8-7017 

0 

8 

14-875 

10 

1 

3 

1 

16 

7-3742 

0 

8 

14-250 

10 

1 

2 

1 

16 

6-0468 

0 

8 

13-625 

10 

1 

1 

1 

16 

4-7194 

0 

8 

13-000 

10 

1 

0 

1 

16 

3-3920 

0 

8 

12-375 

10 

0 

7 

1 

16 

2-0646 

0 

8 

11-750 

10 

0 

6 

1 

16 

0-7372 

0 

8 

11-125 

10 

0 

5 

1 

15 

11-4098 

0 

8 

10-500 

10 

0 

4 

1 

15 

10-0823 

0 

8 

9-875 

10 

0 

3 

1 

15 

8-7549 

0 

8 

9-250 

10 

0 

2 

1 

15 

7-4275 

0 

8 

8-625 

10 

0 

1 

1 

15 

6-1001 

0 

8 

8-000 

10 

0 

0 

1 

15 

4-7728 

0 

8 

7-375 

9 

3 

7 

1 

15 

3-4454 

0 

8 

6-750 

9 

3 

6 

1 

15 

2-1179 

0 

:8 

6-125 

9 

3 

5 

1 

15 

0-7905 

0 

e 

5-500 

9 

3 

4 

1 

14 

11-4631 

0 

8 

4-875 

9 

3 

3 

1 

14 

10-1357 

0 

8 

4-250 

9 

3 

2 

1 

14 

8-8083 

0 

8 

3-625 

9 

3 

1 

1 

14 

7-4809 

0 

8 

3-000 

9 

3 

0 

1 

14 

6-1535 

0 

8 

2-375 

9 

2 

7 

1 

14 

4-8260 

0 

8 

1-750 

9 

2 

6 

1 

14 

3-4986 

0 

8 

1-125 

9 

2 

5 

1 

14 

2-1712 

0 

8 

0-500 

9 

2 

4 

1 

14 

0-8438 

0 

7 

23-875 

9 

2 

3 

1 

13 

11-5164 

0 

7 

23-250 

9 

2 

2 

1 

13 

10-1890 

0 

7 

22-625 

9 

2 

1 

1 

13 

8-8616 

0 

7 

22-000 

9 

2 

0 

1 

13 

7-5341 

0 

7 

21-375 

9 

1 

7 

1 

13 

6-2067 

0 

7 

20-750 

9 

1 

6 

1 

13 

4-8793 

0 

7 

20-125 

9 

1 

5 

1 

13 

3-5519 

0 

7 

19-500 

9 

1 

4 

1 

13 

2-2245 

0 

7 

19-875 

9 

1 

3 

1 

13 

0-8971 

0 

7 

18-250 

9 

1 

2 

1 

12 

11-5697 

0 

7 

17-625 

9 

1 

1 

1 

12 

10-2422 

0 

7 

17-000 

9 

1 

0 

1 

12 

8-9168 

0 

7 

16-375 

9 

0 

7 

1 

12 

7-5874 

0 

7 

15-750 

9 

0 

6 

1 

12 

6-2600 

GOLD-VALUING   TABLE. 


Xlll 


FIXE 

Per 

GOLD, 

Ounce 

CARAT  GOLD, 

Per  Ounce 

STERLING  VALUE, 

Per  Ounce 

Oz. 

Ihrt*.   Grg. 

Carats 

Grs. 

Eightlts 

£ 

8. 

d. 

0 

7 

15-125 

9 

0 

5 

I 

12 

4-9326 

0 

7 

14-500 

9 

0 

4 

I 

12 

3-6052 

0 

7 

13-875 

9 

0 

3 

1 

12 

2-2778 

0 

7 

13-250 

9 

0 

2 

1 

12 

0-9503 

0 

7 

12-625 

9 

0 

1 

1 

11 

11-6229 

0 

7 

12-000 

9 

0 

0 

1 

11 

10-2954 

0 

7 

11-375 

8 

3 

7 

1 

11 

8-9680 

0 

7 

10-750 

8 

3 

6 

1 

11 

7-6406 

0 

7 

10-125 

8 

3 

5 

1 

11 

6-3132 

0 

7 

9-500 

8 

3 

4 

1 

11 

4-9857 

0 

7 

8-875 

8 

3 

3 

1 

11 

3*6583 

0 

7 

8-250 

8 

3 

2 

1 

11 

2-3309 

0 

7 

7-625 

8 

3 

1 

1 

11 

1-0035 

0 

7 

7-000 

8 

3 

0 

1 

10 

11-6761 

0 

7 

6-375 

8 

2 

7 

1 

10 

10-3487 

0 

7 

5-750 

8 

2 

6 

1 

10 

9-0213 

0 

7 

5-125 

8 

2 

5 

1 

10 

7-6938 

0 

7 

4-500 

8 

2 

4 

1 

10 

6-3664 

0 

7 

3-875 

8 

2 

3 

1 

10 

5-0390 

0 

7 

3-250 

8 

2 

2 

1 

10 

3-7116 

0 

7 

2-625 

8 

2 

1 

1 

10 

2-3843 

0 

7 

2-000 

8 

2 

0 

1 

10 

1-0568 

0 

7 

1-375 

8 

1 

7 

1 

9 

11-7294 

0 

7 

0-750 

8 

1 

6 

1 

9 

10-4019 

0 

7 

0-125 

8 

1 

5 

1 

9 

9-0745 

0 

6 

23-500 

8 

1 

4 

1 

9 

7-7471 

0 

6 

22-875 

8 

1 

3 

1 

9 

6-4197 

0 

6 

22-250 

8 

1 

2 

1 

9 

5-0923 

0 

6 

21-625 

8 

1 

1 

1 

9 

3-7649 

0 

6 

21-000 

8 

1 

0 

1 

9 

2-4375 

0 

6 

20-375 

8 

0 

7 

1 

9 

1-1100 

0 

6 

19-750 

8 

0 

6 

1 

8 

11-7826 

0 

6 

19-125 

8 

0 

5 

1 

8 

10-4552 

0 

6 

18-500 

8 

0 

4 

1 

8 

9-1278 

0 

6 

17-875 

8 

0 

3 

1 

8 

7-8004 

0 

6 

17-250 

8 

0 

2 

1 

8 

6-4730 

0 

6 

16-625 

.8 

0 

1 

1 

8 

5-1455 

0 

6 

16-000 

8 

0 

0 

1 

8 

3-8181 

0 

6 

15-375 

7 

3 

7 

1 

8 

2-4907 

0 

6 

14-750 

7 

3 

6 

1 

8 

1-1633 

0 

6 

14-125 

7 

3 

5 

1 

7 

11-8359 

0 

6 

13-500 

7 

3 

4 

1 

7 

10-5085 

0 

6 

12-875 

7 

3 

3 

1 

7 

9-1811 

0 

6 

12-250 

7 

3 

2 

1 

7 

7-8536 

XIV 


GOLD-VALUING    TABLE. 


FINE  GOLD, 

Per  Ounce 

CARAT  GOLD, 

Per  Ounce 

STERLING  VALUE, 

Per  Ounce 

Oz. 

Dwts 

Grs. 

Carats 

Gr». 

Eighths 

£ 

s. 

d. 

0 

6 

11-625 

7 

3 

1 

I 

7 

6-5262 

0 

6 

11-000 

7 

3 

0 

1 

7 

5-1988 

0 

6 

10-375 

7 

2 

7 

1 

7 

3-8714 

0 

6 

9-750 

7 

2 

6 

1 

7 

2-5440 

0 

6 

9-125 

7 

2 

5 

1 

7 

1-2166 

0 

6 

8-500 

7 

2 

4 

1 

6 

11-8892 

0 

6 

7-875 

7 

2 

3 

1 

6 

10-5617 

0 

6 

7-250 

7 

2 

2 

1 

6 

9-2343 

0 

6 

6-625 

7 

2 

1 

1 

6 

7-8069 

0 

6 

6-000 

7 

2 

0 

1 

6 

6-5795 

0 

6 

5-375 

7 

1 

7 

1 

6 

5-2521 

0 

6 

4-750 

7 

1 

6 

1 

6 

3-9247 

0 

6 

4-125 

7 

1 

5 

1 

6 

2-5973 

0 

6 

3-500 

7 

1 

4 

1 

6 

1-2698 

0 

6 

2-875 

7 

1 

3 

1 

5 

11-9424 

0 

6 

2-250 

7 

1 

2 

1 

5 

10-6150 

0 

6 

1-625 

7 

1 

1 

1 

5 

9-2876 

0 

6 

1-000 

7 

1 

0 

1 

5 

7-9602 

0 

6 

0-375 

7 

0 

7 

1 

5 

6-6328 

0 

5 

23-750 

7 

0 

6 

1 

5 

5-3054 

0 

5 

23-125 

7 

0 

5 

1 

5 

3-9779 

0 

5 

22-500 

7 

0 

4 

1 

5 

2-6505 

0 

5 

21-875 

7 

0 

3 

1 

5 

1-3231 

0 

5 

21-250 

7 

0 

2 

i 

X 

4 

11-9957 

0 

5 

20-625 

7 

0 

1 

1 

4 

10-6683 

0 

5 

20-000 

7 

0 

0 

1 

4 

9-3409 

0 

5 

19-375 

6 

3 

7 

1 

4 

8-0134 

0 

5 

18-750 

6 

3 

6 

1 

4 

6-6860 

0 

5 

18-125 

6 

3 

5 

1 

4 

5-3586 

0 

5 

17-500 

6 

3 

4 

1 

4 

4-0312 

0 

5 

16-875 

6 

3 

3 

1 

4 

2-7038 

0 

5 

16-250 

6 

3 

2 

1 

4 

1-3764 

0 

5 

15-625 

6 

3 

1 

1 

4 

0-0490 

0 

5 

15-000 

6 

3 

0 

1 

3 

10-7216 

0 

5 

14-375 

6 

2 

7 

1 

3 

9-3941 

0 

5 

13-750 

6 

2 

6 

1 

3 

8-0667 

0 

5 

13-125 

6 

2 

5 

1 

3 

6-7393 

0 

5 

12-500 

6 

2 

4 

1 

3 

5-4119 

0 

5 

11-875 

6 

2 

3 

A 

3 

4-0845 

0 

5 

11-250 

6 

2 

2 

1 

3 

2-7571 

0 

5 

10-625 

6 

2 

1      1 

3 

1-4297 

0 

5 

10-000 

6 

2 

0 

1 

3 

0-1022 

0 

5 

9-375 

6 

1 

7 

1 

2 

10-7748 

0 

5 

8-750 

6 

1 

6 

1 

2 

9-4474 

GOLD-VALUING   TABLE. 


XV 


FIXE 

Per 

GOLD, 

Ounce 

CARAT  GOLD, 

Per  Ounce 

STERLING  VALUE, 

Per  Ounce 

Oz. 

Zhctg.       Grs. 

Carats  Grg. 

Eighths 

£ 

#.. 

d. 

0 

5 

8-125 

6 

1 

5 

1 

2 

8-1200 

0 

5 

7-500 

6 

1 

4 

1 

2 

6-7926 

0 

5 

6-875 

6 

1 

3 

1 

2 

5-4652 

0 

5 

6-250 

6 

1 

2 

1 

2 

4-1377 

0 

5 

5-625 

6 

1 

1 

1 

2 

2-8103 

0 

5 

5-000 

6 

1 

0 

1 

2 

1-4829 

0 

5 

4-375 

6 

0 

7 

1 

2 

0-1555 

0 

5 

3-750 

6 

0 

6 

1 

1 

10-8281 

0 

5 

3-125 

6 

0 

5 

1 

1 

9-5007 

0 

5 

2-500 

6 

0 

4 

1 

1 

8-1733 

0 

5 

1-875 

6 

0 

3 

1 

6-8458 

0 

5 

1-250 

6 

0 

2 

1 

5-5184 

0 

5 

0-625 

6 

0 

1 

1 

4-1910 

0 

5 

o-ooo 

6 

0 

0 

1 

2-8636 

0 

4 

23-375 

5 

3 

7 

1 

1-5362 

0 

4 

22-750 

5 

3 

6 

1 

0-2088 

0 

4 

22-125 

5 

3 

5 

1 

0 

10-8813 

0 

4 

21-500 

5 

3 

4 

1 

0 

9-5539 

0 

4 

20-875 

5 

3 

3 

1 

0 

8-2265 

0 

4 

20-250 

5 

3 

2 

1 

0 

6-8991 

0 

4 

19-625 

5 

3 

1 

1 

0 

5-5717 

0 

4 

19-000 

5 

3 

0 

1 

0 

4-2443 

0 

4 

18-375 

5 

2 

7 

1 

0 

2-9169 

0 

4 

17-750 

5 

2 

6 

1 

0 

1-5894 

0 

4 

17-125 

5 

2 

5 

1 

0 

0-2620 

0 

4 

16-500 

5 

2 

4 

0 

19 

10-9346 

0 

4 

15-875 

5 

2 

3 

0 

19 

9-6072 

0 

4 

15-250 

5 

2 

2 

0 

19 

8-2798 

0 

4 

14-625 

5 

2 

1 

0 

19 

6-9524 

0 

4 

14-000 

5 

2 

0 

0 

19 

5-6250 

0 

4 

13-375 

5 

1 

7 

0 

19 

4-2975 

0 

4 

12-750 

5 

1 

6 

0 

19 

2-9701 

0 

4 

12-125 

5 

1 

5 

0 

19 

1-6427 

0 

4 

11-500 

5 

1 

4 

0 

19 

0-3153 

0 

4 

10-875 

5 

1 

3 

0 

18 

10-9879 

0 

4 

10-250 

5 

1 

2 

0 

18 

9-6605 

0 

4 

9-625 

5 

1 

1 

0 

18 

8-3331 

0 

4 

9-000 

5 

1 

0 

0 

18 

7-0056 

0 

4 

8-375 

5 

0 

7 

0 

18 

5-6782 

0 

4 

7-750 

5 

0 

6 

0 

18 

4-3508 

0 

4 

7-125 

5 

0 

5 

0 

18 

3-0234 

0 

4 

6-500 

5 

0 

4 

0 

18 

1-6960 

0 

4 

5-875 

5 

0 

3 

0 

18 

0-3686 

0 

4 

5-250 

5 

0 

2 

0 

17 

11-0411 

XVI 


GOLD-VALUIXG   TABLE. 


FINE 

Per 

G-OLD, 

Ounce 

CARAT  GOLD, 

Per  Ounce 

STERLING  VALUE, 

Per  Ounca 

Oz. 

2>rvts.   Grs. 

Carats 

Grs. 

Eighths 

£  s. 

d. 

0 

4 

4-625 

5 

0 

1 

0  17 

9-7137 

0 

4 

4-000 

5 

0 

0 

0  17 

8-3863 

0 

4 

3-375 

4 

3 

7 

0  17 

7-0589 

0 

4 

2-750 

4 

3 

6 

0  17 

5-7315 

0 

4 

2-125 

4 

3 

5 

0  17 

4-4041 

0 

4 

1-500 

4 

3 

4 

0  17 

3-0767 

0 

4 

0-875 

4 

3 

3 

0  17 

1-7492 

0 

4 

0-250 

4 

3 

2 

0  17 

0-4218 

0 

3 

23-625 

4 

3 

1 

0  16 

11-0944 

0 

3 

23-000 

4 

3 

0 

0  16 

9-7670 

0 

3 

22-375 

4 

2 

7 

0  16 

8-4396 

0 

3 

21-750 

4 

2 

6 

0  16 

7-1122 

0 

3 

21-125 

4 

2 

5 

0  16 

5-7848 

0 

3 

20-500 

4 

2 

4 

0  16 

4-4573 

0 

3 

19-875 

4 

2 

3 

0  16 

3-1299 

0 

3 

19-250 

4 

2 

2 

0  16 

1-8025 

0 

3 

18-625 

4 

2 

1 

0  16 

0-4751 

0 

3 

18-000 

4 

2 

0 

0  15 

11-1477 

0 

3 

17-375 

4 

1 

7 

0  15 

9-8203 

0 

3 

16-750 

4 

1 

6 

0  15 

8-4929 

0 

3 

16-125 

4 

1 

5 

0  15 

7-1655 

0 

3 

15-500 

4 

1 

4 

0  15 

5-8380 

0 

3 

14-875 

4 

1 

3 

0  15 

4-5106 

0 

3 

14-250 

4 

1 

2 

0  15 

3-1832 

0 

3 

13-625 

4 

1 

1 

0  15 

1-8558 

0 

3 

13-000 

4 

1 

0 

0  15 

0-5284 

0 

3 

12-375 

4 

0 

7 

0  14 

11-2009 

0 

3 

11-750 

4 

0 

6 

0  14 

9-8735 

0 

3 

11-125 

4 

0 

5 

0  14 

8-5461 

0 

3 

10-500 

4 

0 

4 

0  14 

7-2187 

0 

3 

9-875 

4 

0 

3 

0  14 

5-8913 

0 

3 

9-250 

4 

0 

2 

0  14 

4-5639 

0 

3 

8-625 

4 

0 

1 

0  14 

3-2365 

0 

3 

8-000 

4 

0 

0 

0  14 

1-9090 

0 

3 

7-375 

3 

3 

7 

0  14 

0-5816 

0 

3 

6-750 

3 

3 

6 

0  13 

11-2542 

0 

3 

6-125 

3 

3 

5 

0  13 

9-9268 

0 

3 

5-500 

3 

3 

4 

0  13 

8-5994 

0 

3 

4-875 

3 

3 

3 

0  13 

7-2720 

0 

3 

4-250 

3 

3 

2 

0  13 

5-9446 

0 

3 

3-625 

3 

3 

1 

0  13 

4-6171 

0 

3 

3-000 

3 

3 

0 

0  13 

3-2897 

0 

3 

2-375 

3 

2 

7 

0  13 

1-9623 

0 

3 

1-750 

3 

2 

6 

0  13 

0-6349 

GOLD-VALUING   TABLE. 


XVll 


FINE  GOLD, 

Per  Ounce 

CARAT  GOLD, 

Per  Ounce 

STERLING  VALUE, 

Per  Ounce 

Oz. 

Dwts. 

£rs. 

Carats 

£r* 

Eighths 

£ 

s. 

d. 

0 

3 

1-125 

3 

2 

rt 

0 

12 

11-3075 

0 

3 

0-500 

3 

2 

4 

0 

12 

9-9801 

0 

2 

23-875 

3 

2 

3 

0 

12 

8-6527 

0 

2 

23-250 

3 

2 

2 

0 

12 

7-3250 

0 

2 

22-625 

3 

2 

1 

0 

12 

5-9978 

0 

2 

22-000 

3 

2 

0 

0 

12 

4-6704 

0 

2 

21-375 

3 

1 

7 

0 

12 

3-3430 

0 

2 

20-750 

3 

1 

6 

0 

12 

2-0156 

0 

2 

20-125 

3 

1 

5 

0 

12 

0-6882 

0 

2 

19-500 

3 

1 

4 

0 

11 

11-3607 

0 

2 

18-875 

3 

1 

3 

0 

11 

10-0333 

0 

2 

18-250 

3 

1 

2 

0 

11 

8-7059 

0 

2 

17-625 

3 

1 

1 

0 

11 

7-3785 

0 

2 

17-000 

3 

1 

0 

0 

11 

6-0511 

0 

2 

16-375 

3 

0 

7 

0 

11 

4-7237 

0 

2 

15-750 

3 

0 

6 

0 

11 

3-3963 

0 

2 

15-125 

3 

0 

5 

0 

11 

2-0688 

0 

2 

14-500 

3 

0 

4 

0 

11 

0-7414 

0 

2 

13-875 

3 

0 

3 

0 

10 

11-4140 

0 

2 

13-250 

3 

0 

2 

0 

10 

10-0866 

0 

2 

12-625 

3 

0 

1 

0 

10 

8-7592 

0 

2 

12-000 

3 

0 

0 

0 

10 

7-4318 

0 

2 

11-375 

2 

3 

7 

0 

10 

6-1044 

0 

2 

"0-750 

2 

3 

6 

0 

10 

4-7769 

0 

2 

10-125 

2 

3 

5 

0 

10 

3-4495 

0 

2 

9-500 

2 

3 

4 

0 

10 

2-1221 

0 

2 

8-875 

2 

3 

3 

0 

10 

0-7947 

0 

2 

8-250 

2 

3 

2 

0 

9 

11-4673 

0 

2 

7-625 

2 

3 

1 

0 

9 

10-1399 

0 

2 

7-000 

2 

3 

0 

0 

9 

8-8125 

0 

2 

6-375 

2 

2 

7 

0 

9 

7-4850 

0 

2 

5-750 

2 

2 

6 

0 

9 

6-1576 

0 

2 

5-125 

2 

2 

5 

0 

9 

4-8302 

0 

2 

4-500 

2 

2 

4 

0 

9 

3-5028 

0 

2 

3-875 

2 

2 

3 

0 

9 

2-1754 

0 

2 

3-250 

2 

2 

2 

0 

9 

0-8480 

0 

2 

2-625 

2 

2 

1 

0 

8 

11-5205 

0 

2 

2-000 

2 

2 

0 

0 

8 

10-1931 

0 

2 

1-375 

2 

1 

7 

0 

8 

8-8657 

0 

2 

0-750 

2 

1 

6 

0 

8 

7-5383 

0 

2 

0-125 

2 

1 

5 

0 

8 

6-2109 

0 

1 

23-500 

2 

1 

4 

0 

8 

4-8835 

0 

1 

22-875 

2 

1 

3 

0 

8 

3-5561 

0 

1 

22-250 

2 

1 

2 

0 

8 

2-2286 

XVU1 


GOLD- VALUING   TABLE. 


FINE  GOLD, 

Per  Ounce 

CARAT  GOLD, 

Per  Ounce 

STERLING  VALUE, 

Per  Ounce 

Oz. 

Dwts. 

Grs. 

Carats 

Grs. 

FAghths 

I 

*. 

d. 

0 

1 

21-625 

2 

1 

1 

0 

8 

0-9012 

0 

1 

21-000 

2 

1 

0 

0 

7 

11-5738 

0 

1 

20-375 

2 

0 

7 

0 

7 

10-2464 

0 

1 

19-750 

2 

0 

6 

0 

7 

8-9190 

0 

1 

19-125 

2 

0 

5 

0 

7 

7-5916 

0 

18-500 

2 

0 

4 

0 

7 

6-2642 

0 

17-875 

2 

0 

3 

0 

7 

4-9367 

0 

17-250 

2 

0 

2 

0 

7 

3-6093 

0 

16-625 

2 

0 

1 

0 

7 

2-2819 

0 

16-000 

2 

0 

0 

0 

7 

0-9545 

0 

15-375 

1 

3 

7 

0 

6 

11-6271 

0 

14-750 

1 

3 

6 

0 

6 

10-2997 

0 

14-125 

1 

3 

5 

0 

6 

8-9723 

0 

1 

13-500 

3 

4 

0 

6 

7-6448 

0 

1 

12-875 

3 

3 

0 

6 

6-3174 

0 

1 

12-250 

3 

2 

0 

6 

4-9900 

0 

1 

11-625 

3 

1 

0 

6 

3-6626 

0 

1 

n-ooo 

3 

0 

0 

6 

2-3352 

0 

1 

10-375 

2 

7 

0 

6 

1-0078 

0 

1 

9-75C 

2 

6 

0 

5 

11-6803 

0 

1 

9-125 

2 

5 

0 

5 

10-3529 

0 

1 

8-500 

2 

4 

0 

5 

9-0255 

0 

1 

7-875 

1 

2 

3 

0 

5 

7-6981 

0 

1 

7-250 

1 

2 

2 

0 

5 

6-3707 

0 

1 

6-625 

1 

2 

1 

0 

5 

5-0433 

0 

1 

6-000 

1 

2 

0 

0 

5 

3-7159 

0 

] 

5-375 

1 

1 

7 

0 

5 

2-3884 

0 

1 

4-750 

1 

1 

6 

0 

5 

1-0610 

0 

1 

4-125 

1 

1 

5 

0 

4 

11-7336 

0 

1 

3-500 

1 

1 

4 

0 

4 

10-4062 

0 

1 

2-875 

1 

1 

3 

0 

4 

9-0788 

0 

1 

2-250 

1 

1 

2 

0 

4 

7-7514 

0 

1 

1-625 

1 

1 

1 

0 

4 

6-4240 

0 

1 

1-000 

1 

1 

0 

0 

4 

5-0965 

0 

1 

0-375 

1 

0 

7 

0 

4 

3-7691 

0 

0 

23-750 

1 

0 

6 

0 

4 

2-4417 

0 

0 

23-125 

1 

0 

5 

0 

4 

1-1143 

0 

0 

22-500 

1 

0 

4 

0 

3 

11-7869 

0 

0 

21-875 

1 

0 

3 

0 

3 

10-4595 

0 

0 

21-250 

1 

0 

2 

0 

3 

9-1321 

0 

0 

20-625 

1 

0 

1 

0 

3 

78046 

0 

0 

20-000 

1 

0 

0 

0 

3 

6-4772 

0 

0 

19-375 

0 

3 

7 

0 

3 

5-1498 

0 

0 

18-750 

0 

3 

6 

0 

3 

3-8224 

GOLD-VALUING   TABLE. 


XIX 


FINE  .GOLD, 

Per  Ounce 

CARAT  GOLD, 

Per  Ounce 

STEELING  VALUE 

Per  Ounce 

Oz. 

Dwts. 

Grs. 

Carats 

Grs. 

Eighths 

£ 

s. 

,* 

0 

0 

18-125 

0 

3 

5 

0 

3 

2-4950 

0 

0 

17-500 

0 

3 

4 

0 

3 

1-1676 

0 

0 

16-875 

0 

3 

3 

0 

2 

11-8401 

0 

0 

16-250 

0 

3 

2 

0 

2 

10-5127 

0 

0 

15-625 

0 

3 

1 

0 

2 

9-1853 

0 

0 

15-000 

0 

3 

0 

0 

2 

7-8579 

0 

0 

1  4-375 

0 

2 

7 

0 

2 

6-5305 

0 

0 

13-750 

0 

2 

6 

0 

2 

5-2031 

0 

0 

13-125 

0 

2 

5 

0 

2 

3-8757 

0 

0 

12-500 

0 

2 

4 

0 

2 

2-5482 

0 

0 

11-875 

0 

2 

3 

0 

2 

1-2208 

0 

0 

11-250 

0 

2 

2 

0 

1 

11-8934 

0 

0 

10-625 

0 

2 

1 

0 

1 

10-5660 

0 

0 

10-000 

0 

2 

0 

0 

1 

9-2386 

0 

0 

9-375 

0 

1 

7 

0 

1 

7-9112 

0 

0 

8-750 

0 

1 

6 

0 

1 

6-5838 

0 

0 

8-125 

o 

1 

5 

0 

1 

5-2563 

0 

0 

7-500 

0 

1 

4 

0 

1 

3-9289 

0 

0 

6-875 

0 

1 

3 

0 

1 

2-6015 

0 

0 

6-250 

0 

1 

2 

0 

1 

1-2741 

0 

0 

5-625 

0 

1 

L 

0 

0 

11-9467 

0 

0 

5-000 

0 

1 

0 

0 

0 

10-6193 

0 

0 

4-375 

0 

0 

7 

0 

0 

9-2919 

0 

0 

3-750 

0 

0 

6 

0 

0 

7-9644 

0 

0 

3-125 

0 

0 

5 

0 

0 

6-6370 

0 

0 

2-500 

0 

0 

4 

0 

0 

5-3096 

0 

0 

1-875 

0 

0 

3 

0 

0 

3-9822 

0 

0 

1-250 

0 

0 

2 

0 

0 

2-6548 

0 

0 

0-625 

0 

0 

1 

0 

0 

1-3274 

GOLD-VALUING   TABLE. 


To  convert  MINT  VALUE  into  BANK  VALUE  when  the  Standard 
is  expressed  in  Carats,  Grains,  and  Eighths.  This  can  be 
readily  accomplished  for  every  report  by  the  following 
Tables*:— 

TABLE  A. 


CARATS 

VALUE  IN  PENCE 

CARATS 

VALUE  IN  PENCE 

1 

•0681 

13 

•8863 

2 

•1363 

14 

•9545 

3 

•2045 

15 

1-0227 

4 

•2727 

16 

1-0909 

5 

•3409 

17 

1-1590 

6 

•4090 

18 

•2272 

7 

•4772 

19 

•2954 

8 

•5454 

20 

•3636 

9 

•6136 

21 

•4318 

10 

•6818 

22 

•5000 

11 

•7500 

23 

•5681 

12 

•8181 

24 

1-6363 

TABLE  B. 


CARAT  GRAINS 

VALUE  IN  PENCE 

CARAT  GRAINS 

VALUE  IN  PENCE 

1 

2 

•0170 
•0340 

3 

4 

•0511 
•0681 

TABLE  C. 


EIGHTH  CARAT 
GRAINS 

VALUE  IN  PENCE 

EIGHTH  CARAT 
GRAINS 

VALUE  IN  PENCE 

1 

•0021 

5 

•0106 

2 

•0042 

6 

•0127 

3 

•0063 

7 

•0149 

4 

•0085 

8 

•0170 

GOLD-VALUING   TABLE. 


XXI 


Table  A  gives  the  difference  in  price  between  Mint  and  Bank 
value  for  each  carat  up  to  fine  gold  ;  Table  B  the  same  for  carat 
grains  ;  and  Table  C  the  same  for  eighths  of  carat  grains. 

Now  as  the  Bank  value  of  gold  is  £3  17 s.  9d.  per  oz.  standard 
against  Mint  value  of  £3  17s.  10^<i.,  it  follows  by  calculation 
that  fine  gold  would  fetch,  Bank  price,  only  £4  4s.  9*8182(2., 
instead  of  £4  4s.  ll*4545<i.,  as  shown  by  Table  I.  of  Mint 
Values  ;  and  the  Bank  value  of  1  oz.  of  gold,  of  any  standard 
whatever,  may  be  readily  ascertained  by  the  above  Tables  A, 
B,  and  C,  and  Table  I.— the  Tables  A,  B,  and  C,  giving  the 
quantities  in  pence  to  be  deducted  from  the  corresponding  stan- 
dard in  Table  I.  Thus,  suppose  it  is  necessary  to  ascertain  the 
Bank  value  of  1  oz.  of  gold  of  14  carats  2  grains  5  eighths  fine : 
refer  to  Table  A,  at  14  carats  is  found  -9545<i. ;  at  2  grains  in 
Table  B  is  found  -0340d. ;  and  at  5  eighths  in  Table  C  -0106cZ. 
Xow  -9545  + -0340-^0106  =  -9991,  which  has  to  be  deducted 
from  £2  Us.  10'5575d.  (see  Table  I.),  leaving  £2  Us.  9-5564d.as 
the  Bank  value  of  1  oz.  of  gold  of  the  above  fineness. 


TABLE  II. 

TABLE  of  relative  proportions  of  FINE  GOLD  and  ALLOY,  with 
the  respective  Mint  Values  of  1  oz.  of  each  Alloy  when  the 
Standard  is  expressed  in  Thousandths. 


FIXE 
GOLD 

ALLOY 

VALUE 

FINK 
GOLD 

ALLOY 

VALUE 

£      s.      d. 

£      s.      d. 

1000 

•000 

4     4  11-4545 

986 

•014 

4     3     9-1821 

999 

•001 

4     4   10-4350 

985 

•015 

4     3     8-1627 

998 

•002 

4     4     9-4156 

984 

•016 

4     3     7-1432 

997 

•003 

4     4     8-3961 

983 

•017 

4     3     6-1238 

996 

•004 

4     4     7-3767 

982 

•018 

4     3     5-1043 

995 

•005 

4     4     6-3572 

981 

•019 

4     3     4-0849 

994 

•006 

4     4     5-3378 

980 

•020 

4     3     3-0654 

993 

•007 

4     4     4-3183 

979 

•021 

4     3     2-0459 

992 

•008 

4     4     3-2989 

978 

•022 

4     3     1-0265 

991 

•009 

4     4     2-2793 

977 

•023 

4     3     0-0070 

990 

•010 

4     4     1-2600 

976 

•024 

4     2  10-9876 

989 

•Oil 

4     4     0*2405 

975 

•025 

4     2     9-9681 

988 

•012 

4     3  11-2210 

974 

•026 

4     2     8-9487 

987 

•013 

4     3  10-2016 

973 

•027 

4     2     7-9292 

XX11 


GOLD-VALUING   TABLE. 


FINE 
GOLD 

ALLOY 

VALUE 

GOLD 

ALLOY 

VALUE 

£  s.  d. 

£   a.  d. 

972 

•028 

4  2  6-9098 

929 

•071 

3  18  11-0732 

971 

•029 

4  2  5-8903 

928 

•072 

3  18  10-0538 

970 

•030 

4  2  4-8709 

927 

•073 

3  18  9-0343 

969 

•031 

4  2  3-8504 

9-^6 

•074 

3  18  8-0149 

968 

•032 

4  2  2-8319 

925 

•075 

3  18  6-9954 

967 

•033 

4  2  1-8125 

924 

•076 

3  18  5-9759 

966 

•034 

4  2  0-7930 

923 

•077 

3  18  4-9565 

965 

•035 

4    11-7736 

922 

•078 

3  18  3-9370 

964 

•036 

4    10-7541 

921 

•079 

3  18  2-9176 

963 

•037 

4     9-7347 

920 

•080 

3  18  1-8981 

962 

•038 

4     8-7152 

919 

•081 

3  18  0-8787 

961 

•039 

4     7-6958 

918 

•082 

3  17  11-8592 

960 

•040 

4     6-6763 

917 

•083 

3  17  10-8398 

959 

•041 

4  1  5-6569 

916* 

•084 

3  17  9-8203 

958 

•042 

4  1  4-6374 

915 

•085 

3  17  8-8009 

957 

•043 

4  1  3-6179 

914 

•086 

3  17  7-7814 

956 

•044 

4  1  2-5985 

913 

•087 

3  17  6-7619 

955 

•045 

4  1  1-5790 

912 

•088 

3  17  5-7425 

954 

•046 

4  1  0-5596 

911 

•089 

3  17  4-7230 

953 

•047 

4  0  11-5401 

910 

•090 

3  17  3-7036 

952 

•048 

4  0  10-5207 

909 

•091 

3  17  2-6841 

951 

•049 

4  0  9-5012 

908 

•092 

3  17  1-6647 

950 

•050 

4  0  8-4818 

907 

•093 

3  17  0-6452 

949 

•051 

4  0  7-4623 

906 

•094 

3  16  11-6258 

948 

•052 

4  0  6-4429 

905 

•095 

3  16  10-6063 

947 

•053 

4  0  5-4234 

904 

•096 

3  16  9-5869 

946 

•054 

4  0  4-4039 

903 

•097 

3  16  8-5674 

945 

•055 

4  0  3-3835 

902 

•098 

3  16  7-5479 

944 

•056 

4  0  2-3650 

901 

•099 

3  16  6-5285 

943 

•057 

4  0  1-3456 

900 

•100 

3  16  5-5090 

942 

•058 

4  0  0-3261 

899 

•101 

3  16  4-4896 

941 

•059 

3  19  11-3067 

898 

•102 

3  16  3-4701 

940 

•060 

3  19  10-2872 

897 

•103 

3  16  2-4507 

939 

•061 

3  19  9-2678 

896 

•104 

3  16  1-4312 

938 

•062 

3  19  8-2483 

895 

•105 

3  16  0-4118 

937 

•063 

3  19  7-2289 

894 

•106 

3  15  11-3923 

936 

•064 

3  19  6-2094 

893 

•107 

3  15  10-3729 

935 

•065 

3  19  5-1899 

892 

•108 

3  15  9-3534 

934 

•066 

3  19  4-1705 

891 

•109 

3  15  8-3339 

933 

•067 

3  19  3-1510 

890 

•110 

3  15  7-3145 

932 

•068 

3  19  2-1316 

889 

•111 

3  15  6-2950 

931 

•069 

3  19  1-1121 

888 

•112 

3  15  5-2756 

930 

•070 

3  19  0-0927 

887 

•113 

3  15  4-2561 

*  916-666  Standard  -083-333  £B  17s.  10"5000<2. 


GOLD-VALUING   TABLE. 


XXlll 


FINE 
GOLD 

ALLOY 

VALTJB 

FINE 
GOLD 

ALLOT 

VALUE 

£  s.  d. 

£  «.  d. 

886 

•114 

3  15  3-2367 

841 

•159 

3  11  5-3612 

885 

•115 

3  15  2-2172 

840 

•160 

3  11  4-3418 

884 

•116 

3  15  1-1978 

839 

•161 

3  11  3-3223 

883 

•117 

3  15  0-1783 

838 

•162 

3  11  2-3029 

882 

•118 

3  14  11-1589 

837 

•163 

3  11  1-3834 

881 

•119 

3  14  10-1394 

836 

•164 

3  11  0-2639 

880 

•120 

3  14  9-1199 

835 

•165 

3  10  11-2445 

879 

•121 

3  14  8-1005 

834 

•166 

3  10  10-2250 

878 

•122 

3  14  7-0810 

833 

•167 

3  10  9-2056 

877 

•123 

3  14  6-0616 

832 

•168 

3  10  8-1861 

876 

•124 

3  14  5-0421 

831 

•169 

3  10  7-1667 

875 

•125 

3  14  4-0227 

830 

•170 

3  10  6-1472 

874 

•126 

3  14  3-0032 

829 

•171 

3  10  5-1278 

873 

•127 

3  14  1-9838 

828 

•172 

3  10  4-1083 

872 

•128 

3  14  0-9643 

827 

•173 

3  10  3-0889 

871 

•129 

3  13  11-9449 

826 

•174 

3  10  2-0694 

870 

•130 

3  13  10-9254 

825 

•175 

3  10  1-0499 

869 

•131 

3  13  9-9059 

824 

•176 

3  10  0-0305 

868 

•132 

3  13  8-8865 

823 

•177 

3  9  11-0110 

867 

•133 

3  13  7-8670 

822 

•178 

3  9  9-9916 

866 

•134 

3  13  6-8476 

821 

•179 

3  9  8-9721 

865 

•135 

3  13  5-8281 

820 

•180 

3  9  7-9527 

864 

•136 

3  13  4-8087 

819 

•181 

3  9  6-9332 

863 

•137 

3  13  3-7892 

818 

•182 

3  9  5-9138 

862 

•138 

3  13  2-7698 

817 

•183 

3  9  4-8943 

861 

•139 

3  13  1-7503 

816 

•184 

3  9  3-8749 

860 

•140 

3  13  0-7309 

815 

•185 

3  9  2-8554 

859 

•141 

3  12  11-7114 

814 

•186 

3  9  1-8359 

858 

•142 

3  12  10-6919 

813 

•187 

3  9  0-8165 

857 

•143 

3  12  9-6725 

812 

•188 

3  8  11-7970 

856 

•144 

3  12  8-6530 

811 

•189 

3  8  10-7776 

855 

•145 

3  12  7-6336 

810 

•190 

3  8  9-7581 

854 

•146 

3  12  6-6141 

809 

•191 

3  8  8-7387 

853 

•147 

3  12  5-5947 

808 

•192 

3  8  7-7192 

852 

•148 

3  12  4-5752 

807 

•193 

3  8  6-6998 

851 

•149 

3  12  3-5558 

806 

•194 

3  8  5-6803 

850 

•150 

3  12  2-5363 

805 

•195 

3  8  4-6609 

849 

•151 

3  12  1-5169 

804 

•196 

3  8  3-6414 

848 

•152 

3  12  0-4974 

803 

•197 

3  8  2-6219 

847 

•153 

3  11  11-4779 

802 

•198 

3  8  1-6025 

846 

•154 

3  11  10-4585 

801 

•199 

3  8  0-5830 

845 

•155 

3  11  9-4390 

800 

•200 

3  7  11-5636 

844 

•156 

3  11  8-4196 

799 

•201 

3  7  10-5441 

843 

•157 

3  11  7-4001 

798 

•202 

3  7  9-5247 

842 

•158 

3  11  6-3807 

797 

•203 

3  7  8-5052 

XXIV 


-GOLD-VALUING   TABLE. 


FINE 
GOLD 

ALLOY 

VALUE 

FINE 
GOLD 

ALLOY 

VALTJE 

£     s.     d. 

'  £     s.    d. 

796 

•204 

3     7     7-4858 

751 

•249 

3     3     9-6103 

795 

•205 

3     7     6-4663 

750 

•250 

3     3     8-5909 

794 

•206 

3     7     5-4469 

749 

•251 

3     3     7-5714 

793 

•207 

3     7     4-4274 

748 

•252 

3     3     6-5519 

792 

•208 

3     7     3-4979 

747 

•253 

3     3     5-5325 

791 

•209 

3     7     2-3885 

746 

•254 

3     3     4-5130 

790 

•210 

3     7     1-3690 

745 

•255 

3     3     3-4936 

789 

•211 

3     7     0-3496 

744 

•256 

3     3     2-4741 

788 

•212 

3     6  11-3301 

743 

•257 

3     3     1-4547 

787 

•213 

3     6  10-3107 

742 

•258 

3     3     0-4352 

786 

•214 

3     6     9-2912 

741 

•259 

3     2  11-4158 

785 

•215 

3     6     8-2718 

740 

•260 

3     2  10-3963 

784 

•216 

3     6     7-2523 

739 

•261 

3     2     9-3769 

783 

•217 

3     6     6-2329 

738 

•262 

3     2     8-3574 

782 

•218 

3     6     5-2134 

737 

•263 

3     2     7-3379 

781 

•219 

3     6     4-1939 

736 

•264 

3     2     6-3185 

780 

•220 

3     6     3-1745 

735 

•265 

3     2     5-2990 

779 

•221 

3     6     2-1550 

734 

•266 

3     2     4-2796 

778 

•222 

3     6     1-1356 

733 

•267 

3     2     3-2601 

777 

•223 

3     6     0-1161 

732 

•268 

3     2     2-2407 

776 

•224 

3     5  11-0967 

731 

•269 

3     2     1-2212 

775 

•225 

3     5  10-0772 

730 

•270 

3     2     0-2018 

774 

•226 

3     5     9-0578 

729 

•271 

3     1   11-1823 

773 

•227 

3     5     8-0383 

728 

•272 

3     1   10-1629 

772 

•228 

3     5     7-0189 

727 

•273 

3     1     9-1434 

771 

•229 

3     5     5-9994 

726 

•274 

3     1     8-1239 

770 

•230 

3     5     4-9799 

725 

•275 

3     1     7-1045 

769 

•231 

3     5     3-9605 

724 

•276 

3     1     6-0850 

768 

•232 

3     5     2-9410 

723 

•277 

3     1     5-0656 

767 

•233 

3     5     1-9216 

722 

•278 

3     1     4-0461 

766 

•234 

3     5     0-9021 

721 

•279 

3     1     3-0267 

765 

•235 

3     4  11-8827 

720 

•280 

3     1     2-0072 

764 

•236 

3     4  10-8632 

719 

•281 

3     1     0-9878 

763 

•237 

3     4     9-8438 

718 

•282 

3     0  11-9683 

762 

•238 

3     4     8-8243 

717 

•283 

3     0  10-9489 

761 

•239 

3     4     7-8049 

716 

•284 

3     0     9-9294 

760 

•240 

3     4     6-7854 

715 

•285 

3     0     8-9099 

759 

•241 

3     4     5-7659 

714 

•286 

3     0     7-8905 

758 

•242 

3     4     4-7465 

713 

•287 

3     0     6-8710 

757 

•243 

3     4     3-7270 

712 

•288 

3     0     5-8516 

756 

•244 

3     4     2-7076 

711 

•289 

3     0     4-8321 

755 

•245 

3     4     1-6881 

710 

•290 

3     0     3-8127 

754 

•246 

3     4     0-6687 

709 

•291 

3     0     2-7932 

753 

•247 

3     3  11-6492 

708 

•292 

3     0     1-7738 

752 

•248 

3     3  10-6298 

707 

•293 

3     0     0-7543 

GOLD-VALUING   TABLE. 


XXV 


FIXE 
GOLD 

ALLOY 

VALUE 

FIXE 
GOLD 

ALLOY 

VALUE 

£  *.   d. 

£  s.   d. 

706 

•294 

2  19  11-7349 

661 

•339 

2  16  1-8594 

705 

•295 

2  19  10-7154 

660 

•340 

2  16  0-8399 

704 

•296 

2  19  9-6959 

659 

•341 

2  15  11-8205 

703 

•297 

2  19  8-6765 

658 

•342 

2  15  10-8010 

702 

•298 

2  19  7-6570 

657 

•343 

2  15  9-7816 

701 

•299 

2  19  6-6376 

656 

•344 

2  15  8-7621 

700 

•300 

2  19  5-6181 

655 

-345' 

2  15  7-7427 

699 

•301 

2  19  4-5987 

654 

•346 

2  15  6-7232 

698 

•302 

2  19  3-5732 

653 

-347 

2  15  5-7038 

697 

•303 

2  19  2-5598 

652 

•348 

2  15  4-6843 

696 

•304 

2  19  1-5403 

651 

-349' 

2  15  3-6649 

695 

•305 

2  19  0-5209 

650 

•350 

2  15  2-6454 

694 

•306 

2  18  11-5014 

649 

•351 

2  15  1-6259 

693 

•307 

2  18  10-4820 

648 

•352 

2  15  0-6065 

692 

•308 

2  18  9-4625 

647 

•353. 

2  14  11-5870 

691 

•309 

2  18  8-4430 

646 

•354 

2  14  10-5676 

690 

•310 

2  18  7-4236 

645 

•355 

2  14  9-5481 

689 

•311 

2  18  6-4041 

644 

•356 

2  14  8-5287 

688 

•312 

2  18  5-3847 

643 

•357 

2  14  7-5092 

687 

•313 

2  18  4-3652 

642 

•358 

i  2  14  6-4898 

686 

•314 

2  18  3-3458 

641 

•359 

2  14  5-4703 

685 

•315 

2  18  2-3263 

640 

•360* 

'  2  14  4-4509 

684 

•316 

2  18  1-3069 

639 

•361 

;  2  14  3-4314 

683 

•317 

2  18  0-2874 

638 

•362 

2  14  2-4120 

682 

•318 

2  17  11-2680 

637 

•363 

i  2  14  1-3925 

681 

•319 

2  17  10-2485 

636 

•364 

2  14  0-3730 

680 

•320 

2  17  9-2290 

635 

•365 

,  2  13  11-3536 

679 

•321 

2  17  8-2096 

634 

•366 

2  13  10-3341 

678 

•322 

2  17  7-1901 

633 

•367 

2  13  9-3147 

677 

•323 

2  17  6-1707 

632 

•368 

2  13  8-2952 

676 

•324 

2  17  5-1512 

631 

•369 

2  13  7-2758 

675 

•325 

2  17  4-1318 

630 

•370 

2  13  6-2563 

674 

•326 

2  17  3-1123 

629 

•371 

2  13  5-2369 

673 

•327 

2  17  2-0929 

628 

•372 

2  13  4-2174 

672 

•328 

2  17  1-0734 

627 

•37  a 

2  13  3-1979 

671 

•329 

2  17  0-0540 

626 

•374 

2  13  2-1785 

670 

•330 

2  16  11-0345 

625 

-375 

2  13  1-1590 

669 

•331 

2  16  10-0151 

624 

•376. 

2  13  0-1396 

668 

•332 

2  16  8-9956 

623 

•377 

2  12  11-1201 

667 

•333 

2  16  7-9761 

622 

•378 

2  12  10-1007 

666 

•334 

2  16  6-9567 

621 

•379 

2  12  9-0812 

665 

•335 

2  16  5-9372 

620 

•380 

.2  12  8-0618 

664 

•336 

2  16  4-9178 

619 

•381 

2  12  7-0423 

663 

•337 

.2  16  3-8983 

618 

•382 

2  12  6-0229 

662 

•338 

i  2  16  2-8789. 

6J7 

;383  i  2  12  5-0034 

XXVI 


GOLD-VALUING   TABLE. 


FINE 
GOLD 

ALLOY 

VALUE 

FINE 
GOLD 

ALLOY 

VALUE 

£   s.  d. 

£   s.  d. 

616 

•384 

2  12  3-9839 

571 

•429 

2  8  6-1085 

615 

•385 

2  12  2-9645 

570 

•430 

2  8  5-0890 

614 

•386 

2  12  1-9451 

569 

•431  • 

2  8  4-0696 

613 

•387 

2  12  0-9256 

568 

•432 

2  8  3-0501 

612 

•388 

2  11  11-9061 

567 

•433 

2  8  2-0307 

611 

•389 

2  11  10-8867 

566 

•434 

2  8  1-0112 

610 

•390 

2  11  9-8672 

565 

•435 

2  7  11-9918 

609 

•391 

2  11  8-8478 

564 

•436 

2  7  10-9723 

608 

•392 

2  11  7-8283 

563 

•437 

2  7  9-9529 

607 

•393 

2  11  6-8089 

562 

•438 

2  7  8-9334 

606 

•394 

2  11  5-7894 

561 

•439 

2  7  7-9140 

605 

•395 

2  11  4-7699 

560 

•440 

2  7  6-8945 

604 

•396 

2  11  3-7505 

559 

•441 

2  7  5-8751 

603 

•397 

2  11  2-7311 

558 

•442 

2  7  4-8556 

602 

•398 

2  11  1-7116 

557 

•443 

2  7  3-8361 

601 

•399 

2  11  0-6921 

556 

•444 

2  7  2-8167 

600 

•400 

2  10  11-6727 

555 

•445 

2  7  1-7972 

599 

•401  i 

2  10  10-6532 

554 

•446 

2  7  0-7778 

598 

•402 

2  10  9-6338 

553 

•447 

2  6  11-7583 

597 

-403 

2  10  8-6143 

552 

•448 

2  6  10-7389 

596 

•404 

2  10  7-5949 

551 

•449 

2  6  9-7194 

595 

•405 

2  10  6-5754 

550 

•450 

2  6  8-6999 

594 

•406 

2  10  5-5559 

549 

•451 

2  6  7-6805 

593 

•407 

2  10  4-5365 

548 

•452 

2  6  6-6611 

592 

•408 

2  10  3-5170 

547 

•453 

2  6  5-6416 

591 

-409 

2  10  2-4976 

546 

•454 

2  6  4-6221 

590 

•410 

2  10  1-4781 

545 

•455 

2  6  3-6027 

589 

-411 

2  10  0-4587 

544 

•456 

2  6  2-5832 

588 

-412 

2  9  11-4392 

543 

•457 

2  6  1-5638 

587 

•413 

2  9  10-4198 

542 

•458 

2  6  0-5443 

586 

•414 

2  9  9-4003 

541 

•459 

2  5  11-5249 

585 

•415 

2  9  8-3809 

540 

•460 

2  5  10-5054 

584 

•416  • 

2  9  7-3614 

539 

•461 

2  5  9-4859 

583 

•417 

2  9  6-3419 

538 

•462 

2  5  8-4665 

582 

•418 

2  9  5-3225 

537 

•463 

2  5  7-4470 

581 

•419 

2  9  4-3030 

536 

•464 

2  5  6-4276 

580 

•420 

2  9  3-2836 

535 

•465 

2  5  5-4081 

579 

•421 

2  9  2-2641 

534 

•466 

2  5  4-3887 

578 

•422 

2  9  1-2447 

533 

•467 

2  5  3-3692 

577 

•423 

2  9  0-2252 

532 

•468 

2  5  2-3498 

576 

•424 

2  8  11-2058 

531 

•469 

2  5  1-3303 

575 

•425 

2  8  10-1863 

530 

•470 

2  5  0-3109 

574 

•426 

2  8  9-1669 

529 

•471 

2  4  11-2914 

573 

•427 

2  8  8-1474 

528 

•472 

2  4  10-2719 

572 

•428 

2  8  7-1279 

527 

•473 

2  4  9-2525 

GOLD-VALUING   TABLE. 


XXV11 


FINE 
GOLD 

ALLOY 

VALUB 

FINE 
GOLD 

ALLOY 

VALUE 

£   s.  d. 

£   *.  d. 

526 

•474 

2  4  8-2330 

481 

•519 

2  0  10-3576 

525 

•475 

2  4  7-2136 

480 

•520 

2  0  9-3381 

524 

•476 

2  4  6-1941 

479 

•521 

2  0  8-3187 

523 

•477 

2  4  5-1747 

478 

•522 

2  0  7-2992 

522 

•478 

2  4  4-1552 

477 

•523 

2  0  6-2798 

521 

•479 

2  4  3-1358 

476 

•524 

2  0  5-2603 

520 

•480 

2  4  2-1163 

475 

•525 

2  0  4-2409 

519 

•481 

2  4  1-0969 

474 

•526 

2  0  3-2214 

518 

•482 

2  4  0-0774 

473 

•527 

2  0  2-2020 

517 

•483 

2  3  11-0579 

472 

•528 

2  0  1-1825 

516 

•484 

2  3  10-0385 

471 

•52£ 

2  0  0-1630 

515 

•485 

2  3  9-0190 

470 

•530 

1  19  11-1436 

514 

•486 

2  3  7-9996 

469 

•531 

1  19  10-1241 

513 

•487 

2  3  6-9801 

468 

•532 

1  19  9-1047 

512 

•488 

2  3  5-9607 

467 

•533 

1  19  8-0852 

511 

•489 

2  3  4-9412 

466 

•534 

1  19  7-0658 

510 

•490 

2  3  3-9218 

465. 

i  -535 

1  19  6-0463 

509 

•491 

2  3  2-9023 

464 

•536 

1  19  5K)269 

508 

•492 

2  3  1-8829 

463> 

•537 

1  19  4-0074 

507 

•493 

2  3  0-8634 

462 

,  -538 

1  19  2-9879 

506 

•494 

2  2  11-8439 

461 

•539 

1  19  1-9685 

505 

•495 

2  2  10-8245 

460; 

•540, 

1  19  0-9490 

504 

•496 

2  2  9-8051 

45-9. 

•541 

1  18  11-9296 

503 

•497 

2  2  8-7856 

458 

•542 

1  18  10-9101 

502 

•498 

2  2  7-7661 

457 

•543. 

1  18  9-8907 

501 

•499 

2  2  6-7467 

456 

-544 

1  18  8-8712 

500 

•500 

2  2  5-7272 

455 

•545 

1  18  7-8518 

499 

•501 

2  2  4-7078 

454 

•546 

1  18  6-8323 

498 

•502 

2  2  3-6883 

453 

•547 

1  18  5-8129 

497 

•503 

2  2  2-6689 

452 

•548 

li  18  4-7934 

496 

•504 

2  2  1-6494 

451 

•549 

1  18  3-7739 

495 

•505 

2  2  0-6300 

450 

•550 

1  18  2-7545- 

494 

•506 

2  1  11-6105 

449 

•551 

1  18  1-7351 

493 

•507 

2  1  10-5911 

448 

•552. 

1  18  0-7156' 

492 

•508 

2  1  9-5716 

447 

•553 

1  17  11-696L 

491 

•509 

2  1  8-5521 

446 

•554 

1  17  10-67677 

490 

•510 

2  1  7-5327 

445 

•555 

1  17  9-6572 

489 

•511 

2  1  1-5132 

444 

•556 

1  17  8-6378 

488 

•512 

2  1  5-4938 

443 

•557 

1  17  7-6183- 

487 

•513 

2  1  4-4743 

442 

•558 

1  17  6-5989 

486 

•514 

2  1  3-4549 

441 

•559 

1  17  5-5794 

485 

•515 

2  1  2-4354 

440 

•560 

1  17  4-5599 

484 

•516 

2  1  1-4159 

439 

•561 

1  17  3-5405 

483 

•517 

2  1  0-3965 

438 

•562 

1  17  2-5211 

482 

•518 

2  0  11-3770 

437 

•563 

1  17  1-5016 

XXV11I 


GOLD-VALUING   TABL  E.  } 


FINE 

'GOLD 

ALLOY 

VALUE 

FINE 
GOLD 

ALLOY 

VALUE 

£   s.  d. 

£  *.  d.  \ 

436 

•564 

I  17  0-4821 

391 

•609 

l:  13  2-6067 

435 

•565 

1  16  11-4627 

390 

•610 

I-  13  1-5872 

434 

-566 

1  16  10*4432 

389 

•611 

1  13  0-5678 

433 

*567 

1  16  9-4238 

388 

•612 

1  12  11-5483 

432 

-568 

1  16  8-4043 

387 

•613 

1  12  10-5289 

431 

-569 

1  16  7-3849 

386 

•614 

1  12  9-5094 

430 

-570 

1  16  6-3654 

385 

•615 

1  12  8-4899 

429 

•571 

1  16  5-3459 

384 

•616 

1  12  7-4705 

428 

-572 

1  16  4-3265 

383 

•617 

1  12  6-4511 

427 

-573 

1  16  3-3070 

382 

•618 

1  12  5-4316 

426 

•574 

1  16  2-2876 

381 

•619 

1  12  4-4121 

425 

•575 

1  16  1-2681 

380 

•620 

1  12  3-3927 

424 

•576 

1  16  0-2487 

379 

•621 

1  12  2-3732 

423 

•577 

1  15  11-2292 

378 

•622 

1  12  1-3538 

422 

•578 

1  15  10-2098 

377 

•623 

1  12  0-3343 

421 

•579 

1  15  9-1903 

376 

•624 

1  11  11-3142 

420 

•580 

1  15  8-1709 

375 

•625 

1  11  10-2954 

419 

•581 

1  15  7-1514 

374 

•626 

1  11  9-2759 

418 

•582 

1  15  6-1319 

373 

•627 

1  11  8-2565 

417 

•583 

1  15  5-1125 

372 

•628 

1  11  7-2370 

41*6 

•584 

1  15  4-0930 

371 

•629 

1  11  6-2176 

415 

•585 

1  15  3-0736 

370 

•630 

1  11  5-1981 

414 

•586 

1  15  2-0541 

369 

•631 

1  11  4-1787 

413 

•587 

1  15  1-0347 

368 

•632 

1  11  3-1592 

412 

•588 

1  15  0-0152 

367 

•C33 

1  11  2-1398 

411 

•589 

1  14  10-9958 

366 

•634 

1  11  1-1203 

410 

•590 

1  14  9-9763 

365 

•635 

1  11  0-1009 

409 

•591 

1  14  8-9569 

364 

•636 

1  10  11-0814 

408 

•592 

1  14  7-9374 

363 

•637 

1  10  10-0620 

407 

•593 

1  14  6-9179 

362 

•638 

1  10  9-0425 

406 

•594 

1  14  5-8985 

361 

•639 

1  10  8-0230 

405 

•595 

1  14  4-8790 

360 

•640 

1  10  7-0036 

404 

•596 

1  14  3-8596 

359 

•641 

1  10  5-9841 

403 

•597 

1  14  2-8401 

358 

•642 

1  10  4-9647 

402 

•598 

1  14  1-8207 

357 

•643 

1  10  3-9452 

401 

•599 

1  14  0-8012 

356 

•644 

1  10  2-9258 

400 

.600 

1  13  11-7818 

355 

•645 

1  10  1-9063 

399 

•601 

1  13  10-7623 

354 

•646 

1  10  0-8869 

398 

•602 

1  13  9-7429 

353 

•647 

1  9  11-8674 

397 

•603 

1  13  8-7234 

352 

•648 

1  9  10-8479 

396 

•604 

1  13  7-7039 

351 

•649 

1  9  9-8285 

395 

•605 

1  13  6-6845 

350 

•650 

1  9  8-8090 

394 

•606 

1  13  5-6651 

349 

•651 

1  9  7-7896 

393 

•607 

1  13  4-6456 

348 

•652 

1  9  6-7701 

392 

•608 

1  13  3-6261 

347 

•653 

1  9  5-7507 

GOLD- VALUING   TABLE. 


xxix 


FlNB 

GOLD 

AlXOT 

- 
VALUB 

FINK 
GOJJ> 

AlXOT 

VALTJB 

£      s.      d. 

£      9.      d. 

346 

•654 

I     9     4-7312 

301 

•699 

1     5     6-8558 

345 

•655 

1     9     3-7118 

300 

•700 

1     5     5-8363 

344 

•656 

1     9     2-6923 

299 

•701 

1     5     4-8169 

343 

•657 

1     9     1-6729 

298 

•702 

1     5     3-7974 

342 

•658 

1     9     0-6534 

297 

•703 

I     5     2-7779 

341 

•659 

1     8  11-6339 

296 

•704 

1     5     1-7585 

340 

•660 

1     8  10-6145 

295 

•705 

1     5     0-7390 

339 

•661 

1     8     9-5951 

294 

•706 

1     4  11-7196 

338 

•662 

1     8     8-5756 

293 

•707 

1     4  10-7011 

337 

•663 

1     8     7-5561 

292 

•708 

1     4     9-6807 

336 

•664 

1     8     6-5367 

291 

•709 

1     4     8-6612 

335 

•665 

1     8     5-5172 

290 

•710 

1     4     7-6418 

334 

•666 

1     8     4-4978 

289 

•711 

1     4     6-6223 

333 

•667 

1     8     3-4783 

288 

•712 

1     4     5-6029 

332 

•668 

1     8     2-4589 

287 

•713 

1     4     4-5834 

331 

•669 

1     8     1-4394 

286 

•714 

1     4     3-5639 

330 

•670 

1     8     0-4199 

285 

•715 

1     4     2-5445 

329 

•671 

1     7  11-4005 

284 

•716 

1     4     1-5251 

328 

•672 

1     7  10-3811 

283 

•717 

1     4     0-5056 

327 

•673 

1     7     9-3616 

282 

•718 

1     3  11-4861 

326 

•674 

1     7     8-3421 

281 

•719 

1     3  10-4667 

325 

•675 

1     7     7-3227 

280 

•720 

1     3     9-4472 

324 

•676 

1     7     6-3032 

279 

•721 

1     3     8-4278 

323 

•677 

1     7     5-2838 

278 

•722 

1     3     7-4083 

322 

•678 

1     7     4-2643 

277 

•723 

1     3     6-3889 

321 

•679 

1     7     3-2449 

276 

•724 

1     3     5-3694 

320 

•680 

1     7     2-2254 

275 

•725 

1     3     4-3499 

319 

•681 

1     7     1-2059 

274 

•726 

1     3     3-3305 

318 

•682 

1     7     0-1865 

273 

•727 

1     3     2-3110 

317 

•683 

1     6  11-1670 

272 

•728 

1     3     1-2916 

316 

•684 

1     6  10-1476 

271 

•729 

1     3     0-2721 

315 

•685 

1     6     9-1281 

270 

•730 

1     2  11-2527 

314 

•686 

1     6     8-1087 

269 

•731 

1     2  10-2332 

313 

•687 

1     6     7-0892 

268 

•732 

1     2     9-2138 

312 

•688 

1     6     6-0698 

267 

•733 

1     2     8-1943 

311 

•689 

1     6     5-0503 

266 

•234 

1     2     7-1749 

310 

•690 

1     6     4-0309 

265 

•735 

1     2     6-1554 

309 

•691 

1     6     3-0114 

264 

•736 

1     2     5-1351 

308 

•692 

1     6     1-9919 

263 

•737 

1     2     4-1165 

307 

•693 

1     6     0-9725 

262 

•738 

1     2     3-0970 

306 

•694 

1     5  11-9530 

261 

•739 

1     2     2-0776 

305 

•695 

1     5  10-9336 

260 

•740 

1     2     1-0581 

304 

•696 

1     5     9-9141 

259 

•741 

1     2     0-0387 

303 

•697 

1     5     8-8947 

258 

•742 

1     1   11-0192 

302 

•698 

1     5     7-8752 

257 

•743 

1     1     9-9998 

XXX 


GOLD-VALUING   TABLE. 


FINE 
GOLD 

AlXOY 

VALUE 

FINE 
GOLD 

ALLOY 

VALUE 

£   s.   d. 

£   s.   d. 

256 

-744 

1     8-9803 

211 

•789 

0  17  11-1049 

255 

•745 

1     7-9609 

210 

•790 

0  17  10-0854 

254 

•746 

1     6-9414 

209 

•791 

0  17  9-0659 

253 

•747 

1     5-9219 

208 

•792 

0  17  8-0465 

252 

•748 

1     4-9025 

207 

•793 

0  17  7-0270 

251 

•749 

1     3-8830 

206 

•794 

0  17  6-0076 

250 

•750 

1     2-8636 

205 

•795 

0  17  4-9881 

249 

•751 

1     1-8441 

204 

•796 

0  17  3-9687 

248 

•752 

1  1  0-8247 

203 

•797 

0  17  2-9492 

247 

•753 

1  0  11-8052 

202 

•798 

0  17  1-9298 

246 

•754 

1  0  10-7858 

201 

•799 

0  17  0-9103 

245 

•755 

1  0  9-7663 

200 

•800 

0  16  11-8909 

244 

•756 

1  0  8-7469 

199 

•801 

0  16  10-8714 

243 

•757 

1  0  7-7274 

198 

•802 

0  16  9-8519 

242 

•758 

1  0  6-7079 

197 

•803 

0  16  8-8325 

241 

•759 

1  0  5-6885 

196 

•804 

0  16  7-8130 

240 

•760 

1  0  4-6690 

195 

•805 

0  16  6-7936 

239 

•761 

1  0  3-6496 

194 

•806 

0  16  5-7741 

238 

•762 

1  0  2-6301 

193 

•807 

0  16  4-7547 

237 

•763 

1  0  1-6107 

192 

•808 

0  16  3-7352 

236 

•764 

1  0  0-5912 

191 

•809 

0  16  2-7158 

235 

•765 

0  19  11-5718 

190 

•810 

0  16  1-6963 

234 

•766 

0  19  10-5523 

189 

•811 

0  16  0-6769 

233 

•767 

0  19  9-5329 

188 

•812 

0  15  11-6574 

232 

•768 

0  19  8-5134 

187 

•813 

0  15  10-6379 

231 

•769 

0  19  7-4939 

186 

-814 

0  15  9-6185 

230 

•770 

0  19  6-4745 

185 

•815 

0  15  8-5990 

229 

•771 

0  19  5-4551 

184 

•816 

0  15  7-5796 

228 

•772 

0  19  4-4356 

183 

•817 

0  15  6-5601 

227 

•773 

0  19  3-4161 

182 

•818 

0  15  5-5407 

226 

•774 

0  19  2-3967 

181 

•819 

0  15  4-5212 

225 

•775 

0  19  1-3772 

180 

•820 

0  15  3-5018 

224 

•776 

0  19  0-3578 

179 

•821 

0  15  2-4823 

223 

•777 

0  18  11-3383 

178 

•822 

0  15  1-4629 

222 

•778 

0  18  10-3189 

177 

•823 

0  15  0-4434 

221 

•779 

0  18  9-2994 

176 

•824 

0  14  11-4239 

220 

•780 

0  18  8-2799 

175 

•825 

0  14  10-4045 

219 

•781 

0  18  7-2605 

174 

•826 

0  14  9-3851 

218 

•782 

0  18  6-2410 

173 

•827 

0  14  8-3656 

217 

•783 

0  18  5-2216 

172 

•828 

0  14  7-3461 

216 

•784 

0  18  4-2021 

171 

•829 

0  14  6-3267 

215 

•785 

0  18  3-1827 

170 

•830 

0  14  5-3072 

214 

•786 

0  18  2-1632 

169 

•831 

0  14  4-2878 

213 

•787 

0  18  1-1438 

168 

•832 

0  14  3-2683 

212 

•788 

0  18  0-1243 

167 

•833 

0  14  2-2489 

GOLD-VALUIXG   TABLE. 


XXXI 


FINE 

GOLD 

ALLOY 

VALUB 

FIXE 
GOLD 

ALLOT 

VALUE 

£   8.   d. 

£  *.  d. 

166 

•834 

0  14  1-2294 

121 

•879 

0  10  3-3530 

165 

•835 

0  14  0-2099 

120 

•880 

0  10  2-3345 

164 

•836 

0  13  11-1905 

119 

•881 

0  10  1-3151 

163 

•837 

0  13  10-1710 

118 

•882 

0  10  0-2956 

162 

•838 

0  13  9-1516 

117 

•883 

0  9  11-2761 

161 

•839 

0  13  8-1321 

116 

•884 

0  9  10-2567 

160 

•840 

0  13  7-1127 

115 

•885 

0  9  9-2372 

159 

•841 

0  13  6-0932 

114 

•886 

0  9  8-2178 

158 

•842 

0  13  5-0738 

113 

•887 

0  9  7-1983 

157 

•843 

0  13  4-0543 

112 

•888 

0  9  6-1789 

156 

•844 

0  13  3-0349 

111 

•889 

0  9  5-1594 

155 

•845 

0  13  2-0154 

110 

•890 

0  9  4-1399 

154 

•846 

0  13  0-9959 

109 

•891 

0  9  3-1205 

153 

•847 

0  12  11-9765 

108 

•892 

0  9  2-1010 

152 

•848 

0  12  10-9570 

107 

•893 

0  9  1-0816 

151 

•849 

0  12  9-9376 

106 

•894 

0  9  0-0621 

150 

•850 

0  12  8-9181 

105 

•895 

0  8  11-0427 

149 

•851 

0  12  7-8987 

104 

•896 

0  8  10-0232 

148 

•852 

0  12  6-8792 

103 

•897 

0  8  9-0038 

147 

•853 

0  12  5-8598 

102 

•898 

0  8  7-9843 

146 

•854 

0  12  4-8403 

101 

•899 

0  8  6-9649 

145 

•855' 

0  12  3-8209 

100 

•900 

0  8  5-9454 

144 

•856 

0  12  2-8014 

99 

-901 

0  8  4-9259 

143 

•857 

0  12  1-7819 

98 

•902 

0  8  3-9065 

142 

•858 

0  12  0-7625 

97 

•903 

0  8  2-8870 

141 

•859 

0  11  11-7430 

96 

•904 

0  8  1-8676 

140 

•860 

0  11  10-7236 

95 

•905 

0  8  0-8481 

139 

•861 

0  11  9-7041 

94 

•906 

0  7  11-8287 

138 

•862 

0  11  8-6847 

93 

•907 

0  7  10-8092 

137 

•863 

0  11  7-6652 

92 

•908 

0  7  9-7898 

136 

•864 

0  11  6-6458 

91 

•909 

0  7  8-7703 

135 

•865 

0  11  5-6263 

90 

•910 

0  7  7-7509 

134 

•866 

0  11  4-6069 

89 

•911 

0  7  6-7314 

133 

•867 

0  11  3-5874 

88 

•912 

0  7  5-7119 

132 

•868 

0  11  2-5679 

87 

•913 

0  7  4-6925 

131 

•869 

0  11  1-5485 

86 

•914 

0  7  3-6730 

130 

•870 

0  11  0-5290 

85 

•915 

0  7  2-6536 

129 

•871 

0  10  11-5096 

84 

•916 

0  7  1-6341 

128 

•872 

0  10  10-4901 

83 

•917 

0  7  0-6147 

127 

•873 

0  10  9-4707 

82 

•918 

0  6  11-5952 

126 

•874 

0  10  8-4512 

81 

•919 

0  6  10-5758 

125 

•875 

0  10  7-4318 

80 

•920 

0  6  9-5563 

124 

•876 

0  10  6-4123 

79 

•921 

0  6  8-5369 

123 

•877 

0  10  5-3929 

78 

•722 

0  6  7-5174 

122 

•«78 

0  10  4-3734 

!  77 

•923 

0  6  6-4979 

xxxii 


GOLD-VALUING   TABLE; 


FINE 
GOLD 

ALLOY 

VALUE 

FINE 
GOLD 

ALLOY 

VALUE 

'£     s.     d. 

gj 

£     s.     d. 

76 

•924 

0     6     5-4785 

38 

•962 

0     3     2-7392 

75 

•925 

0     6     4-4590 

37 

•963 

0     3     1-7198 

74 

•926 

0     6     3-4396 

36 

•964 

0     3     0-7003 

73 

•927 

0     6     2-4201 

35 

•965 

0     2  11-6809 

72 

•928 

0     6     1-4007 

34 

•966 

0     2  10-6614 

71 

•929 

0     6     0-3812 

33 

•967 

0     2     9-6419 

70 

•930 

0     5  11-3618 

32 

•968 

0     2     8-6225 

69 

•931 

0     5  10-3423 

31 

•969 

0     2     7-6030 

68 

•932 

0     5     9-3229 

30 

•970 

0     2     6-5836 

67 

•933 

0     5     8-3034 

29 

•971 

0     2     5-5641 

66 

•934 

0     5     7-2839 

28 

•972 

0     2     4-5447 

65 

•935 

0     5     6-2645 

27 

•973 

0     2     3-5252 

64 

•936 

0     5     5-2451 

26 

•974 

0     2     2-5058 

63 

•937 

0     5     4-2256 

25 

•975 

0     2     1-4863 

62 

•938 

0     5     3-2061 

24 

•976 

0     2     0-4669 

61 

•939 

0     5     2-1867 

23 

•977 

0     1   11-4474 

60 

•940 

0     5     1-1672 

22 

•978 

0     1   10-4279 

59 

•941 

0     5     0-1478 

21 

•979 

0     1     9-4085 

58 

•942 

0     4  11-1283 

20 

•980 

0     1     8-3890 

57 

•943 

0     4  10-1089 

19 

•981 

0     1     7-3696 

56 

•944 

0     4     9-0894 

18 

•982 

0     1     6-3501 

55 

•945 

0     4     8-0699 

17 

•983 

0     1     5-3307 

54 

•946 

0     4     7-0505 

16 

•984 

0     1     4-3112 

53 

•947 

0     4     6-0310 

15 

•985 

0     1     3-2918 

52 

•948 

0     4     5-0116 

14 

•986 

0     1     2-2723 

51 

•949 

0     4     3-9921 

13 

•987 

0     1     1-2529 

50 

•950 

0     4     2-9727 

12 

•988 

0     1     0-2334 

49 

•951 

0     4     1-9532 

11 

•989 

0     0  11-2139 

48 

•952 

0     4     0-9338 

10 

•990 

0     0  10-1945 

47 

•953 

0     3  11-9143 

9 

•991 

0     0     9-1750 

46 

•954 

0     3  10-8949 

8 

•992 

0     0     8-1556 

45 

•955 

0     3     9-8754 

7 

•993 

0     0     7-1361 

44 

•956 

0     3     8-8559 

6 

•994 

0     0     6-1167 

43 

•957 

0     3     7-8365 

5 

•995 

0     0     5-0972 

42 

•958 

0     3     6-8170 

4 

•996 

0     0     4-0778 

41 

•959 

0     3     5-7976 

3 

•997 

0     0     3-0583 

40 

•960 

0     3     4-7781 

2 

•998 

0     0     2-0389 

39 

•961 

0     3     3-7587 

1 

•999 

0     0     1-0194 

GOLDrVALffim  TABLE. 


XXX111 


To  convert  MINT  VALUE  into  BANK  VALUE  when  the  Standard  is 
expressed  in  Thousandths. 


Thousandths 

Value  in  Pence 

Thousandths 

Value  in  Pence 

1 

•001636 

6 

•009816 

2 

•003272 

7 

•011352 

3 

•004908 

8 

•013088 

4 

.     -006544 

9 

•014724 

5 

•008180 

,;-.:.;•:. 

.. 

To  illustrate  the  use  of  the  above  table,  gold  of  ^°^ths  fine 
may  be  taken.  As  in  the  Table  for  finding  the  Bank  value  of 
gold  when  the  standard  is  reported  in  carats,  &c.,  the  amounts 
in  pence,  as  above,  are  to  be  deducted  from  the  prices  attached 
to  corresponding  standards  in  Table  No.  2.  Thus,  the  minus 
value  of  T-^-^ths  is  '00818  of  a  penny  ;  therefore,  the  minus  value 
of  T5_o_o_ths  is  *818  of  a  penny,  which  amount  must  be  deducted 
from  the  Mint  price  of  gold  at  the  above  standard.  On  refer- 
ring to  the  Table  it  will  be  found  to  be  £2  2s.  5'7272c£.  per  oz. 
Now,  if  -818  be  deducted,  the  remainder  will  be  £2  2s.  4-9092d., 
representing  the  Bank  value  of  1  oz.  of  gold  of  the  fineness  just 
mentioned. 


XXXIV 


ASSAY    TABLE. 


TABLE   III. 


ASSAY  TABLE,  showing  the  Amount  of  GOLD  or  SILVER,  in  Ounces, 
Pennyweights,  and  Grains,  contained  in  a  Ton  of  Ore,  &c. 
from  the  Weight  of  Metal  obtained  in  an  Assay  of  200  Grains 
of  Mineral. 


If  200  Grains  of 

One  Ton  of  Ore 

If  200  Grains  of 

One  Ton  of  Ore 

Ore  give  of 

will  yield  of 

Ore  give  of 

will  yield  of 

FINE  METAL 

FINE  METAL 

FINE  METAL 

FINE  METAL 

Gr. 

Oz.   Dwts.    Grs. 

Gr. 

Oz.   Dwts.    Grs. 

•001 

036 

•031 

516. 

•002 

0       6     12 

•032 

5       4     12 

•003 

0       9     19 

•033 

5       7     19 

•004 

0     13       1 

•034 

5     11       1 

•005 

0     16       8 

•035 

5     14       8 

•006 

0     19     14 

•036 

5     17     14 

•007 

1       2     20 

•037 

6       0     20 

•008 

1       6       3 

•038 

643 

•009 

1       9       9 

•039 

679 

•010 

1     12       6 

•040 

6     10     16 

•Oil 

1     15     22 

•041 

6     13     22 

•012      . 

1     19       4 

•042 

6     17       4 

•013 

2211 

•043 

7       0     11 

•014 

2       5     17 

•044 

7       3     17 

•015 

290 

•045 

770 

•016 

2     12       6 

•046 

7     10       6 

•017 

2     15     12 

•047 

7     13     12 

•018 

2     18     19 

•048 

7     16     19 

•019 

321 

•049 

8       0       1 

•020 

358 

•050 

838 

•021 

3       8     14 

•051 

8       6     14 

•022 

3     11     20 

•052 

8       9     20 

•023 

3     15       3 

•053 

8     13       3 

•024 

3     18       9 

•054 

8     16       9 

•025 

4       1     16 

•055 

8     19     16 

•026 

4       4     22 

•056 

9       2     22 

•027 

484 

•057 

964 

•028 

4     11     11 

•058 

9       9     11 

•029 

4     14     17 

•059 

9     12     17 

•030 

4     18       0 

•060 

9     16       0 

ASSAY   TABLE. 


XXXV 


If  200  Grains  of 

One  Ton  of  Ore 

If  200  Grains  of 

One  Ton  of  Ore 

Ore  give  of 

•will  yield  of 

Ore  give  of 

•will  yield  of 

FINE  METAL 

FIXE  METAL 

FINE  METAL 

FINE  MBTAL 

Gr. 

Oz.    Dwts.    Grs. 

Gr. 

Oz.    Dwts.    Grs. 

•061 

9      19         6 

•105 

17       3       0 

•062 

10       2     12 

•106 

17       6       6 

•063 

10       5     19 

•107 

17       9     12 

•064 

10       9       1 

•108 

17     12     19 

•065 

10     12       8 

•109 

17     16       1 

•066 

10     15     14 

•110 

17     19       8 

•067 

10     18     20 

•111 

18       2     14 

•068 

11       2       3 

•112 

18       5     20 

•069 

11       5       9 

•113 

18       9       3 

•070 

11       8     16 

•114 

18     12       9 

•071 

11     11     22 

•115 

18     15     16 

•072 

11     15       4 

•116 

18     18     22 

•073 

11     18     11 

•117 

19       2       4 

•074 

12       1     17 

•118 

19       5     11 

•075 

12       5       0 

•119 

19       8     17 

•076 

12       8       6 

•120 

19     12       0 

•077 

12     11     12 

•121 

19     15       6 

•078 

12     14     19 

•122 

19     18     12 

•079 

12     18       1 

•123 

20       1     19 

•080 

13       1       8 

•124 

20       5       1 

•081 

13       4     14 

•125 

20       8       8 

•082 

13       7     20 

•126 

20     11     14 

•083 

13     11       3 

•127 

20     14     20 

•084 

13     14       9 

•128 

20     18       3 

•085 

13     17     16 

•129 

21       1       9 

•086 

14       0     22 

•130 

21       4     16 

•087 

14       4       4 

•131 

21       7     22 

•088 

14       7     11 

•132 

21     11       4 

•089 

14     10     17 

•133 

21     14     11 

•090 

14     14       0 

•134 

21     17     17 

•091 

14     17       6 

•135 

22       1       0 

•092 

15       0     12 

•136 

22       4       6 

•093 

15       3     19 

•137 

22       7     12 

•094 

15       7       1 

•138 

22     10     19 

•095 

15     10       8 

•139 

22     14       1 

•096 

15     13     14 

•140 

22     17       8 

•097 

15     16     20 

•141 

23       0     14 

•098 

16       0       3 

•142 

23       3     20 

•099 

16       3       9 

•143 

23       7       3 

•100 

16       6     16 

•144 

23     10       9 

•101 

16       9     22 

•145 

23     13     16 

•102 

16     13       4 

•146 

23     16     22 

•103 

16     16     11 

•147 

24       0       4 

•104 

16     19     17 

•148 

24       3     11 

XXXVI 


ASSAY   TABLE. 


If  200  Grains  of 

One  Ton  of  Ore 

If  200  Grains  of 

One  Ton  of  Ore 

Ore  give  of 

will  yield  of 

Ore  give  of 

will  yield  of 

FINE  METAL 

FINE  METAL 

FINE  METAL 

FINE  METAL 

>  Gr. 

Oz.    Dwts.  Grs. 

Gr. 

,Oe.     Dwts.,  Grs. 

•149 

24       6     17 

•193 

31       10      11 

•150 

24     10       0 

•194 

31      13     17 

•151 

24     13       6 

•195 

31     17       0 

•152 

24     16     12 

•196 

32       0       6 

•153 

24     19     19 

•197 

32       3     12 

•154 

25       3       1 

•198 

32       6     19 

•155 

25       6       8 

•199 

32     10       1 

•156 

25       9     14 

•200 

32     13       8 

•157 

25     12     20 

•201 

32     16     14 

•158 

25     16       3 

•202 

32     19     20 

•159 

25     19       9 

•203 

33       3       3 

•160 

26       2     16 

•204 

33       6       9 

•161 

26       5     22 

•205 

33       9     16 

•162 

26       9       4 

•206 

33     12     22 

•163 

26     12     11 

•207 

33     16       4 

•164 

26     15     17 

•208 

33     19     11 

•165 

26     19       0 

•209 

34       2     17 

•166 

27       2       6 

•210 

34       6       0 

•167 

27       5     12 

•211 

34       9       6 

•168 

27       8     19 

•212 

34     12     12 

•169 

27     12       1. 

•213 

34     15     19 

•170 

27     15       8 

•214 

34     19       1 

•171 

27     18     14 

•215 

35       2       8 

•172 

28       1     20 

•216 

35       5     14 

•173 

28       5       3 

•217 

35       8     20 

•174 

28       8       9 

•218 

35     12       3 

•175 

28     11     16 

•219 

35     15       9 

•176 

28     14     22 

•220 

35     18     16 

•177 

28     18       4 

•221 

36       1     22 

•178 

29       1     11 

•222 

36       5       4 

•179 

29       4     17 

•223 

36       8     11 

•180 

29       8       0 

•224 

36     11     17 

•181 

29     11       6 

•225 

36     15       0 

•182 

29     14     12 

•226 

36     18       6 

•183 

29     17     19 

•227 

37       1     12 

•184 

30       1       1 

•228 

37       4     19 

•185 

30       4       8 

•229 

37       8       1 

•186 

30       7     14 

•230 

37     11       8 

•187 

30     10     20 

•231 

37     14     14 

•188 

30     14       3 

•232 

37     17     20 

•189 

30     17       9 

•233 

38       1       3 

•190 

31       0     16 

•234 

38       4       9 

•191 

31       3     22 

•235 

38       7     16 

•192 

31       7       4 

'236 

38     10     22 

.ASSAY   TABLE. 


XXXV.ll 


If  200  Grains  of 

One  Ton  of  Ore 

If  200  Grains  of 

One 

Ton  of  Ore 

Ore  give  of 

will  yield 

of 

Ore  give  of 

Wl 

11  yield 

of 

FINE  METAL 

FINE  METAL           ;  - 

FINE  METAL 

FINE  METAL 

Gr. 

Oz. 

Dwts. 

,Grs. 

Gr. 

0*. 

Dwts. 

Grs. 

•237 

38 

14 

4 

•281 

45 

17 

22 

•238 

38 

17 

11 

•282 

46 

1 

4 

•239 

39 

0 

17 

•283 

46 

4 

11 

•240 

39 

4 

0 

•284 

46 

7 

17 

•241 

39 

7 

6 

•285 

46 

11 

0 

•242 

39 

10 

12 

•286 

46 

14 

6 

.      -243 

39 

13 

18 

•287 

46 

17 

12 

•244 

39 

17 

1 

•288 

47 

0 

19 

•245 

40 

0 

8 

•289 

47 

4 

1 

•246 

40 

3 

14 

•290 

47 

7 

8 

•247 

40 

6 

20 

•291 

47 

10 

14 

•248 

40 

10 

3 

•292 

47 

13 

20 

•249 

40 

13 

9 

•293 

47 

17 

3 

•250 

40 

16 

16 

•294 

48 

0 

9 

•251 

40 

19 

22 

•295 

48 

3 

16 

•252 

41 

3 

4 

•296 

48 

6 

22 

•253 

41 

6 

11 

•297 

48 

10 

4 

•254 

41 

9 

17 

•298 

48 

13 

11 

•255 

41 

13 

0 

•299 

48 

16 

17 

•256 

41 

16 

6 

•300 

49 

0 

0 

•257 

41 

19 

12 

•301 

49 

3 

6 

•258 

42 

2 

19 

•302 

49 

6 

12 

•259 

42 

6 

1 

•303 

49 

9 

19 

•260 

42 

9 

8 

•304 

49 

13 

1 

•261 

42 

12 

14 

•305 

49 

16 

8 

•262 

42 

15 

20 

•306 

49 

19 

14 

•263 

42 

19 

3 

•307 

50 

2 

20 

•264 

43 

2 

9 

•308 

50 

6 

3 

•265 

43 

5 

16 

•309 

50 

9 

9 

•266 

43 

8 

22 

•310 

50 

12 

16 

•267 

43 

12 

4 

•311 

50 

15 

22 

•268 

43 

15 

11 

•312 

50 

19 

4 

•269 

43 

18 

17 

•313 

51 

2 

11 

•270 

44 

2 

0 

•314 

51 

5 

17 

•271 

44 

5 

6 

•315 

51 

9 

0 

•272 

44 

8 

12 

•316 

51 

12 

6 

•273 

44 

11 

19 

•317 

51 

15 

12 

•274 

44 

15 

1 

•318 

51 

18 

19 

•275 

44 

18 

8 

•319 

52 

2 

1 

•276 

45 

1 

14 

•320 

52 

5 

8 

•277 

45 

4 

20 

•321 

52 

8 

14 

•278 

45 

8 

3 

•322 

52 

11 

20 

•279 

45 

11 

9 

•323 

52 

15 

3 

•280 

45 

14 

16 

•324 

52 

18 

9 

XXXV111 


ASSAY   TABLE. 


If  200  Grains  of 

One  Ton  of  Ore 

If  200  Grains  of 

One  Ton  of  Ore 

Ore  give  of 

will  yield  of 

Ore  give  of 

will  yield  of 

FINE  METAL 

FINE  METAL 

FINE  METAL 

FINE  METAL 

Gr. 

Oz.    Dwts.  Grs. 

Gr. 

Oz.    Dwts.  Grs. 

•325 

53         1      16 

•369 

60         5         9 

•326 

53       4     22 

•370 

60       8     16 

•327 

53       8       4 

•371 

60     11     22 

•328 

53     11     11 

•372 

60     15       4 

•329 

53     14     17 

•373 

60     18     11 

•330 

53     18       0 

•374 

€1       1     17 

•331 

54       1       6 

•375 

61       5       0 

•332 

54       4     12 

•376 

61       8       6 

•333 

54       7     19 

•377 

61     11     12 

•334 

54     11       1 

•378 

61     14     19 

•335 

54     14       8 

•379 

61     18       1 

•336 

54     17     14 

•380 

62       1       8 

•337 

55       0     20 

•381 

62       4     14 

•338 

55       4       3 

•382 

62       7     20 

•339 

55       7       9 

•383 

62     11       3 

•340 

55     10     16 

•384 

62     14       9 

•341 

55     13     22 

•385 

62     17     16 

•342 

55     17       4 

•386 

63       0     22 

•343 

56       0     11 

•387 

63       4       4 

•344 

56       3     17 

•388 

63       7     11 

•345 

56       7       0 

•389 

63     10     17 

•346 

56     10       6 

•390 

63     14       0 

•347 

56     13     12 

•391 

63     17       6 

•348 

56     16     19 

•392 

64       0     12 

•349 

57       0       1 

•393 

64       3     19 

•350 

57       3       8 

•394 

64       7       1 

•351 

57       6     14 

•395 

64     10       8 

•352 

57       9     20 

•396 

64     13     14 

•353 

57     13       3 

•397 

64     16     20 

•354 

57     16       9 

•398 

65       0       3 

•355 

57     19     16 

•399 

65       3       9 

•356 

58       2     22 

•400 

65       6     16 

•357 

58       6       4 

•401 

65       9     22 

•358 

58       9     11 

•402 

65     13       4 

•359 

58     12     17 

•403 

65     16     11 

•360 

58     16       0 

•404 

65     19     17 

•361 

58     19       6 

•405 

66       3       0 

•362 

59       9     12 

•406 

66       6       6 

•363 

59       5     19 

•407 

66       9     12 

•364 

59       9       1 

•408 

66     12     19 

•365 

59     12       8 

•409 

66     16       1 

•366 

59     15     14 

•410 

66     19       8 

•367 

59     18     20 

•411 

67       2     14 

•368 

60       2       3 

•412 

67       5     20 

ASSAY    TABLE. 


XXXIX 


If  200  Grains  of 

One  Ton  of  Ore 

If  200  Grains  of 

One  Ton  of  Ore 

Ore  give  of 

will  yield  of 

Ore  give  of 

will  yield  o. 

FINE  METAL 

FINE  METAL 

FINE  METAL 

FINE  METAL 

Gr. 

Qz.     Dwfs.  Grs. 

Gr. 

Oz.     Dwts.  Grs. 

•413 

67       9       3 

•457 

74      12      20 

•414 

67     12       9 

•458 

74     16       3 

•415 

67     15     16 

•459 

74     19       9 

•416 

67     18     22 

•460 

75       2     16 

•417 

68       2       4 

•461 

75       5     22 

•418 

68       5     11 

•462 

75       9       4 

•419 

68       8     17 

•463 

75     12     11 

•420 

68     12       0 

•464 

75     15     17 

•421 

68     15       6 

•465 

75     19       0 

•422 

68     18     12« 

•466 

76       2       6 

•423 

69       1     19 

•467 

76       5     12 

•424 

69       5       1 

•468 

76       8     19 

•425 

69       8       8 

•469 

76     12       1 

•426 

69     11     14 

•470 

76     15       8 

•427 

69     14     20 

•471 

76     18     14 

•428 

69     18       3 

•470 

77       1     20 

•429 

70       1       9 

•473 

77       5       3 

•430 

70       4     16 

•474 

77       8       9 

•431 

70       7     22 

•475 

77     11     16 

•432 

70     11       4 

•476 

77     14     22 

•433 

70     14     11 

•477 

77     18       4 

•434 

70     17     17 

•478 

78       1     11 

•435 

71       1       0 

•479 

78       4     17 

•436 

71       4       6 

-480 

78       8       0 

•437 

71       7     12 

•481 

78     11        6 

•438 

71     10     19 

•482 

78     14     12 

•439 

71     14       1 

•483 

78     17     19 

•440 

71     17       8 

•484 

79       1       1 

•441 

72       0     14 

•485 

79       4       8 

•442 

72       3     20 

•486 

79       7     14 

•443 

72       7       3 

•487 

79     10     20 

•444 

72     10       9 

•488 

79     14       3 

•445 

72      13     16 

•489 

79     17       9 

•446 

72     16     22 

•490 

80       0     16 

•447 

73       0       4 

•491 

80       3     22 

•448 

73       3     11 

•492 

80       7       4 

•449 

73       6     17' 

•493 

80     10     11 

•450 

73     10       0 

•494 

80     13     17 

•451 

73     13       6 

•495 

80     17       0 

•452 

73     16     12 

•496 

81       06 

•453 

73     19     19 

•497 

81       3     12 

•454 

74       3       1 

•498 

81       6     19 

•455 

74       6       8 

•499 

81     10       1 

•456 

74       9     14 

•500 

81      13       8 

31 


xl 


ASSAY    TABLE. 


If  200  Grains  of 

One  Ton  of  Ore 

If  200  Grains  of 

One  Ton  of  Ore 

Ore  give  of 

will  yield  of 

Ore  give  of 

will  yield  of 

FINE  METAL 

FINE  METAL 

FINE  METAL 

FINE  METAL 

Gr. 

Oz.     Dwts.   Grs. 

Gr. 

0;.     Dwts.   Grs. 

•501 

81      16     14 

•545 

89         0         8 

•502 

81      19     20 

•546 

89       3     14 

•503 

82       3       3 

•547 

89       6     20 

•504 

82       6       9 

•548 

89     10       3 

•505 

82       9     16 

•549 

89     13       9 

•506 

82     12     22 

•550 

89     16     16 

•507 

82     16       4 

•551 

89     19     22 

•5C8 

82     19     11 

•552 

90       3       4 

•509 

83       2     17 

•553 

90       6     11 

•510 

83       6       0 

•554 

90       9     17 

•511 

83       9       6 

•555 

90     13       0 

•512 

83     12     12 

•556 

90     16       6 

•513 

83     15     19 

•557 

90     19     12 

•514 

83     19       1 

•558 

91        2     19 

•515 

84       2       8 

•559 

91        6       1 

•516 

84       5     14 

•560 

91        9       8 

•517 

84       8     20 

•561 

91      12     14 

•518 

84     12        3 

•562 

91      15     20 

•519 

84     15       9 

•563 

91      19       3 

•520 

84     18     16 

•564 

9'>,       2       9 

•521 

85        1      22 

•565 

92       5     16 

•522 

85       5       4 

•566 

92       8     22 

•523 

85       8     11 

•567 

92     12       4 

•524 

85      11      17 

•5(58 

92     15     11 

•525 

85     15       0 

•5()9 

92     18     17 

•526 

85     18       6 

•570 

93       2       0 

•527 

86       1      12 

•571 

93       5       6 

•528 

86       4     19 

•572 

93       8      12 

•529 

86       8        1 

•573 

93     11      19 

•530 

86      11       8 

•574 

93     15       1 

•531 

86     14     14 

•575 

93     18        8 

•532 

86     17     20 

•576 

94       1      14 

•533 

87        1        3 

•577 

94       4     20 

•534 

87       4       9 

•578 

94       8       3 

•535 

87       7     16 

•579 

94     11        9 

•536 

87     10     22 

•580 

94     14     16 

•537 

87      14       4 

•581 

94     17     22 

•538 

87      17      11 

•582 

95        1        4 

•539 

88       0     17 

•533 

95       4     11 

•540 

88       4       0 

•584 

95       7     17 

•541 

88       7       6 

•585 

95     11       0 

•542 

88     10     12 

•586 

95     14       6 

•543 

88      13     19 

•587 

95     17     12 

•544 

88     17        1 

•588 

96       0     19 

ASSAY   TABLE. 


xli 


If  200  Grains 

cf    One  Ton  of  Ore 

If  200  Grains 

of    One  Ton  of  Ore 

Ore  give  of 

will  yield  of 

Ore  give  of 

will  yield  of 

FINE  METAL 

FINE  METAL 

FINE  METAL 

FINE  METAL 

Gr. 

Oz.     Dwts.  Grs. 

Gr. 

Oz.     Dwts.   Grs. 

•589 

96        4         1 

•633 

103       7     19 

•590 

96       7       8 

•634 

103     11        I 

•591  • 

96     10     14 

•635 

103     14       8 

•592 

96     13     20 

•636 

103     17     14 

•593 

96     17       3 

•637 

104       0     20 

•594 

97       0       9 

•638 

104       4       3 

•595 

97       3     16 

•639 

104       7       9 

•596 

97       6     22 

•640 

104     10     16 

•597 

97     10       4 

•641 

104     13     22 

•598' 

97     13     11 

•642 

104     17       4 

•599 

97     16     17 

•643 

105       0     11 

•COO 

98       0       0 

•644 

105       3     17 

•601 

98       3       6 

•645 

105       7       0 

•602 

98       6     12 

•646 

105     10       6 

•603 

98       9     19 

•647 

105     13     12 

•604 

98     13       1 

•648 

105     16     19 

•605 

98     16       8 

•649 

106       0       1 

•606 

98     19     14 

•650 

106       3       8 

•e;o7 

99       2     20 

•6ol 

106       6     14 

•608 

99       6       3 

•052 

106       9     20 

•609 

99       9       9 

•653 

106     13       3 

•610 

99     12     16 

•654 

106     16       9 

•till 

99     15     22 

•655 

106     19     16 

•012 

99     19       4 

•656 

107       2     22 

•613 

100       2     11 

•657 

107       6       4 

•614 

100       5     17 

•C.58 

107       9     11 

•615 

100       9       0 

•659 

107     12     17 

•616 

100     12       6 

•660 

107     16       0 

•617 

100     15     12 

•661 

107     19       6 

•618 

100     18     19 

•662 

108       2     12 

•(519 

101       2       1 

•663 

108       5     19 

•620 

101       5       8 

•G64 

108       9       1 

•621 

101       8     14 

•665 

108     12       8 

•622 

101      11     20 

•666 

108     15     14 

•623 

101      15       3 

•667 

108     18     20 

•624 

101      18       9 

•u68 

109       2       3 

•625 

102       1      16 

•669 

109       5       9 

•626 

102       4     22 

•670 

109       8     16 

•627 

102       8       4 

•671 

109     11     22 

•628 

102      11      11 

•672 

109     15       4 

•629 

102     14     17 

•673 

109     18     11 

•630 

102     18       0 

•674 

110       1      17 

•631 

103       1       6 

•675 

110       5       0 

•632 

103       4     12 

•676 

110       8       6 

312 


xlii 


ASSAY   TABLE. 


If  200  Grains  of 

One  Ton  of  Ore 

If  200  Grains 

of    One  Ton  of  Ore 

Ore  give  of 

will  yield  of 

Ore  give  of 

will  yield  of 

FINE  METAL 

FINE  METAL 

FIXE  METAL 

FINE  METAL 

Gr. 

Oz.     Dwts.  Grs. 

Gr. 

Oz.     Dwts.  Grs. 

•677 

110      11       12 

•721 

117     15       6 

•678 

110      14      19 

•722 

117     18     12 

•679 

110      18         1 

•723 

118       1     19 

•680 

111        1       8 

•724 

118       5       1 

•681 

111       4     14 

•725 

118       8       8 

•682 

111       7     20 

•726 

118     11     14 

•683 

111     11       3 

•727 

118     14     20 

•684 

111     14       9 

•728 

118     18       3 

•685 

111     17       6 

•729 

119       1        9 

•686 

112       0     22 

•730 

119       4     16 

•687 

112       4       4 

•731 

119       7     22 

•688 

112       7     11 

•732 

119     11       4 

-689 

112     10     17 

•733 

119     14     11 

•690 

112     14       0 

•734 

119     17     17 

•  -691 

112     17       6 

•735 

120       1       0 

•692 

113       0     12 

•736 

120       4       6 

•693 

113       3     19 

•737 

120       7     12 

•694 

113       7       1 

•738 

120     10     19 

•695 

113     10       8 

•739 

120     14       1 

•696 

113     13     14 

•740 

120     17       2 

•697 

113     16     20 

•741 

121       0     14 

•698 

114       0       3 

•742 

121        3     20 

•699 

114       3       9 

•743 

121       7       3 

•700 

114       6     16 

•744 

121      10       9 

•701 

114       9     22 

•745 

121     13       6 

•702 

114     13       4 

•746 

121     16     22 

•703 

114     16     12 

•747 

122       0       4 

•704 

114     19     17 

•748 

122       3     11 

•705 

115       3       0 

•749 

122       6     17 

*  -706 

115       6       6 

•750 

122     10       0 

•707 

115       9     12 

•751 

122     13     16 

•708 

115     12     19 

•752 

122     16     12 

•709 

115     16       1 

•753 

122     19     19 

•710 

115     19       8 

•754 

123       3       1 

•711 

116       2     14 

•755 

123       6       8 

•712 

116       5     20 

•756 

123       9     14 

•713 

116       9       3 

•757 

123     12     20. 

•714 

116     12       9 

•758 

123     16       3 

•715 

116     15     16 

•759 

123     19       9 

•716 

116     18     22 

•760 

124       2     16 

•717 

117       2       4 

•761 

124       5     22 

•718 

117       5     11 

•762 

124       9       4 

•719 

117       8     17 

•763 

124     12     11 

•720 

117     12       0 

•764 

124     15     17 

ASSAY   TABLE. 


xliii 


If  200  Grains  of 

One  Ton  of  Ore 

If  200  Grains  of 

One  Ton  of  Ore 

Ore  give  of 

will  yield  of 

Ore  give  of 

will  yield  of 

FINE  METAL 

FINE   METAL 

FINE  METAL 

FINE   METAL 

Gr. 

Oz.     Dwts.  Grs. 

Gr. 

Oz.     Dwts.  Grs. 

•765 

124     19       o 

•809 

132       2     17 

•766 

125       2       6 

•810 

132       6       0 

•767 

125       5     12 

•811 

132       9       6 

•768 

125       8     19 

•812 

132     12     12 

•769 

125     12       1 

•813 

132     15     19 

•770 

125     15       8 

•814 

132     19       1 

•771 

125     18     14 

•815 

133       2       8 

•772 

126       1     20 

•816 

133       5     14 

•773 

126       5       3 

•817 

133       8     20 

•774 

126       8       9 

•818 

133     12       3 

•775 

126     11     16 

•819 

133     15       9 

•776 

126     14     22 

•820 

133     18     16 

•777 

126     18       4 

•821 

134       1     22 

•778 

127       1     11 

•822 

134       5       4 

•779 

127       4     17 

•823 

134       8     11 

•780 

127       8       0 

•824 

134     11     17 

•781 

127     11       6 

•825 

134     15       0 

•782 

127     14     12 

•826 

134     18       6 

•783 

127     17     19 

•827 

135       1     12 

•784 

128       1        1 

•828 

135       4     19 

•785 

128       4       8 

•829 

135       8       1 

•786 

128       7     14 

•830 

135     11       8 

•787 

128     10     20 

•831 

135     14     14 

•788 

128     14       3 

•832 

135     11        8 

•789 

128     17       9 

•833 

136       1       3 

•790 

129       0     16 

•834 

136       4       9 

•791 

129       3     22 

•835 

136       7     16 

•792 

129       7       4 

•836 

136     10     22 

•793 

129     10     11 

•837 

136     14       4 

•794 

129     13     17 

•838 

136     17     11 

•795 

129     17       0 

•839 

137       0     17 

•796 

130       0       6 

•840 

137       4       0 

•797 

130       3     12 

•841 

137       7       6 

•798 

130       6     19 

•842 

137     10     12 

•799 

130     10       1 

•843 

137     13     19 

•800 

130     13       8 

•844 

137     17       1 

•801 

130     16     14 

•845 

138       0       8 

•802 

130     19     20 

•846 

138       3     14 

•803 

131       3       3 

•847 

138       6     20 

•804 

131       6       9 

•848 

138     10       3 

•805 

131       9     16 

•849 

138     13     19 

•806 

131      12     22 

•850 

138     16     16 

•807 

131      16       4 

•851 

138     19     22 

•808 

131      19     11 

•852 

139       3       4 

xliv 


ASSAY   TABLE. 


If  200  Grains  of 

One 

Ton  of  Ore 

If  200  Grains  of 

One  Ton  of  Ore 

Ore  give  of 

will  yield  of 

Ore  give  of 

will  yield 

of 

FINE  METAL 

FINE   METAL 

FINE   METAL 

FINE   METAL 

Gr. 

Oz. 

Dwts. 

Grs. 

Gr. 

Oz. 

Dwts 

Grs. 

•853 

139 

6 

11 

•897 

146 

10 

4 

•854 

139 

9 

17 

•898 

146 

13 

11 

•855 

139 

13 

0 

•899 

146 

16 

17 

•856 

139 

16 

6 

•900 

147 

0 

0 

•857 

139 

19 

12 

•901 

147 

3 

6 

•858 

140 

2 

19 

•902 

147 

6 

12 

•859 

140 

6 

1 

•903 

147 

9 

19 

•860 

140 

9 

8 

•904 

147 

13 

1 

•861 

140 

12 

14 

•905 

147 

16 

8 

•862 

140 

15 

20 

•906 

147 

19 

14 

•863 

140 

19 

3 

•907 

148 

2 

2 

•864 

141 

2 

9 

•908 

148 

6 

3 

•865 

141 

5 

16 

•909 

148 

9 

9 

•866 

141 

8 

22 

•910 

148 

12 

16 

•867 

141 

12 

4 

•911 

148 

15 

21 

•868 

141 

15 

11 

•912 

148 

19 

4 

•869 

141 

18 

17 

•913 

149 

2 

11 

•870 

142 

2 

0 

•914 

149 

5 

17 

•871 

142 

5 

6 

•915 

149 

9 

0 

•872 

142 

8 

12 

•916 

149 

12 

6 

•873 

142 

11 

19 

•917 

149 

15 

12 

•874 

142 

15 

1 

•918 

149 

18 

19 

•875 

142 

18 

8 

•919 

15o 

2 

1 

•876 

143 

1 

14 

•920 

150 

5 

8 

•877 

143 

4 

20 

•921 

150 

8 

14 

•878 

143 

8 

3 

•922 

150 

11 

20 

•879 

143 

11 

9 

•923 

150 

15 

3 

•880 

143 

14 

16 

•924 

150 

18 

9 

•881 

143 

17 

22 

•925 

151 

1 

16 

•882 

144 

1 

4 

•926 

151 

4 

22 

•883 

144 

4 

11 

•927 

151 

8 

4 

•884 

144 

7 

17 

•928 

151 

11 

11 

•885 

144 

11 

0 

•929 

151 

14 

17 

•886 

144 

14 

6 

•930 

151 

18 

0 

•887 

144 

17 

12 

•931 

152 

1 

6 

•888 

145 

0 

19 

•932 

152 

4 

12 

•889 

145 

4 

1 

•933 

152 

7 

19 

•890 

145 

7 

8 

•934 

152 

11 

1 

•891 

145 

10 

14 

•935 

152 

14 

8 

•892 

145 

13 

20 

•936 

152 

17 

14 

•893 

145 

17 

3 

•937 

153 

0 

20 

•894 

146 

0 

9 

•938 

153 

4 

3 

•895 

146 

3 

16 

•939 

153 

7 

9 

•896 

146 

6 

22 

•940 

153 

10 

16 

ASSAY   TADLE. 


xlv 


If  200  Grains  of 

One  Ton  of  Ore 

If  200  Grains  of    One  Ton  of  Ore 

Ore  give  of 

will  yield  of 

Ore  give  of 

will 

yield  of 

FINE   METAL 

FIXE   METAL 

FINE   METAL 

FINE  METAL 

Gr. 

Oz. 

Dwts. 

Grs. 

Gr. 

Oz. 

Dwts. 

Grs. 

•941 

153 

13 

22 

•985 

160 

17 

6 

•942 

153 

17 

4 

•986 

161 

0 

22 

•943 

154 

0 

11 

•987 

161 

4 

4 

•944 

154 

3 

17 

•988 

161 

7 

11 

•945 

154 

7 

0 

•989 

161 

10 

17 

•946 

154 

10 

6 

•990 

161 

14 

0 

•947 

154 

13 

12 

•9!U 

161 

17 

6 

•948 

154 

16 

19 

•992 

162 

0 

12 

•949 

155 

0 

1 

•993 

162 

3 

19 

•950 

155 

3 

8 

•994 

162 

7 

1 

•951 

155 

6 

14 

•995 

162 

10 

8 

•952 

155 

9 

20 

•996 

162 

13 

14 

•953 

155 

13 

3 

•997 

162 

16 

20 

•954 

155 

16 

9 

•998 

163 

0 

3 

•955 

155 

19 

16 

•999 

163 

3 

9 

•956 

156 

2 

22 

1 

grain 

163 

6 

16 

•957 

156 

6 

4 

2 

326 

13 

8 

•958 

156 

9 

11 

3 

490 

0 

0 

•959 

156 

12 

17 

4 

653 

6 

16 

•960 

156 

16 

0 

5 

816 

13 

8 

•961 

156 

19 

6 

6 

980 

0 

0 

•962 

157 

2 

12 

7 

1143 

6 

16 

•963 

157 

5 

19 

8 

1306 

13 

8 

•964 

157 

.  9 

1 

9 

1470 

0 

0 

•965 

157 

12 

8 

10 

1633 

6 

16 

•966 

157 

15 

14 

11 

1796 

13 

8 

•967 

157 

18 

20 

12 

1960 

0 

0 

•968 

158 

2 

3 

13 

2123 

6 

16 

•969 

158 

5 

9 

14 

22$6 

13 

8 

•970 

158 

8 

16 

15 

2450 

0 

0 

•971 

158 

11 

22 

16 

2613 

6 

16 

•972 

158 

15 

4 

17 

2776 

13 

8 

•973 

158 

18 

11 

18 

2940 

•  o 

0 

•974 

159 

1 

17 

19 

3103 

6 

16 

•975 

159 

5 

0 

20 

3266 

13 

8 

•976 

155* 

8 

6 

21 

3430 

0 

0 

•977 

159 

11 

12 

22 

3593 

6 

16 

•978 

159 

14 

19 

23 

3756 

13 

8 

•979 

159 

18 

1 

24 

3920 

0 

0 

•980 

160 

1 

8 

25 

4083 

6 

16 

•981 

160 

4 

14 

26 

4246 

13 

8 

•982 

160 

7 

20 

27 

4410 

0 

0 

•983 

160 

10 

3 

28 

4573 

6 

16 

•984 

160 

14 

9 

29 

4736 

13 

8 

xlvi 


ASSAY   TABLE. 


i 

If  200  Grains  of  One  Ton  of  Ore 

If  200  Grains 

of  One 

Ton  of  Ore 

Ore  give 

of     will 

yield 

of 

Ore  give  of 

will  yield  of 

FINE  METAL      FINE  METAL 

FINE  METAL 

FINE  METAL 

Grs. 

Oz. 

Dwts. 

Grs. 

Grs. 

Oz. 

Dwts. 

Grs. 

30 

4900 

0 

0 

74 

12086 

13 

8 

31 

5063 

6 

16 

75 

12250 

0 

0 

32 

5226 

1.3 

8 

76 

12413 

6 

16 

33 

5390 

0 

0 

77 

12576 

13 

8 

34 

5553 

6 

16 

78 

12740 

0 

0 

35 

5716 

13 

8 

79 

12903 

6 

16 

36 

5880 

0 

0 

80 

13066 

13 

8 

37 

6043 

6 

16 

81 

13230 

0 

0 

38 

6206 

13 

8 

82 

13393 

6 

16 

39 

6370 

0 

0 

83 

13556 

13 

8 

40 

6533 

6 

16 

84 

13720 

0 

0 

41 

6696 

13 

8 

85 

13883 

6 

16 

42 

6860 

0 

0 

86 

14046 

13 

8 

43 

7023 

6 

16 

87 

14210 

0 

0 

44 

7186 

13 

•  8 

88 

14373 

6 

16 

45 

7350 

0 

0 

89 

14536 

13 

8 

46 

7513 

6 

16 

90 

14700 

0 

0 

47 

7676 

13 

8 

91 

14863 

6 

16 

48 

7840 

0 

0 

92 

15026 

13 

8 

49 

8003 

6 

16 

93 

15190 

0 

0 

50 

8166 

13 

8 

94 

15353 

6 

16 

51 

8330 

0 

0 

95 

15516 

13 

8 

52 

8493 

6 

16 

96 

15G80 

0 

0 

53 

8656 

13 

8 

97 

15843 

6 

16 

54 

8820 

0 

0 

98 

16006 

13 

8 

55 

8983 

6 

16 

99 

16170 

0 

0 

56 

9146 

13 

8 

100 

16333 

6 

16 

57 

9310 

0 

0 

101 

16496 

13 

8 

58 

9473 

6 

16 

102 

16660 

0 

0 

59 

9636 

13 

-8 

103 

16823 

6 

16 

60 

9800 

0 

0 

104 

16986 

13 

8 

61 

9963 

6 

16 

105 

17150 

0 

0 

62 

10126 

13 

8 

106 

17313 

6 

16 

63 

10290 

0 

0 

107 

17476 

13 

8 

64 

10453 

6 

16 

108 

17640 

0 

0 

65 

10616 

13 

8 

109 

17803 

6 

16 

66 

10780 

0 

0 

110 

17966 

13 

8 

67 

10943 

6 

16 

111 

18130 

0 

0 

68 

11106 

13 

8 

112 

18293 

6 

16 

69 

11270 

0 

0 

113 

18456 

13 

8 

70 

11433 

6 

16 

114 

18620 

0 

0 

71 

11596 

13 

8 

115 

18783 

6 

16 

72 

11760 

0 

0 

116 

18946 

13 

8 

73 

11923 

6 

16 

117 

19110 

0 

0   I 

ASSAY    TABLE. 


xlvii 


If  200  Grains 

of  One  Ton  of  Ore     |  If  200  Grains  of  One 

Ton  of  Ore 

Ore  give  of 

will  yield  of 

Ore  give  of 

will  yield 

of 

FIXE  METAL 

FIXE  METAL 

FIXE  METAL 

FINE  METAL 

G'rs. 

Oz. 

Dwts.  Grs. 

Grs. 

02. 

Dwts 

.  Grs. 

118 

19273 

6 

16 

160 

26133 

6 

16 

119 

19436 

13 

8 

•  161 

26296 

13 

8 

120 

19600 

0 

0 

162 

26460 

0 

0 

-  121 

19763 

6 

16 

163 

26623 

6 

16 

122 

19926 

13 

8 

164 

26786 

13 

8 

123 

20090 

0 

0 

165 

26950 

0 

0 

124 

20253 

6 

16 

166 

27113 

6 

16 

125 

20416 

13 

8 

167 

27276 

13 

8 

126 

20580 

0 

0 

168 

27440 

0 

0 

127 

20743 

6 

16 

169 

27603 

6 

16 

128 

20906 

13 

8 

170 

27766 

13 

8 

129 

21070 

0 

0 

171 

27930 

0 

0 

130 

21233 

6 

16 

172 

28093 

6 

16 

131 

21396 

13 

8 

173 

28256 

13 

8 

132 

21560 

0 

0 

174 

28420 

0 

0 

133 

21723 

6 

16 

175 

28583 

6 

16 

134 

21886 

13 

8 

176 

28746 

13 

8 

135 

22050 

0 

0 

177 

28910 

0 

0 

136 

22213 

6 

16 

178 

29073 

6 

16 

137 

22376 

13 

8 

179 

29236 

13 

8 

138 

22540 

0 

0 

180 

29400 

0 

0 

139 

22703 

6 

16 

181 

295H3 

6 

16 

140 

22866 

13 

8 

182 

29726 

13 

8 

141 

23030 

0 

0 

183 

29890 

0 

0 

142 

23193 

6 

16 

184 

30053 

r> 

16 

143 

23356 

13 

8 

185 

30216 

13 

8 

144 

23520 

0 

0 

186 

30380 

0 

0 

145 

23683 

6 

16 

187 

30543 

6 

16 

146 

23846 

13 

8 

188 

30706 

13 

8 

147 

24010 

0 

0 

189 

30870 

0 

0 

148 

24173 

6 

16 

190 

31033 

(> 

16 

149 

24336 

13 

8 

191 

31196 

13 

8 

150 

24500 

0 

0 

192 

31360 

0 

0 

151 

24663 

fi 

16 

193 

31523 

6 

16 

152 

24826 

13 

8 

194 

31686 

13 

8 

153 

24990 

0 

0 

195 

31850 

0 

0 

154 

25153 

6 

16 

196 

32013 

6 

16 

155 

25316 

13 

8 

197 

32176 

13 

8 

156 

25480 

0 

0 

198 

32340 

0 

0 

157 

25643 

6 

16 

199 

32503 

6 

16 

158 

25806 

13 

8 

200 

32666 

13 

8 

159 

25970 

0 

0 

INDEX 


ACI 

ACID,  NITEIC,  213 
—  oxalic,  168 

—  tartaric,  168 

—  vitrified  boracic,  221 
Agate,  244 

Agents,  oxidising.  170 

—  reducing,  i63 

—  sulphurising,  188 

Alabaster,  gypsum  or  selenite,  256,  285 
Alkalies  and  alkaline  carbonates.  445 

—  and  their  carbonates,  caustic,  187 

—  the  caustic,  180 

Alkaline  carbonates  and  alkalies,  445 

—  persulphides,  189 

Alloy,  tables  for  ascertaining  the  standard 

of  silver,  582 
Alloys,  assay  of,  690 

—  of  gold,  assay,  682 
--of  lead,  470 

—  of  silver  and  copper,  assay  of,  565. 
569,  665 

—  of  zinc,  515 
Almandine,  797 

Almond  or  linseed  meal,  108 
Alumina  crucibles,  123 
Alumina,  lime,  and  magnesia,  192 
Amalgamation.  564 
Amethyst,  244,  803 
Ammonium  oxalate.  168 
Analysis  by  the  wet  way,  comparison  of 
the  results,  399 

—  of  platinum  ores  from  various  sources. 
719 

—  volumetric,  293 
Anglesite,  266,  285 
Anthracite,  165 

Antimonial  and  arsenical  silver  ores.  272. 

277.  279 
Antimony,  172 

—  assay  of,  497 

—  regains  of,  499 

—  and  lead  sulphides,  272,  277,  278 

—  sulphide,  189,  258,  278 
Antique  emerald,  807 
Anvil,  the,  11 

Apatite,  253,  284,  286 

Apparatus,  auxiliary  blowpipe,  210 

—  furnace,  65 
Aqua-marine,  805 


ASS 

Aragonite,  255,  284 

Argol,  198 

Arsenic,  171,  259,  279 

—  assay  of,  749 

—  sulphide,  252,  282 

Arsenical  and  antimonial  silver  ores,  272, 

277,  279 

-  nickel,  263,  279 
Ash,  bone,  222 

—  in  fuel,  amount  of,  255 
Ashpit,  56 

Assay,  English  copper,  381 

—  from  the  ingot,  625 

—  of  alloys,  690 

—  antimony,  497 

—  arsenic,  749 

-  bismuth,  728 

—  volumetric,  736 

—  chromium,  739 

—  cobalt  and  nickel,  757 

—  copper,  380 

-  pyrites,  424 

—  galena,  460 

—  gold,  666 

—  alloys,  682 

—  coin  and  bullion,  689 

-  iron,  303 

—  in  the  dry  way,  304 

—  wet  way,  317 

—  ores,  complete,  326 

—  lead,  444 

—  manganese,  751 

—  mercury,  527 

—  in  the  dry  way,  529 
nickel  and  cobalt,  757 

—  speiss,  772 

—  platinum  ores,  700 

—  pyrites  for  gold,  694 

—  ores  of  zinc  of  the  first  class,  509 
pure  or  nearly  pure  silver,  612 

—  regulus  of  antimony,  499 

—  saltpetres,  177 
silver,  538 

—  bullion  in  the  wet  way,  573 

—  sulphur,  775 
tin,  478 

—  zinc,  508 

—  zinc   ores   of   the   second   class, 
513 


INDEX. 


ASS 

Assay,  proper,  of  silver  bullion,  569 

—  roasting  and  reducing,  457 

—  size  of,  228 

—  weights  for  silver  and  gold,  32 

—  with  sulphuric  acid,  459,  470 
Assaying  silver  bars,  625 
Assays  in  the  wet  way,  402 

—  parting,  692 

—  volumetric  copper,  417 
Atmosphere,  oxygen  of,  181 
Atomic  weights,  6 
Augite  and  hornblende,  246 


T>ALANCE,  the,  23 
_D    Bars  of  furnace,  57 
Barytes  or  heavy  spar,  257,  285 
Beale's  cement,  113 
Beryl,  blue,  802 

—  or  emerald,  249,  288 

Binary  compounds  containing  no  oxygen,  5 
Bismuth,  173,  258,  281 

—  ores,  assay  of,  728 
containing  copper,  729 

—  purification  of,  733 
Bisulphate  of  potassium,  226 

—  of  sodium,  221 
Black  flux,  197 
Blacklead  crucibles,  116 

—  or  graphite,  164,  253,  281 

Blast   and  wind    furnaces,    effects   pro- 
duced by,  70 

—  furnaces,  58 
Blende,  264,  281,  284 
Blowpipe,  203 

—  apparatus,  auxiliary,  210 

—  assay  of  coal  before  the,  158 

mercury,  537 

silver,  641 

—  detection  of  copper,  441 
nickel,  766 

—  determination  of  minerals,  274 

—  Faraday's  directions  for  using,  206 

—  flame,  208 

—  jets,  205 

—  operations,  general  routine  of,  228 

—  reagents  and  fluxes,  213 
Blue  stones,  801 

Boiler  cement,  113 
Bone  ash,  222 
Boracic  acid,  vitrified,  221 
Borate  of  lead,  201 
Borates  and  lead  silicates,  176 
Borax,  192,  218 
Brazil-wood  paper,  213 
Bricks,  magnesia  crucibles  and,  123 
Brown  and  flame-coloured  stones,  797 
Brown  ferric  oxide,  261 
Brown's    method    by    sodium    hyposul- 
phite, 421 

Bruyere's  cement,  113 
Buisson's  volumetric  process,  475 
Bullion  and  gold  coin  assay,  689 


CIN 

Bunsen's  gas  burner,  100 

Burettes,  297 

Burner,  solid  flame,  106 


nAIRNGOKM,  244 

\J     Gale-spar  or  calcite,  254,  281,  284 

Calcination,  40 

Calcining  furnace,  53 

Calcite  or  calc-spar,  254,  281,  284 

Calorific  power  of  fuel,  150 

Calorimeter,  lire's,  150 

—  Wright's,  151 
Caoutchouc,  110    ' 
Carbon,  164 

Carbon,  estimation  of,  337 

combined,  341 

Carbonate,  iron,  263,  284 

—  of  potash,  fusion  with,  447 
soda,  214 

Carbonates,  alkaline  and  alkalies,  445 

—  potassium  and  sodium,  180,  194 

—  caustic  alkalies,  187 

Carbonic  acid,  determination  of,  332 
Carbonisation,  volatile  product  of,  153 
Carnelian,  245 
Cement,  Beale's,  113 

—  boiler,  113 

—  Bruyere's,  113 

—  iron,  112 

—  oxychloride  of  zinc,  113 

—  resinous  or  hard,  110 

—  Koman,  108 

—  soft,  109 

—  waterproof,  109 
Cements  and  lutes,  107 
Ceruse  and  litharge,  200 

—  or  white  lead,  171 
Cerusite.  266,  284 
Chalcedony,  244 
Charcoal,  67,  181 

—  crucibles,  119 

—  or  coke,  examination  of,  155 

—  wood,  165 
Chatoyant,  806 

Chemical  characters  of  minerals,  239 

—  furnace,  double-jacketed,  82 

—  nomenclature,  1 

—  symbols,  7 

Chimney  of  calcining  furnace,  54 

—  of  wind  furnace,  57 
Chisel,  the  cold,  13 
Chloride,  dry  silver,  223 

—  process,  626 
Chlorite,  246 

Chrome  iron  ore,  assay  of,  739 
Chromic  iron,  262 
Chromium,  assay  of,  739 

—  in  iron  and  steel,  745 
Chrysoberyl,  252,  289,  792 
Chrysolite  or  olivine,  247 
Chrysoprase,  805 
Cinnabar,  189,  267,  277,  282 


INDEX. 


li 


cm 

Cinnamon  stones,  799 
Classification  of  minerals  containing  lead, 
444 

-  of  ores  containing  zinc.  508 
Coal,  67,  253 

—  before  the  blowpipe,  assay  of,  158 

—  elementary  analysis  of,  143 

—  illuminating  gas  from,  161 

Cobalt  and  nickel,  complex  ores  of,  767 
separation  of,  763 

—  bloom,  264 

—  nitrate,  221 

—  ores,  757 
Coke,  67,  165 

—  or  charcoal,  examination  of,  155 
Colorimetric  assays,  405 

—  copper  assay,  402 

—  method,  Heines's,  403 
Colour  and  streak  of  minerals,  234 
Colours,    stones    possessing    a   play   of. 

806 

Combination,  laws  of,  5 
Combustion,  42 
Copper,  174,  213 

—  and  iron  pyrites,  assay  of,  775 

—  assay,  380 

English,  381 

volumetric,  417 

—  assays,  classification  of,  381 
—  colorimetric,  402 

—  bismuth  ores  containing   729 

-  blowpipe  detection  of,  44 1 

—  carbonates,  270,  282 

-  coarse,  386.  396 

—  from  zinc,  separation  of,  525 

—  grey,  269,  278 

—  iron  and  lead  sulphates,  181 

—  native,  268,  280 

—  oxide,  180,  201,  221 

— •  oxides  upon  lead,  action  of,  175 

-  pyrites,  268,  277 
assay  of,  424 

—  silver,  lead,  or  mercury  selenidr,  272 

—  sulphide  of,  385 
vitreous,  268,  278 
zinc,  nickel  alloys,  769 

Cornish  crucibles,  114 
Corundum  or  sapphire,  250,  289 
Cream  of  tartar,  198 
Crucibles,  113 

—  alumina,  123 

—  and  bricks,  magnesia,  123 

-  black-lead,  116 

—  charcoal,  119 

—  earthen,  116 

—  good  and  bad,  117 

—  lime,  121 

—  lined,  120 

—  malleable  iron,  126 

—  mounts  for,  103 

—  of    the    Patent    Plumbago    Crucil  le 
Company,  115 

—  platinum,  126 


FLU 

Crucibles,  porcelain,  115 

—  silver,  133 

—  Stourbridge,  115 
Crysolite,  804 

Crystalline  form  of  minerals,  232 
Cupellation,  42,  52,  558,  565,  675 
Cupel  or  muffle  furnace,  60 
Cupels,  133 

manufacture  of,  1 34 
Cupric  oxide,  black,  269 
Cupriferous  products,  special,  399 
Cuprous  oxide,  red,  269,  281 
Cyanide  of  potassium,  214 
Cyanite,  801 
Cymophane,  792,  807 


DANIEL'S  pyrometer,  137 
Debray's  and    Deville's  process  for 
platinum  ores,  714 
Desulphurising  agents,  181 
Diamond,  252,  289,  783 
Dichroite,  802 
Disthene,  801 
Distillation,  49 

Docimastic  determination  of  lead.  470 
Dolomite,  255,  284 
Dressing,  washing,  and  vanning,  1 9 


EAETHEN  crucibles,  116 
Egg  and  lime  lute,  108 
Electric  pyrometer,  140 
Elements,  list  of,  2 

—  metallic,  3 
Elutriation,  19 
Emerald,  805 

-  antique,  807 

—  or  beryl,  249,  288 

—  yellow,  794 
Essonite,  799 


FALSE  topaz,  244 
Faraday's   directions  for  using  the 
blowpipe.  206 
Fat  lute,  108 
Fatty  oils,  166 
Felspar,  249,  286,  208 

-  nacreous,  808 

Ferric  oxide,  red  and  brown,  261 
Ferrous  oxide,  estimation  of,  33 
Fire  lute,  107 
Fish-eye,  808 
Flames,  coloured,  290 
Fletcher's  injector  gas  furnace,  87 

—  universal  gas  furnace,  82 
Flint  or  hornstone,  245 

Flores  Dumonte's  method  of  lead   assay. 

472 

Fluorspar,  194,  222,  254,  286 
Flux  black,  197 

—  fusion  with  black,  452 


lii 


INDEX. 


FLU 

Flux,  raw,  196 

—  Turner's,  222 

—  white,  197 
Fluxes,  190 

—  reducing  power  of  various,  199 
Forbes's  D  blowpipe,  203 

-  blowpipe  assay,  641 
Forceps,  platinum  glass,  48 
Fracture  in  minerals,  mode  of,  233 
Fuel,  amount  of  ash  in,  155 

—  amount  of  sulphur  in,  156 

—  assay  and  analysis  of,  142 

—  calorific  power  of,  150 

—  composition  of,  142 

—  determination  of  the  absolute  heating 
power,  146 

—  determination  of  the  adhering  water 
in,  144 

—  external  appearance  of,  1 44 

—  for  furnace,  68 

—  peculiarities  of,  158 

—  pyrometric  examination  of,  153 

—  specific  gravity  of,  145 

—  specific  heating  power  of,  153 
Furnace  apparatus,  65 

—  bars,  57 
-  blast,  58 

—  calcinating,  53 

—  double-jacketed  chemical,  82 

—  gas,  78^  82,  89 

—  Griffin's  gas,  78 
—  oil  lamp,  72 

—  fuel  for,  68 

—  fusion,  55 

—  management  of  oil  lamp,  74 

—  muffle  or  cupel,  60 

—  operations,  64 

—  power  of  the  oil-lamp,  77 

—  reverberatory  gas,  95 

—  tongs,  65 

—  universal,  63 

-  wind,  55 
Furnaces,  53 

—  effects  produced  by  wind  and  blast,  70 

—  evaporating,  55 

—  methods  of  measuring    the    heat   of, 
136 

—  oil  and  gas,  72 
Fusibility  of  minerals,  238 
Fusion,  46 

—  furnace,  55 


/1ALEXA,  189,  265,  278 
VJ   _  assay  of,  460 

—  method  of  separating  silver  from,  565 
Garnet,  248,  285,  289,  807 

—  deep  red,  799 

—  noble,  797,  799 

—  vermiel,  797 

Gas  and  oil  furnaces,  72 

—  burner,  Eunsen's,  100 

—  from  coal,  illuminating,  161 


HES 

Gas  furnace,  injector,  87 

—  furnace,  87,  82,  89 

reverberatory,  95 

universal,  82 

temporary,  105 

—  hydrogen,  163 

—  principles  of  heating  by,  99 
Gay-Lussac's  mode  of  assaying  saltpetre, 

177 

—  process,  application  of.  585 
Gems,  217 

—  and   precious   stones,  discrimination 
of,  783 

—  glass  and  artificial,  809 

Gibbs,  W.,  process  for  chrome  iron  ore, 
742 

—  process  for  platinum,  723 
Glass,  192,  193 

—  and  artificial  gems,  809 

—  and  platinum  forceps,  48 

—  of  lead,  200 
Gold,  271,  280 

—  alloys,  assay  of,  682 
standard,  689 

—  assay,  666 

—  assay  of  pyrites  for.  694 

—  and  silver  assay  weights,  32 

—  coin  and  bullion  assay,  689 

—  in  minerals,  detection  of,  696 

—  native,  667 

—  ores,  assay  of,  667 

—  valuing  table  (Appendix),  ii 
Gore's  gas  furnace,  89 
Graphite,  estimation  of,  338 

—  or  blacklead,  164,  253,  281 

-  value  of,  164 

Gravity,  specific,  of  fuel,  145 

—  specific,  of  minerals,  236 
Greenearth,  262,  282 

-  stones,  804 

Grey  copper,  269,  278 
Griffin's  gas  furnace,  78 

—  oil-lamp  furnace,  72 

-  reverberatory  gas  furnace,  95 
Gum,  168 

Guyard's  process  for  platinum  ores,  718 
Gypsum,  222 

-  selenite,  or  alabaster,  256,  285 


HAEMATITE,  specular  iron  or  mica- 
ceous iron,  261,  280 
Hammers,  12 
Hardness  of  minerals,  234 
Heating  by  gas,  principles  of,  99 
Heating  power  of  fuel,  determination  of 

absolute,  146 
Heat  of  furnaces,  methods  of  measuring, 

136 

-  production  and  application  of,  53,  67 
Heavy  spar  or  barytes,  257,  285 
Heine's  colorimetric  method.  403 
Hessian  pots,  114 


INDEX. 


'liii 


HOO 

Hood,  tlie,  55 

Horn  silver,  272,  285 

Hornblende  and  augite,  246 

Hyacinth,  797 

—  or  zircon,  249,  288,  289 

Hydrogen  gas,  163 


TNCINEKATION,  42 

J_     Ingot,  assay  from  the,  625 

moulds,  67 
Inquartation,  680 
Iron,  173 

—  and  copper  pyrites,  assay  of,  775 

—  and  steel,  chromium  in,  745 
assay,  303 

—  carbonate,  263,  284 

—  cement,  112 
-   chromic,  262 

crucibles,  malleable,  126 

—  estimation  of,  370 
fusion  with  metallic,  453 

—  in  the  dry  way,  assay  of,  303 

-  wet  way,  assay  of,  317 
lead,  and  copper  sulphates,  181 

—  magnetic,  260,  280 
metallic,  169,  181 
native,  259,  280 

—  ore,  assay  of  chrome,  739 
ores,  a  list  of  principal,  303 

--  oxides,  201 
peroxide,  180 
pyrites,  189,  260,  277 
—  magnetic,  274 

—  titanic,  262,  280 

—  wire,  213 


TACQUELAIN'S    and    Von    Hubert's 
fj      colorimetric  assays,  413 
Jasper,  245 


LADLE,  67 
Lead,  action  of  copper  oxide  on,  175 

—  alloys  of,  470 

—  and  antimony   sulphides,    272,    279, 
278 

—  assay  of,  444 

—  borate,  201 

—  copper,  and  iron  sulphates,  181 

—  silver,  or  mercury  selenide,  272 

—  glass  of,  200 

-  -  metallic,  170 

—  nitrate,  180,  188 

—  on  the  metals,  action  of  oxide  of.  171 

-  proof,  223 

—  silicates  and  borates,  176  . 

—  sulphate,  188 

—  white,  mixed  with  oil,  108 

—  or  ceruse,  171 

Lea's  process  for  analysing  platinum  ores, 
709 


MIN 

Level's  fusion  assay,  472 
Lime  and  egg  lute,  108 

—  crucibles,  121 

—  magnesia,  alumina,  and  their  silicates, 
192 

Linseed  or  almond  meal,  108 
Litharge,  170,  182 

—  action  of,  on  sulphide,  182 

—  and  ceruse,  200 
Litmus  paper,  blue,  213 

—  red,  213 
London  pots,  113 
Luckow's  process  for  the  estimation  of 

copper,  434 

Lustre  of  minerals,  233 
Lute,  fat,  108 

—  fire,  107 

—  lime  and  egg,  108 
Lutes  and  cements,  107 


1 TAGXESIA  crucibles  and  bricks,  123 
ILL      -  lime,   and  alumina,   and  their 

silicates,  192 
Magnesite,  255,  284 
Magnetic  iron,  260.  280 

-  pyrites,  274 
Makin's  method,  686 
Manganese,  assay  of,  751 

—  estimation  of,  366 
-   ores,  263,  280 

—  valuation  of,  751 

—  peroxide,  180 

Meal,  linseed  or  almond,  108 
Mercury,  blowpipe  assay  of,  537 

—  lead,  silver,  or  copper  selenide,  272 

—  or  quicksilver,  267 

—  volumetric  estimation  of,  533 
Metallic  elements,  3 

—  fluxes,  a  list  of,  191,  20Q 

—  iron,  169, 181 

—  fusion  with,  453 

—  lead,  170 

—  lustre,  minerals  possessing  a,  275 

—  oxides,  reduction  of,  216 
M.-ta Holds,  2 

Metals,  action  of  oxide  of  lead  on  the, 
171 

—  influence  of  foreign,  397 

—  separating  silver  from  the  baser,  571 
Mica,  250r  285 

Microcosmic  salt,  219 

Millerite,  273 

Minerals,  chemical  characters  of,  239 

—  colour  and  streak  of  234 
crystallime  form  of,  232 

—  determination  of,  274 

—  discrimination  of,  231 

—  fusibility  of,  238 
hardness  of,  234 
lustre  of,  233 

—  mode  of  fracture,  233 

—  possessing  a  metallic  lustrej  275 


liv 


INDEX. 


MIX 

Minerals,  specific  gravity.  236 

Mispickel,  260,  27? 

Mohr's   method  for    the   estimation    of 

zinc,  523 

Molybdenite,  258,  277,  281 
Mortar  and  pestle,  13 
Muffle  or  cupel  furnace,  60 
Muir's  assay  of  bismuth,  737 


VTICKEL  and  cobalt  ores,  complex,  767 
ll     —  and  cobalt,  separation  of,  763. 

—  arsenical,  263,  279 

—  before  the  blowpipe,  detection  of,  765 

—  ores,  757 

—  oxalate,  221 

—  speiss,  assay  of,  772 
-  sulphide,  273,  278 

—  zinc,  and  copper  alloys,  769 
Nitrate,  cobalt,  221 

—  lead,  180,  188 

—  potassium,  188,  195 

Nitrates,  potassium  and  sodium,  176 
Nitre,  188,  220,  256 
Nitric  acid,  213 
Nomenclattire,  chemical,  1 
Non-metallic  elements,  2 

—  fluxes,  a  list  of,  191 


OIL  and  gas  furnaces,  72 
Oil- lamp  furnace,  management   of, 
74 

power  of,  77 

-  -  white  lead  mixed  with,  108 

Oils,  fatty,  166 

Olivine  or  chrysolite,  247 

Onyx  or  sardonyx,  245 

Opal,  245 

Ores,  manganese,  263,  280 

—  of  cobalt,  757 

nickel,  757 

Osm-iridium,  analysis  of,  722 
Oxalate,  ammonium,  168 

—  nickel,  221 
Oxalic  acid,  168 
Oxidations,  208,  209 

Oxide  of  copper,    180,  201,    221,    269, 
281 

lead  on  the  metal",  action  of,  171 

-  tin,  478 

—  red  and  brown  ferric,  261 
Oxides,  4 

—  action  of  copper  on  lead.  175 

—  of  iron,  201 

—  reduction  of  metallic,  217 
Oxidising  agents,  170 

—  reagents,  fusion  with,  541 
Oxychloride  of  zinc  cement,  113 
Oxygen,  170 

T  binary  compounds  containing  no,  5 

—  of  the  atmosphere,  181 


RED 

T)APER,  blue  litmus,  213 
JL       —  Brazil-wood,  213 
-  red  litmus,  213 

—  turmeric,  213 
Paris,  plaster  of,  108 
Pearson's  assay  of  bismuth,  736 
Penny's   process  for  the    assay  of  iron, 

319 

Perchloride  of  tin  process,  322 
Peridot,  804 
Peroxide  of  iron,  180 

—  of  manganese,  180 

Perry,  R.  W.,  assay  of  platinum  ores, 

723 

Persulphides,  alkaline,  189 
Pestle  and  mortar,  13 
Phosphorus,  estimation  of,  364 
Pipette,  301 
Pitchblende,  274 
Plaster  of  Paris,  108 
Platinum,  270,  280 

—  and  glass  forceps,  48 

—  crucibles,  126 
—  cleaning,  131 

preservation  of,  130 

—  ores,  assay  of,  700 
Plumbago  crucibles,  115 
Plumbiferous  minerals,  399 
Poker  or  stirring  rod,  66 
Porcelain  crucibles,  115 

Potassium  and  sodium  carbonates,  180, 
194 

—  nitrates,  176 

—  bisulphate,  220 

—  carbonate,  fusion  with,  446 

—  cyanide,  214 

-  nitrate,  188,  195 
Pots,  London,  113 
Pyrites,  384 

—  assay  of  copper,  424 

—  and  iron,  775 

—  for  gold,  assay  of,  694 

-  iron,  189,  260,  277 

-  magnetic  iron,  274 

—  sulphur  in,  777 
Pyrometer,  electric,  140 
Pyrometers,  136 

Pyrometric  examination  of  fuel,  153 
Pyromorphite,  266,  285 


QUARTZ,  244,  288,  787,  807 
—  and  silicates,  243 

—  violet,  803 

—  yellow,  797 

Quicksilver  or  native  mercury,  267 


RAW  flux,  196 
Red  and  rose-coloured  stones,  799 
—  ferric  oxide,  261 
Reducing  agents,  163 


INDEX. 


Iv 


RED 

Reducing  and  roasting  assay,  457 
—  power  of  agents,  169 

—  of  various  fluxes,  199 
Reduction,  44,  208,  209 
Regulus,  fusion  for,  392 
Resinous  or  hard  cement,  110 
Resins,  166 

Results,  calculation  of,  158 
Retorts,  52 
Roasting,  42 
Rock  crystal,  244 
-  salt,  256 

Rod,  poker  or  stirring,  66 
Roman  cement,  108 
Rose  quartz,  244 
Ruby,  oriental,  799 
—  spinel,  799 
Rutile,  273 


OALT,  common,  195 

O     —  measurement  of  the  solution  of, 

575 
Salt,  microcosmic,  219 

—  of  sorrel,  199 
Saltpetre,  188 
Saltpetres,  assay  of,  177 
Salts,  4 

Sample,  preparation  of,  9 
Sapphire  or  corundum,  807,  250,  289 
-  blue,  801 

—  green,  804 

—  red,  799 

—  violet,  803 

—  yellow,  792 

—  water,  802 

—  white,  789 

Schwartz's  method  for  lead  assay,  473 

the  estimation  of  zinc,  522 

Scorification.  42,  52,  549 

Scorifiers,  136 

Selenide,  mercury,  lead,  silver,  or  copper, 

272 

Selenite,  alabaster  or  gypsum,  256,  285 
Selenium,  171 
Serpentine,  246 
Shears,  small,  13 
Siemens's  electric  pyrometer,  140 
Sieve,  the,  16 
Silica,  192,  222 

Silicates  and  berates,  lead,  176 
Silicon,  estimation  of,  356 
Silver,  271,  280 

—  alloy,  tables  for  ascertaining  the  stan- 
dard of,  592 

—  alloys  containing  mercury,    modifica- 
tions required  in,  624 

and  copper  alloys,  assay  of,  565,  569, 
665 

-  and  gold  assay  weights,  32 

-  assay  of,  538 
blowpipe,  641 


SUL 

Silver  bars,  assaying,  625 

—  bullion,  assay  of  proper,  569 

—  chloride,  dry,  223 

—  crucibles,  133 

—  from  the  baser  metals,  separating,  571 

—  horn,  272,  285 

—  mercury,  lead,  or  copper  selenide,  272 

—  ores,  arsenical  and   antimonial,   272, 
277,  279 

Smaltine,  264,  279 
Soap,  white  or  mottled,  109 
Sodium  and  potassium  carbonates,  180, 
194 

—  nitrates,  176 

—  bisulphate,  221 

—  carbonate,  214 

—  sulphate,  181 
Soft  cement,  109 
Solution,  47 

Solufons,  standard,  297 
Sorrel,  salt  of,  199 
Specific  gravity  of  fuel,  145 
minerals,  236 

-  heating  power  of  fuel,  1 53 

Specular   iron,    haematite    or    micaceous 

iron,  261,  280 
Speiss,  assay  of  nickel,  772 
Sphene,  273 

Spinel,  ruby,  251,  289,  799 
Standard  of  the  alloys  of  gold,  689 

—  solution  of  salt,  table  of  correction  of, 
'     589 

Stanniferous  minerals,  397 
Starch,  167 

Steel  and  iron,  chromium  in,  745 
Steinbeck's  process  for  the  assav  of  cop- 
per, 427 
Stones,  blue,  801 

—  brown  and  flame-coloured,  797 

—  colourless,  783 

—  green,  804 

—  possessing  a  play  of  colours,  806 

—  red  and  rose-coloured,  799 

—  violet,  803 

—  yellow,  792 
Stourbridge  crucibles,  115 
Streak  and  colour  of  minerals,  234 
Sublimation,  52 

Sublimates,  detection  of  antimonv  in,  504 
Sugar,  167 
Sulphate,  lead,  188 

—  sodium,  181 

Sulphates  of  lead,  copper,  and  iron.  181 

—  soluble,  256 

Sulphide,  antimony,  189,  258,  278 

—  nickel,  273,  278 

—  of  copper,  385 

—  of  silver,  271,  278. 

Sulphides,  antimony  and  lead,  272.  277, 

278 
Sulphur,  171,  189,  257,  281 

—  estimation  of,  346 

—  in  fuel,  amount  of,  1 56 


3    K 


Ivi 


INDEX. 


BUL 

Sulphur  in  pyrites,  777 

—  minerals,  775 

Sulphuric  acid,  assay  with,  459,  47<> 

Sulphurising  agents,  188 

Symbols,  chemical,  7 


TABLE,     gold     valuing     (Appendix), 
ii. 

-  of    corrections   of    the    standard   of 
solution  of  salt,  589 

Talc,  245 

Tallow,  166 

Tartaric  acid,  168 

Tellurium,  171 

Temperatures,  comparison  of  high,  141 

Tin,  172 

-  assay  of,  478 
Tinfoil,  223 

Tin  ore,  257,  281 

—  oxide,  478 

—  process,  perchloride  of,  322 
Titanic  iron,  262,  280 
Titanium,  estimation  of,  374 
Tongs,  furnace,  65 

Topaz,  248,  288 
-  blue,  801 

—  reddish,  800 
--  yellow,  793 

—  white,  789 

Touchstone,  examination  of  the,  681 
Tourmaline,  247,  288,  799 

—  blue,  802 

—  green,  805 

—  red,  800 

—  violet,  803 

—  yellow,  793 
Turmeric  paper,  213 
Turner's  flux,  222 
Turquoise,  802 


TJ 


RE'S  calorimeter,  150 


VANNING,  washing,  and  dressing,  19 
Violet  stones,  803 
Volumetric  analysis,  293 

—  assay  of  bismuth,  736 

—  copper  assays,  417 

—  determination  of  zinc,  515 

—  estimation  of  chromium,  747 

mercury,  633 

Von   Hubert's  and   Jacquelain's    color!- 
metric  assays,  413 


ZIB 

WASHING,  dressing,  or  vanning,  19 
Water  sapphire,  802 

—  in  fuel,  determination  of  the  adhering, 
144 

Waterproof  cement,  109 
Wax,  yellow,  108 
Weighing,  method  of,  33 

—  operation  of,  23 

Weight  of  colourless  stones,  comparative 

table,  791 
Weights,  the,  30 

—  for  silver  and  gold  assay,  32 

—  of  blue  stones  comparative  table,  80S 
brown  and  flame-coloured  stones, 

comparative  table,  798 

—  of  green  stones,   comparative   table, 
806 

red  or  rose-coloured  stones,  com- 
parative table,  800 

—  stones  possessing  a  play  of  colours, 
comparative  table,  808 

—  violet  stones,  comparative  table,  804 
—  yellow  stones,  comparative  table, 

796 
White  flux,  197 

—  lead  mixed  with  oil,  108 
and  ceruse,  171 

—  nickel,  273 

—  or  mottled  soap,  199 
Wilson's  pyrometer.  139 

Wind  and  blast  furnaces,  effects  produced 
by,  70 

—  furnace,  55 
Wire,  iron,  213 
Wolfram,  273 
Wood  charcoal,  165 
Wright's  calorimeter,  151 


I 


stones,  792 
Yellow  wax,  108 


ZEOLITES,  250,  285 
Zinc,  173,  213 

—  carbonate,  265 

—  nickel  and  copper  alloys,  769 

—  assay  of,  508 

—  distillation  of  pure,  82 

—  oxychloride  of,  cement,  113 

—  separation  of  copper  from,  525 

—  silicate,  263,  284 

—  volumetric  determination  of,  515 
Zircon,  or  hyacinth,  249,  288,  289,  797 

—  yellow,  792 

—  white,  788 


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